13
N
ervous an
d
C
h
emica
l
Integration
1
. Introductio
n
Animals constantly monitor both their internal and their external environment and make th
e
n
ecessar
y
ad
j
ustments in order to maintain themselves o
p
timall
y
and thus to develo
p
and
r
e
p
ro
d

uce at t
h
e max
i
mum rate. T
h
ea
dj
ustments t
h
e
y
ma
k
ema
yb
e
i
mme
di
ate an
d
o
b
v
i
ous,
f
or exam
pl

e,
fligh
t
f
rom
p
re
d
ators, or
l
on
g
er-term,
f
or exam
pl
e, entr
yi
nto
di
a
p
ause to avo
id
i
mpending adverse conditions. The nature of the response depends, obviously, on the nature
of the stimulus. Only very rarely does a stimulus act directly on the effector system; almost
alwa
y
s a stimulus is received b

y
an a
pp
ro
p
riate sensor
y
structure and taken to the cen-
t
ra
l
nervous s
y
stem, w
hi
c
h
“
d
eterm
i
nes” an a
pp
ro
p
r
i
ate res
p
onse un

d
er t
h
ec
i
rcumstances.
Wh
en a res
p
onse
i
s
i
mme
di
ate, t
h
at
i
s, ac
hi
eve
di
n a matter o
f
secon
d
sor
l
ess,

i
t
i
st
h
e ner-
vous system t
h
at trans
f
ers t
h
e message to t
h
ee
ff
ector system. Suc
h
responses are usua
ll
y
t
emporary in nature. Delayed responses are achieved through the use of chemical message
s
(
viz., hormones) and are
g
enerall
y
lon

g
er-lastin
g
. The nervous and endocrine s
y
stems of
an
i
n
di
v
id
ua
l
are, t
h
en, t
h
es
y
stems t
h
at coor
di
nate t
h
e res
p
onse w
i

t
h
t
h
est
i
mu
l
us. Sem
i
o-
c
h
em
i
ca
l
s, w
hi
c
h
const
i
tute anot
h
er c
h
em
i
ca

l
re
g
u
l
at
i
n
g
s
y
stem, coor
di
nate
b
e
h
av
i
or an
d
d
eve
l
opment among
i
n
di
v
id

ua
l
s. T
h
ey compr
i
se p
h
eromones (
i
ntraspec
i
fic coor
di
nators
)
and allelochemicals (interspecific coordinators), which include kairomones and allomones.
2
. Nervous
S
yste
m
L
ik
et
h
at o
f
ot
h

er an
i
ma
l
s, t
h
e nervous s
y
stem o
fi
nsects cons
i
sts o
f
nerve ce
ll
s (neurons
)
an
d
g
li
a
l
ce
ll
s. Eac
h
neuron compr
i

sesace
ll b
o
d
y (per
ik
aryon) w
h
ere a nuc
l
eus, many
m
itochondria, and other organelles are located, and a cytoplasmic extension, the axon
,
w
hich is usually much branched, the branches being known as neurites. Axons may b
e
lon
g
, as in sensor
y
neurons, motor neurons, and
p
rinci
p
al interneurons, or ver
y
short
,
as

i
n
l
oca
li
nterneurons. O
f
ten,
i
nsect neurons are mono
p
o
l
ar,
l
ac
ki
n
g
t
h
e
d
en
d
r
i
t
i
c tree

c
h
aracter
i
st
i
co
f
verte
b
rate nerve ce
ll
s, t
h
oug
hbi
po
l
ar an
d
mu
l
t
i
po
l
ar neurons
d
o occur
(

Figure 13.1). Motor (efferent) neurons, which carry impulses from the central nervous
system, are monopolar, and their perikarya are located within a ganglion. Sensory (afferent)
n
eurons are usuall
y
bi
p
olar but ma
y
be multi
p
olar, and their cell bodies are ad
j
acent t
o
4
0
5
4
06
C
HAPTER
13
FI
G
URE 13.1.
N
eurons
f
oun

di
nt
h
e
i
n
-
sect nervous system. Arrows indicate direc-
t
i
on o
fi
mpu
l
se con
d
uct
i
on. (A) Monopo
l
ar;
(
B) bi
p
olar; and (C) multi
p
olar. [After R. F
.
C
hapman, 1971

,
The Insects:
S
tructure and
Function.
B
y perm
i
ss
i
on o
f
E
l
sev
i
er
/
Nort
h
-
Holland, Inc., and the author.]
the sense organ. Interneurons (also called internuncial or association neurons) transmi
t
information from sensory to motor neurons or other interneurons; they may be mono- or
bi
p
olar and their cell bodies occur in a
g
an

g
lion. Interneurons ma
y
be interse
g
mental and
b
ranc
h
e
d
,sot
h
at t
h
evar
i
et
y
o
fp
at
h
wa
y
sa
l
on
g
w

hi
c
hi
n
f
ormat
i
on can trave
l
an
d
,t
h
ere
f
ore,
t
h
evar
i
ety o
f
responses are
i
ncrease
d.
N
eurons are not directly connected to eachotherortothe effector organ but are separate
d
by a minute space, the synapse or neuromuscular junction, respectively. Impulses may be

transferred across the s
y
na
p
se either electricall
y
or chemicall
y
(Section 2.3). The norma
l
diameter of axons is
5
µ
mor
µ
µ
l
ess
;h
owever
,
some
i
nterneurons w
i
t
hi
nt
h
e ventra

l
nerv
e
c
or
d
,t
h
e so-ca
ll
e
d
“
gi
ant fi
b
ers,”
h
ave
di
ameters u
p
to
6
0
µ
m. These giant fibers may run
µµ
t
h

e
l
engt
h
o
f
t
h
e nerve cor
d
w
i
t
h
out synaps
i
ng an
d
are un
b
ranc
h
e
d
except at t
h
e
i
r term
i

n
i
.
T
hey are well suited, therefore, for very rapid transmission of information from sense orga
n
to effector or
g
an; that is, the
y
facilitate a ver
y
ra
p
id but stereot
yp
ed res
p
onse to a stimulu
s
an
df
or some
i
nsects are
i
m
p
ortant
i

n esca
p
e react
i
ons (Ho
yl
e, 1974; R
i
tzmann, 1984).
N
eurons are a
gg
re
g
ate
di
nto nerves an
dg
an
gli
a. Nerves
i
nc
l
u
d
eon
ly
t
h

e axona
l
com
-
p
onent o
f
neurons, w
h
ereas gang
li
a
i
nc
l
u
d
e axons, per
ik
arya, an
dd
en
d
r
i
tes. T
h
e typ
i
ca

l
structures of a ganglion and interganglionic connective are shown in Figure 13.2. In a gan
-
g
lion there is a central neuro
p
ile that com
p
rises a mass of efferent, afferent, and associatio
n
axons. Fre
q
uent
ly
v
i
s
ibl
ew
i
t
hi
nt
h
e neuro
pil
e are
g
rou
p

so
f
axons runn
i
n
gp
ara
ll
e
l
,
k
nown
as fi
b
er tracts. T
h
e
p
er
ik
ar
y
ao
f
motor an
d
assoc
i
at

i
on neurons are norma
lly f
oun
di
nc
l
uster
s
a
dj
acent to t
h
e neurop
il
e
.
Surrounding the neurons are glial cells, which are differentiated according to their
p
osition and function. The peripheral glial (perineural) cells, which form the perineurium
,
4
07
NERV
O
U
S
AND
C
HEMI

CA
L
INTE
G
RATI
ON
F
I
G
URE 1
3
.2
.
C
ross-sect
i
ons t
h
rou
gh
(A) a
bd
om
i
na
lg
an
gli
on an
d

(B)
i
nter
g
an
gli
on
i
c connect
i
ve to s
h
o
w
g
eneral structure. [A, after K. D. Roeder, 1963
,
Nerve Cells and Insect Behaviour
.By
p
ermission of Harvar
d
U
niversity Press. B, after J.E. Treherne and Y. Pichon, 1972, The insect blood-brain barrier
,
A
dv. Insect Physiol.
9
:2
5

7–313. B
yp
ermission of Academic Press Ltd., London, and the authors.]
are ver
y
c
l
ose
ly
assoc
i
ate
dby
t
igh
t
j
unct
i
ons,
f
orm
i
n
g
t
h
e
bl
oo

d
-
b
ra
i
n
b
arr
i
er (Car
l
son
e
t al.,
2000; Kretzsc
h
mar an
d
P
fl
ug
f
e
ld
er, 2002). T
hi
s
b
arr
i

er
i
scr
i
t
i
ca
li
n
i
so
l
at
i
ng t
h
e nervous
system from the hemolymph whose composition is both highly variable and inappropriate
for neuronal function (see Chapter 17, Section 4). However, the barrier itself creates tw
o
p
otential
p
roblems, namel
y
, obtainin
g
ade
q
uate su

pp
lies of ox
yg
en and nutrients for th
e
n
eura
l
e
l
ements. T
h
e
f
ormer
i
sso
l
ve
dbyh
av
i
n
g
trac
h
eae runn
i
n
gd

ee
ply i
nto t
h
e
g
an
gli
a
,
th
e
l
atter
by
t
h
ea
bili
t
y
o
f
t
h
e
p
er
i
neura

l
ce
ll
s to trans
f
er mater
i
a
l
s
b
etween t
h
e
h
emo
ly
m
ph
and neurons. In addition, they secrete the neural lamella, a protective sheath that contain
s
collagen fibrils and mucopolysaccharide. The lamella is freely permeable, enabling the
p
erineural cells to accumulate nutrients from the hemol
y
m
p
h. The inner
g
lial cells occur

amon
g
t
h
e
p
er
ik
ar
y
a
i
nto w
hi
c
h
t
h
e
y
exten
d
fin
g
er
lik
e extens
i
ons o
f

t
h
e
i
rc
y
to
pl
asm, t
h
e
t
ro
ph
os
p
on
gi
um (F
ig
ure 13.3A). T
h
e
f
unct
i
on o
f
t
h

ese ce
ll
s
i
s to trans
p
ort nutr
i
ents
f
ro
m
per
i
neura
l
ce
ll
stot
h
e per
ik
arya. Once
i
nt
h
e per
ik
arya, nutr
i

ents are transporte
d
to t
h
e
ir
site of use by cytoplasmic streaming
.
W
ra
pp
ed around each axon or
g
rou
p
s of smaller axons are other
g
lial (Schwann) cell
s
(
F
ig
ure 13.3B), T
h
ese ce
ll
se
ff
ect
i

ve
ly i
so
l
ate axons
f
rom t
h
e
h
emo
ly
m
ph i
nw
hi
c
h
t
h
e
y
are
b
at
h
e
d
, However,
i

n contrast to t
h
es
i
tuat
i
on
i
n verte
b
rates, t
h
e
gli
a
l
ce
ll
s are not com
p
acte
d
t
o
f
orm a mye
li
ns
h
eat

hb
ut rat
h
er are
l
oose
l
y woun
d
aroun
d
t
h
e axons, Furt
h
er,
i
n
i
nsec
t
n
erves there are no distinct nodes of Ranvier (the regions between adjacent glial cells);
h
ence, saltator
y
conduction of im
p
ulses does not occur (Section 2.3)
.

4
0
8
C
HAPTER
13
F
I
G
URE 13.3
.
(
A) Ce
ll b
o
dy
o
f
motor neuron s
h
ow
i
n
g
tro
ph
os
p
on
gi

um; an
d
(B) cross-sect
i
on t
h
rou
gh
axons
and surrounding Schwann cells. [A, after V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed.,
M
et
h
uen an
d
Co. By perm
i
ss
i
on o
f
t
h
e aut
h
or.B,a
f
ter J. E. Tre
h
erne, an

d
Y. P
i
c
h
on, 1972, T
h
e
i
nsect
bl
oo
d
-
b
ra
in
b
arr
i
er
,
Ad
v. Insect P
hy
sio
l
.
9
:2

5
7–313
.
B
yp
erm
i
ss
i
on o
f
Aca
d
em
i
c Press Lt
d
., Lon
d
on, an
d
t
h
e aut
h
ors.]
Structura
lly
,t
h

e nervous s
y
stem ma
yb
e
di
v
id
e
di
nto (1) t
h
e centra
l
nervous s
y
stem
an
di
ts
p
er
iph
era
l
nerves an
d
(2) t
h
ev

i
scera
l
nervous s
y
stem.
2.1. Central Nervous S
y
stem
T
he central nervous system arises during embryonic development as an ectoderma
l
delamination on the ventral side (Chapter 20, Section 7.3). Each embryonic segment in
-
c
ludes initiall
y
a
p
air of
g
an
g
lia, thou
g
h these soon fuse. In addition, var
y
in
g
de

g
rees o
f
4
0
9
NERV
O
U
S
AND
C
HEMI
CA
L
INTE
G
RATI
ON
F
IGURE 1
3
.4. (A) Latera
l
v
i
ew o
f
anter
i

or centra
l
nervous system, stomatogastr
i
c nervous system, an
d
en
-
d
ocr
i
ne
gl
an
d
so
f
at
ypi
ca
l
acr
idid
; (B)
di
a
g
rammat
i
c

d
orsa
l
v
i
ew o
fb
ra
i
nan
d
assoc
i
ate
d
structures to s
h
o
w
p
aths of neurosecretor
y
axons and relationshi
p
of cor
p
ora cardiaca and cor
p
ora allata; (C) dorsal view of cor
p

ora
car
di
aca to s
h
ow
di
st
i
nct storage an
d
g
l
an
d
u
l
ar zones; an
d
(D,E) transverse sect
i
ons t
h
roug
h
corpora car
di
aca
at
l

eve
l
sa–
a

an
db
–
b

, res
p
ectivel
y
. [A, after F. O. Albrecht, 19
5
3, T
h
e Anatom
y
o
f
t
h
e Migrator
y
Locust.
By
p
ermission of The Athlone Press. B–E, after K. C. Hi

g
hnam, and L. Hill, 1977, The Comparative Endocrinolog
y
o
f
t
h
e Invertebrate
s
,2n
d
e
d
. By perm
i
ss
i
on o
f
E
d
war
d
Arno
ld
Pu
bli
s
h
ers Lt

d
.]
anteroposterior fusion occur so that composite ganglia result. Thus, in an adult insect th
e
central nervous system comprises the brain, subesophageal ganglion, and a varied numbe
r
of ventral
g
an
g
lia.
T
h
e
b
ra
i
n(F
ig
ure 13.4A)
i
s
p
ro
b
a
bly d
er
i
ve

df
rom t
h
e
g
an
gli
ao
f
t
h
ree se
g
ments an
d
f
orms t
h
ema
j
or assoc
i
at
i
on center o
f
t
h
e nervous system. It
i

nc
l
u
d
es t
h
e protocere
b
rum,
d
eutocerebrum, and tritocerebrum. The protocerebrum, the largest and most complex region
of the brain, contains both neural and endocrine (neurosecretory) elements. Anteriorly it
forms the
p
roximal
p
art of the ocellar nerves (the onl
y
occasion on which the cell bodies
o
f
sensor
y
neurons are
l
ocate
d
ot
h
er t

h
an a
dj
acent to t
h
e sense or
g
an), an
dl
atera
lly is
f
use
d
w
i
t
h
t
h
eo
p
t
i
c
l
o
b
es. W
i

t
hi
nt
h
e
p
rotocere
b
rum
i
sa
p
a
i
ro
f
cor
p
ora
p
en
d
uncu
l
ata,
t
he mushroom bodies, so-called because of their outline in cross-section. The mushroom
b
odies are important association centers, receiving sensory inputs, especially olfactory and
visual, and rela

y
in
g
the information to other
p
rotocerebral centers (Strausfeld
e
ta
l.
,
1998
;
G
ronen
b
er
g
, 2001). Furt
h
er, t
h
e
ypl
a
y
a centra
l
ro
l
e

i
n
l
earn
i
n
g
an
d
memor
y
(Sect
i
on 2.4),
an
d
t
h
e
i
rs
i
ze can
b
e
b
roa
dly
corre
l

ate
d
w
i
t
h
t
h
e
d
eve
l
o
p
ment o
f
com
pl
ex
b
e
h
av
i
or
p
atterns.
T
h
ey are most

hi
g
hl
y
d
eve
l
ope
di
nt
h
e soc
i
a
l
Hymenoptera. In wor
k
er ants,
f
or examp
l
e
,
t
hey make up about one-fifth the volume of the brain. The median central body is an
other important association center, one function of which appears to be the coordinatio
n
41
0
C

HAPTER
13
F
IGURE 13.4
.
(
Continued
)
o
f segmental motor activities, for example, respiratory movements, walking, and flight.
Recentl
y
, the central bod
y
and the closel
y
associated
p
rotocerebral brid
g
e have been shown
to
p
ossess
p
o
l
ar
i
ze

d ligh
t-sens
i
t
i
ve
i
nterneurons, su
gg
est
i
n
g
aro
l
e
f
or t
h
ese centers
i
n
nav
ig
at
i
on (V
i
tzt
h

um
e
t al.
,
2002). Eac
h
o
p
t
i
c
l
o
b
e conta
i
ns t
h
ree neuro
pil
ar masses
i
n
w
hich light stimuli, including those generated by polarized light, are assessed and forwarde
d
to other brain centers.
T
he deutocerebrum is lar
g

el
y
com
p
osed of the
p
aired antennal lobes (Homber
g
et al
.
, 1989; Hannson an
d
Anton, 2000). T
h
ese two neuro
pil
es
i
nc
l
u
d
e
b
ot
h
sensor
y
an
d

motor neurons an
d
are res
p
ons
ibl
e
f
or
i
n
i
t
i
at
i
n
gb
ot
h
res
p
onses to antenna
l
st
i
mu
li
,es
p

e
-
ci
a
ll
yo
lf
actory an
d
mec
h
anosensory, an
d
movements o
f
t
h
e antennae. In spec
i
es w
h
ere
f
emales produce sex-pheromones the antennal lobes often show sexual dimorphism, being
l
ar
g
er with additional interneurons in males. From the antennal lobes, interneurons conve
y
4

1
1
NERV
O
U
S
AND
C
HEMI
CA
L
INTE
G
RATI
ON
i
nformation to association centers in both the protocerebrum and thoracic ganglia. Togethe
r
w
ith the mushroom bodies, the antennal lobes are essential in learned olfactor
y
behavior.
T
h
e trans
f
er o
f
mec
h

anosensor
yi
n
p
uts to t
h
e ventra
lg
an
gli
a
i
s
lik
e
ly
re
l
ate
d
to
p
erce
p
t
i
o
n
an
d

avo
id
ance o
f
o
bj
ects encountere
dd
ur
i
n
g
wa
lki
n
g.
T
h
etr
i
tocere
b
rum
i
s a sma
ll
reg
i
on o
f

t
h
e
b
ra
i
n
l
ocate
db
eneat
h
t
h
e
d
eutocere
b
rum an
d
comprises a pair of neuropiles that contain axons, both sensory and motor, leading to/fro
m
t
he frontal
g
an
g
lion and labrum
.
T

h
esu
b
eso
ph
a
g
ea
lg
an
gli
on
i
sa
l
so com
p
os
i
te an
di
nc
l
u
d
es t
h
ee
l
ements o

f
t
h
eem
b
r
y-
on
i
c
g
an
gli
ao
f
t
h
e man
dib
u
l
ar, max
ill
ar
y
,an
dl
a
bi
a

l
se
g
ments. From t
hi
s
g
an
gli
on, nerve
s
conta
i
n
i
ng
b
ot
h
sensory an
d
motor axons run to t
h
e mout
h
parts, sa
li
vary g
l
an

d
s, an
d
nec
k.
The ganglion also appears to be the center for maintaining (though not initiating) locomoto
r
activity
.
I
n most
i
nsects t
h
et
h
ree se
g
menta
l
t
h
orac
i
c
g
an
gli
a rema
i

nse
p
arate. T
h
ou
gh d
eta
ils
v
ar
yf
rom s
p
ec
i
es to s
p
ec
i
es, eac
hg
an
gli
on
i
nnervates t
h
e
l
e

g
an
d fligh
t musc
l
es (
di
rect an
d
i
n
di
rect), sp
i
rac
l
es, an
d
sense organs o
f
t
h
e segment
i
nw
hi
c
hi
t
i

s
l
ocate
d.
The maximum number of abdominal ganglia is eight, seen in the adult bristletai
l
M
ac
h
i
l
is and larvae of many species, though even in these insects the terminal ganglio
n
i
s com
p
osite, includin
g
the last four se
g
mental
g
an
g
lia of the embr
y
onic sta
g
e. Var
y

in
g
d
e
g
rees o
ff
us
i
on o
f
t
h
ea
bd
om
i
na
lg
an
gli
a occur
i
n
diff
erent or
d
ers an
d
somet

i
mes t
h
ere
is
f
us
i
on o
f
t
h
e compos
i
te a
bd
om
i
na
l
gang
li
on w
i
t
h
t
h
e gang
li

ao
f
t
h
et
h
orax to
f
ormas
i
ng
le
t
horacoabdominal ganglion. (Chapters
5
–10 contain the details for individual orders.
)
2
.2. Visceral Nervous S
y
stem
T
h
ev
i
scera
l
(s
y
m

p
at
h
et
i
c) nervous s
y
stem
i
nc
l
u
d
es t
h
ree
p
arts: t
h
e stomato
g
astr
ic
system, t
h
e unpa
i
re
d
ventra

l
nerves, an
d
t
h
e cau
d
a
l
sympat
h
et
i
c system. T
h
e stomatogastr
ic
system, shown partially in Figure 13.4, arises during embryogenesis as an invagination of
t
he dorsal wall of the stomodeum. Generall
y
, it includes the frontal
g
an
g
lion, recurrent nerv
e
whi
c
hli

es me
di
o
d
orsa
lly
a
b
ove t
h
e
g
ut,
hyp
ocere
b
ra
lg
an
gli
on, a
p
a
i
ro
fi
nner eso
ph
a
g

ea
l
n
erves, a
p
a
i
ro
f
outer eso
ph
a
g
ea
l
(
g
astr
i
c) nerves, eac
h
o
f
w
hi
c
h
norma
lly
term

i
nates
in
an
i
ng
l
uv
i
a
l
(ventr
i
cu
l
ar) gang
li
on s
i
tuate
d
a
l
ongs
id
et
h
e poster
i
or

f
oregut, an
d
var
i
ous fin
e
n
erves from these ganglia that innervate the foregut and midgut, and, in some species, th
e
h
eart. A single median ventral nerve arises from each thoracic and abdominal ganglion i
n
some insects. The nerve branches and innervates the s
p
iracle on each side. In s
p
ecie
s
wh
ere t
hi
s nerve
i
sa
b
sent,
p
a
i

re
dl
atera
l
nerves
f
rom t
h
ese
g
menta
lg
an
gli
a
i
nnervat
e
th
esp
i
rac
l
es. T
h
e cau
d
a
l
sympat

h
et
i
c system, compr
i
s
i
ng nerves ar
i
s
i
ng
f
rom t
h
e compos
i
t
e
t
erminal abdominal ganglion, innervates the hindgut and sexual organs. Nerves withi
n
t
he stomatogastric system both collect mechanosensory and chemical information from
,
and re
g
ulate the muscular activit
y
of, the or

g
ans the
y
su
pp
l
y
. In the frontal
g
an
g
lion, a
t
l
east, t
h
e neuro
pil
e
h
as a centra
lp
attern
g
enerator (Sect
i
on 2.3) t
h
at contro
l

sr
hy
t
h
m
ic
m
otor act
i
v
i
t
y
o
f
t
h
e
f
ore
g
ut (A
y
a
li
e
t al.
,
2002)
.

2
.3. Physiology of Neural Integration
As note
di
nt
h
e Intro
d
uct
i
on to t
hi
sc
h
a
p
ter, an
i
nsect’s nervous s
y
stem
i
s constant
ly
r
ece
i
v
i
n

g
st
i
mu
li
o
f diff
erent
ki
n
d
s
b
ot
hf
rom t
h
e externa
l
env
i
ronment an
df
rom w
i
t
hi
n
i
ts own

b
o
d
y. T
h
esu
b
sequent response o
f
t
h
e
i
nsect
d
epen
d
sont
h
e net assessment o
f
t
hese stimuli within the central nervous system. The processes of receiving, assessing, an
d
412
C
HAPTER
13
F
IGURE 1

3
.5.
C
ross-sect
i
on to s
h
ow ma
j
or areas o
fb
ra
i
n. [A
f
ter R. F. C
h
apman, 1971,
Th
e Insects:
S
tructure
a
n
d
Function
.
B
yp
erm

i
ss
i
on o
f
E
l
sev
i
er
/
Nort
h
-Ho
ll
an
d
, Inc., an
d
t
h
e aut
h
or.
]
respon
di
ng to st
i
mu

li
co
ll
ect
i
ve
l
y const
i
tute neura
li
ntegrat
i
on. Neura
li
ntegrat
i
on
i
nc
l
u
d
es,
therefore, the biophysics of impulse transmission along axons and across synapses, the refle
x
p
athways (in insects, intrasegmental) from sense organ to effector organ, and coordinatio
n
o

f these se
g
mental events within the central nervous s
y
stem.
Im
p
u
l
se transm
i
ss
i
on a
l
on
g
axona
l
mem
b
ranes an
d
across s
y
na
p
ses a
pp
ears to

b
e es-
sent
i
a
ll
yt
h
e same as
i
not
h
er an
i
ma
l
san
d
w
ill
not
b
e
di
scusse
dh
ere
i
n
d

eta
il
. However, t
h
e
absence of a myelin sheath and nodes of Ranvier precludes the phenomenon of saltatory
c
onduction seen in vertebrates. Following the arrival of a stimulus of sufficient magnitude,
an action
p
otential is
g
enerated and the im
p
ulse travels alon
g
the axon as a wave of de
-
p
o
l
ar
i
zat
i
on. T
h
es
p
ee

d
o
fi
m
p
u
l
se transm
i
ss
i
on
i
sa
f
unct
i
on o
f
axona
ldi
ameter so t
h
at
i
n
gi
ant axons va
l
ues o

f
3–7 m
p
er sec
h
ave
b
een recor
d
e
d
w
hil
e
i
n avera
g
e-s
i
ze
d
axon
s
the speed is 1.
5
–2.3 m per sec. In addition to “spiking” neurons (i.e., those in which a
n
action potential can be generated), there are in the insect central nervous system intragan
-
g

lionic “non-s
p
ikin
g
” interneurons unable to
p
roduce action
p
otentials. Rather, the amount
of
neurotransm
i
tter re
l
ease
d
at t
h
e
i
rs
y
na
p
ses (see
b
e
l
ow)
i

s
p
ro
p
ort
i
ona
l
to t
h
es
i
ze o
f
t
h
e
ir
en
d
o
g
enous mem
b
rane
p
ermea
bili
t
y

c
h
an
g
es;
i
not
h
er wor
d
s, t
h
e
y
re
l
ease neurotransm
i
tter
(an
d
a
ff
ect t
h
e postsynapt
i
c neuron)
i
n a gra

d
e
d
manner. T
h
ese non-sp
iki
ng
i
nterneuron
s
may have wide importance in the initiation of rhythmic behaviors such as walking, swim
-
min
g
, and chewin
g
(see below)
.
T
ransm
i
ss
i
on across a s
y
na
p
se,
d

e
p
en
di
n
g
as
i
t
d
oes on
diff
us
i
on o
f
mo
l
ecu
l
es t
h
rou
gh
fl
uid, is relativel
y
slow and ma
y
take u

p
about 25% of the total time for conduction of
an
i
mpu
l
se t
h
roug
h
are
fl
ex arc. Rare
l
y, w
h
en a synapt
i
c gap
i
s narrow (
i
.e., pre- an
d
p
ostsynaptic membranes are closely apposed), the ionic movements across the presynaptic
membrane are sufficient to directly induce depolarization of the postsynaptic membran
e
4
1

3
NERV
O
U
S
AND
C
HEMI
CA
L
INTE
G
RATI
ON
(
Huber, 1974). Mostly, however, when an impulse reaches a synapse, it causes release
of a chemical
(
a neurotransmitter
)
from membrane-bound vesicles. The chemical diffuses
across t
h
es
y
na
p
se an
d
,

i
nexc
i
tator
y
neurons,
b
r
i
n
g
sa
b
out
d
e
p
o
l
ar
i
zat
i
on o
f
t
h
e
p
osts

y
-
n
a
p
t
i
c mem
b
rane. Acet
yl
c
h
o
li
ne
i
st
h
e
p
re
d
om
i
nant neurotransm
i
tter
lib
erate

d
at exc
i
tator
y
synapes,
i
nc
l
u
di
ng t
h
ose o
fi
nterneurons an
d
a
ff
erent neurons
f
rom mec
h
anosens
ill
aan
d
t
aste sensilla (Homberg, 1994).
5

-Hydroxytryptamine (serotonin), histamine, octopamine,
and do
p
amine function as central nervous s
y
stem excitator
y
neurotransmitters in s
p
ecific
s
i
tuat
i
ons on occas
i
on. T
h
ese, an
d
ot
h
er am
i
nes,
h
aveanexc
i
tator
y

e
ff
ect w
h
en a
ppli
e
din
l
ow concentrat
i
ons to t
h
e
h
eart,
g
ut, re
p
ro
d
uct
i
ve tract, etc., an
di
tma
yb
et
h
at t

h
e
y
a
l
so
serve as neurotransm
i
tters
i
nt
h
ev
i
scera
l
nervous system.
S
ometimes a single nerve impulse arriving at the presynaptic membrane does not
stimulate the release of a sufficient amount of neurotransmitter. Thus, the magnitude o
f
d
e
p
o
l
ar
i
zat
i

on o
f
t
h
e
p
osts
y
na
p
t
i
c mem
b
rane
i
s not
l
ar
g
e enou
gh
to
i
n
i
t
i
ate an
i

m
p
u
l
se
in
th
e
p
osts
y
na
p
t
i
c axon. I
f
a
ddi
t
i
ona
li
m
p
u
l
ses reac
h
t

h
e
p
res
y
na
p
t
i
c mem
b
rane
b
e
f
ore t
he
first
d
epo
l
ar
i
zat
i
on
h
as
d
ecaye

d
,su
f
fic
i
ent a
ddi
t
i
ona
l
neurotransm
i
tter may
b
ere
l
ease
d
so
t
hat the minimum level for continued passage of the impulse (the “threshold” level) is ex-
ceeded. This additive effect of the presynaptic impulses is known as temporal summation
.
A second form of summation is s
p
atial, which occurs at conver
g
ent s
y

na
p
ses. Here, several
sensor
y
axons s
y
na
p
se w
i
t
h
one
i
nternunc
i
a
l
neuron. A
p
osts
y
na
p
t
i
c
i
m

p
u
l
se
i
s
i
n
i
t
i
ate
d
on
l
yw
h
en
i
mpu
l
ses
f
romasu
f
fic
i
ent num
b
er o

f
sensory axons arr
i
ve at t
h
e synapse s
i
-
m
ultaneously. Divergent synapses are also found where the presynaptic axon synapses with
several postsynaptic neurons. In this arrangement the arrival of a single impulse at a synapse
m
a
y
be sufficient to initiate im
p
ulse transmission in, sa
y
, one of the
p
osts
y
na
p
tic neurons
.
T
h
e arr
i

va
l
o
f
a
ddi
t
i
ona
li
m
p
u
l
ses
i
n
q
u
i
c
k
success
i
on w
ill l
ea
d
to t
h

e
i
n
i
t
i
at
i
on o
fi
m
p
u
l
ses
i
not
h
er
p
osts
y
na
p
t
i
c neurons w
h
ose t
h

res
h
o
ld l
eve
l
s are
high
er. T
h
us, s
y
na
p
ses
pl
a
y
a
n
i
mportant ro
l
e
i
nse
l
ect
i
on o

f
an appropr
i
ate response
f
orag
i
ven st
i
mu
l
us
.
Eventually, an impulse reaches the effector organ, most commonly muscle. Betwee
n
t
he ti
p
of the motor axon and the muscle cell membrane is a fluid-filled s
p
ace, com
p
arable t
o
a
sy
na
p
se, ca
ll

e
d
a neuromuscu
l
ar
j
unct
i
on. A
g
a
i
n, to ac
hi
eve
d
e
p
o
l
ar
i
zat
i
on o
f
t
h
e musc
le

ce
ll
mem
b
rane an
d
,u
l
t
i
mate
ly
, musc
l
e contract
i
on,ac
h
em
i
ca
l
re
l
ease
df
rom t
h
et
ip

o
f
t
h
e
axon
diff
uses across t
h
e neuromuscu
l
ar
j
unct
i
on. In
i
nsect s
k
e
l
eta
l
musc
l
e, t
hi
sc
h
em

i
ca
lis
L
-glutamate; in visceral muscles, glutamate, serotonin, and the pentapeptide proctolin have
all been suggested as candidate neurotransmitters.
I
n addition to stimulator
y
(excitator
y
) neurons, inhibitor
y
neurons whose neurotrans
-
mi
tter causes
hyp
er
p
o
l
ar
i
zat
i
on o
f
t
h

e
p
osts
y
na
p
t
i
core
ff
ector ce
ll
mem
b
rane are a
l
so
i
m
p
or
-
t
ant
i
n neura
li
ntegrat
i
on. W

h
en
i
n
hibi
t
i
on occurs at a synapse w
i
t
hi
nt
h
e centra
l
nervous sys
-
t
em, it is known as central inhibition. Central inhibition is the prevention of the normal stimu-
latory output from the central nervous system and may arise spontaneously within the system
or result from sensor
y
in
p
ut. For exam
p
le, co
p
ulator
y

movements of the abdomen in the mal
e
m
ant
i
s, w
hi
c
h
are re
g
u
l
ate
dby
ase
g
menta
l
re
fl
ex
p
at
h
wa
yl
ocate
d
w

i
t
hi
nt
h
e term
i
na
l
a
b
-
d
om
i
na
lg
an
gli
on, are norma
lly i
n
hibi
te
dby
s
p
ontaneous
i
m

p
u
l
ses ar
i
s
i
n
g
w
i
t
hi
nt
h
e
b
ra
in
and passing down the ventral nerve cord
.
In the fl
y
P
roto
ph
ormi
a
t
he stimulation of stretch

r
eceptors during feeding results in decreased sensitivity to taste caused by central inhibitio
n
of the
p
ositive stimuli received b
y
the brain from the tarsal chemorece
p
tors. When inhibitio
n
o
f
an e
ff
ector or
g
an occurs
i
t
i
s
k
nown as
p
er
iph
era
li
n

hibi
t
i
on. At
b
ot
h
s
y
na
p
ses an
d
neuro
-
m
uscu
l
ar
j
unct
i
ons, t
h
e
hyp
er
p
o
l

ar
i
z
i
n
g
c
h
em
i
ca
lis
γ
-
am
i
no
b
ut
y
r
i
cac
id
(Hom
b
er
g
, 1994)
.

M
ent
i
on must a
l
so
b
ema
d
eo
f
neuromo
d
u
l
ators, a group o
f
c
h
em
i
ca
l
st
h
at can
m
odify the effects of neurotransmitters (Orchard, 1984; Homberg, 1994). Typically,
41
4

C
HAPTER
13
neuromodulators are released from the tip of an adjacent neuron (less commonly as a
neurohormone released into the hemol
y
m
p
h) and act on the
p
res
y
na
p
tic or
p
osts
y
na
p
ti
c
mem
b
rane a
dj
acent to,
b
ut not w
i

t
hi
n, t
h
es
y
na
p
t
i
c
g
a
p
or neuromuscu
l
ar
j
unct
i
on. T
h
e
ir
e
ff
ects
i
nc
l

u
d
ere
d
uct
i
on
i
nt
h
e amount o
f
neurotransm
i
tter re
l
ease
d
an
di
n
hibi
t
i
on o
f
t
h
eac
-

t
i
on o
f
t
h
e neurotransm
i
tter. Am
i
nes, espec
i
a
ll
y octopam
i
ne, an
d
some neuropept
id
es (e.g.
,
p
roctolin) are likely to be important neuromodulators, though in many instances definitive
evidence is still lackin
g
.A
p
robable neuromodulator of a s
p

ecial kind ma
y
be nitric oxide.
Thi
sver
y
s
h
ort-
li
ve
d
,ra
pidly diff
us
i
n
gg
as was
di
scovere
di
n nervous t
i
ssues o
fl
ocusts
,
h
one

yb
ees, an
d
Droso
p
hil
a
i
nt
h
e ear
ly
1990s. Pro
d
uct
i
on o
f
n
i
tr
i
cox
id
e
i
ses
p
ec
i

a
lly
r
i
c
h
i
n
i
nterneurons
i
nt
h
e antenna
l
an
d
opt
i
c
l
o
b
es, as we
ll
as
i
n antenna
l
c

h
emosensory ce
ll
s
o
f some species, following appropriate olfactory and visual stimulation, suggesting that
this unconventional neuromodulator may have roles in olfactory information processing,
olf
actor
y
memor
y
,an
d
v
i
s
i
on (M¨u
ll
er, 1997; B
i
c
k
er, 1998).
In
i
nsects re
fl
ex res

p
onses are se
g
menta
l
,t
h
at
i
s,ast
i
mu
l
us rece
i
ve
dby
a sense or
g
a
n
i
n a part
i
cu
l
ar segment
i
n
i

t
i
ates a response t
h
at trave
l
sv
i
aan
i
nterneuron
l
ocate
di
nt
h
at
segment’s ganglion to an effector organ in the same segment. This is easily demonstrated b
y
isolating individual segments. For example, in an isolated thoracic segment preparation of
a
g
rassho
pp
er, touchin
g
the tarsus causes the le
g
to make a ste
pp

in
g
movement. Of course
,
i
nan
i
ntact
i
nsect suc
h
ast
i
mu
l
us a
l
so
l
ea
d
stocom
p
ensator
y
movements o
f
ot
h
er

l
e
g
sto
ma
i
nta
i
n
b
a
l
ance or to
i
n
i
t
i
ate wa
lki
ng, act
i
v
i
t
i
es t
h
at are coor
di

nate
d
v
i
a assoc
i
at
i
on centers
in the subesophageal ganglion. Touching the tip of the isolated ovipositor i
n
Bomby
x
,fo
r
e
xample, initiates typical egg-laying movements, provided that the terminal ganglion an
d
its nerves are intact. In other words, each se
g
mental
g
an
g
lion
p
ossesses a
g
ood deal of refle
x

au
t
onom
y
.
N
ervous act
i
v
i
t
y
o
f
t
h
et
yp
e
d
escr
ib
e
d
a
b
ove, w
hi
c
h

occurs on
ly
a
f
ter an a
pp
ro
p
r
i
at
e
st
i
mu
l
us
i
sg
i
ven,
i
ssa
id
to
b
e exogenous. However, an
i
mportant component o
f

nervous
activity in insects is endogenous, that is, does not require sensory input but is based o
n
neurons with intrinsic
p
acemakers. Such neurons (non-s
p
ikin
g
neurons)
p
ossess s
p
ecialized
mem
b
rane re
gi
ons t
h
at un
d
er
g
o
p
er
i
o
di

c, s
p
ontaneous c
h
an
g
es
i
nexc
i
ta
bili
t
y
(
p
ermea
bili
t
y
)
an
d
w
h
ere
i
m
p
u

l
ses are t
h
ere
by i
n
i
t
i
ate
d
.Aw
id
evar
i
et
y
o
f
motor res
p
onses are or
g
an
i
ze
d,
i
n part,
b

yen
d
ogenous act
i
v
i
ty. For examp
l
e, vent
il
at
i
on movements o
f
t
h
ea
bd
omen are
initiated by endogenous activity in individual ganglia. Even walking and stridulation ar
e
motor responses under partially endogenous control (Huber, 1974). An obvious question
to ask, therefore, is “Wh
y
don’t insects walk or stridulate continuousl
y
?” The answer i
s
t
h

at t
h
ese an
d
a
ll
ot
h
er motor res
p
onses are “contro
ll
e
d
”
by high
er centers, s
p
ec
i
fica
lly
t
h
e
b
ra
i
nan
d/

or su
b
esop
h
agea
l
gang
li
on. T
h
ese assoc
i
at
i
on centers assess a
ll i
n
f
ormat
i
o
n
c
oming in via sensory neurons and, on this total assessment, determine the nature of the
response. In addition, the centers coordinate and modify identical segmental activities
,
such as ventilation movements, so that the
y
o
p

erate most efficientl
y
under a
g
iven set of
c
on
di
t
i
ons
.
E
ar
ly
ev
id
ence
f
or t
h
ero
l
eo
f
t
h
e
b
ra

i
nan
d
su
b
eso
ph
a
g
ea
lg
an
gli
on as coor
di
nat
i
n
g
c
enters came from fairly crude experiments in which one or both centers were removed and
the resultant behavior of an insect observed. More recent experiments involving localized
destruction or stimulation of
p
arts of these centers have confirmed and added si
g
nificantl
y
to t
h

e
g
enera
lpi
cture o
b
ta
i
ne
dby
ear
li
er aut
h
ors. To
ill
ustrate t
h
e com
pl
ex
i
t
y
o
f
coor
di-
nat
i

on an
d
contro
l
o
f
motor act
i
v
i
t
y
,wa
lki
n
g
w
ill b
e use
d
as an exam
pl
e. T
hi
sr
hy
t
h
m
ic

stepp
i
ng movement o
f
eac
hl
eg
i
s contro
ll
e
db
y a networ
k
o
f
non-sp
iki
ng neurons (ca
ll
e
d
the central pattern generator and located in each half ganglion) whose endogenous activit
y
4
15
NERV
O
U
S

AND
C
HEMI
CA
L
INTE
G
RATI
ON
sends signals (via motor neurons) alternately to the extensor and flexor leg muscles (Chap-
t
er 14, Section 3.2.1). The si
g
nals ma
y
be excitator
y
or inhibitor
y
and, in effect, serve t
o
sw
i
tc
h
on or o
ff
t
h
e musc

l
es. Intra
g
an
gli
on
i
can
di
nterse
g
menta
l
coor
di
nat
i
on amon
g
t
he
centra
lp
attern
g
enerators, an
d
u
l
t

i
mate
ly l
e
g
movements,
i
sac
hi
eve
d
v
i
a norma
li
nterneu-
r
ons. T
hi
s
i
s rea
dil
ys
h
own
b
y cutt
i
ng even one connect

i
ve o
f
t
h
epa
i
r
b
etween a
dj
acent
g
anglia when coordinated stepping is disrupted. Though the overall control of walking, tha
t
i
s, startin
g
, sto
pp
in
g
, turnin
g
, and chan
g
eofs
p
eed, resides in the brain, the subeso
p

ha
g
eal
g
an
gli
on
i
sa
l
so
i
nvo
l
ve
d
. Remova
l
o
f
t
h
e
l
atter,
f
or exam
pl
e, sens
i

t
i
zes some
i
nsects so t
h
a
t
th
e
y
wa
lk i
ncessant
ly i
n res
p
onse to even s
ligh
tst
i
mu
li
.Int
h
e
b
ra
i
nt

h
e mus
h
room
b
o
di
e
s
an
d
centra
lb
o
d
yp
l
ay ma
j
or ro
l
es
i
nt
h
eregu
l
at
i
on o

f
wa
lki
ng. Impu
l
ses or
i
g
i
nat
i
ng
i
nt
he
m
ushroom bodies inhibit locomotor activity, presumably by decreasing the excitability o
f
t
he subesophageal ganglion. Moreover, reciprocal inhibition may occur between the mush
-
r
oom
b
o
dy
on eac
h
s
id

eo
f
t
h
e
b
ra
i
n, an
d
t
hi
s
i
st
h
e
b
as
i
so
f
t
h
e turn
i
n
g
res
p

onse. In contrast
,
th
e centra
lb
o
dy
a
pp
ears to
b
ean
i
m
p
ortant exc
i
tator
y
s
y
stem
i
n
l
ocomot
i
on,
b
ecause

i
t
s
st
i
mu
l
at
i
on evo
k
es
f
ast runn
i
ng,
j
ump
i
ng, an
dfl
y
i
ng
i
n some spec
i
es. As yet,
h
owever, t

he
i
nteraction between these two cerebral association centers is not understood
.
S
uperimposed on the central control of walking is the influence of sensory stimul
i
r
eceived b
y
the insect; that is, the insect ad
j
usts its walkin
gp
attern to suit environmental
con
di
t
i
ons suc
h
as movement u
phill
or
d
own
hill
,a
l
on

g
as
l
o
p
e, or over rou
gh
terra
i
n. To
thi
sen
d
,t
h
e
l
egs are equ
i
ppe
d
w
i
t
h
avar
i
ety o
f
mec

h
anoreceptors t
h
at prov
id
e
i
n
f
ormat
i
on
on their position, loading, and movement (Chapter 12, Section 2). In a walking Colorad
o
potato beetle, contact between the antennae and an obstacle causes the insect to modify its
b
od
y
an
g
le. The extent to which the bod
y
an
g
le is chan
g
ed is
p
ro
p

ortional to the hei
g
ht
o
f
t
h
eo
b
stac
l
e, a
ll
ow
i
n
g
t
h
e
b
eet
l
e to exten
d
t
h
e reac
h
o

f
t
h
e
p
rot
h
orac
i
c
l
e
g
so as to ste
p
up
on to t
h
eo
b
stac
l
e. Insects t
h
at use runn
i
n
g
to esca
p

e
p
re
d
ators rece
i
ve
i
n
f
ormat
i
on v
i
a
ot
h
er sensory pat
h
ways. For examp
l
e,
i
nt
h
e coc
k
roac
h
escape react

i
on, even t
h
es
li
g
h
test
air movements stimulate hairs on the cerci that are both velocity- and direction-sensitive
.
The information received travels via
g
iant axons in the ventral nerve cord to the thoraci
c
g
an
g
lia to initiate both the runnin
g
and the turnin
g
awa
y
res
p
onses within 0.5 msec of th
e
st
i
mu

l
us
b
e
i
n
g
rece
i
ve
d
.
At t
h
e outset,
i
nsect
b
e
h
av
i
or
i
s
d
epen
d
ent on t
h

eenv
i
ronmenta
l
st
i
mu
li
rece
i
ve
d,
t
hough, as noted earlier, not all behavior patterns originate exogenously; many common
patterns have a spontaneous, endogenous origin. Axons may be branched; synapses may b
e
conver
g
ent or diver
g
ent; tem
p
oral or s
p
atial summation of im
p
ulses ma
y
occur at s
y

na
p
ses;
n
eurons ma
yb
eexc
i
tator
y
or
i
n
hibi
tor
yi
nt
h
e
i
re
ff
ects. T
h
us, an enormous num
b
er o
f
potent
i

a
l
routes are open to
i
mpu
l
ses generate
db
yag
i
ven set o
f
st
i
mu
li
.T
h
e eventua
l
r
outes taken and, therefore, the motor responses that follow, depend on the size, nature, an
d
frequency of these stimuli
.
2
.4. Learning and Memor
y
T
h

e trans
l
at
i
on o
f
sensory
i
nput
i
nto a motor response ta
k
es p
l
ace w
i
t
hi
n a matter o
f
m
illiseconds and thereby fits well into the broad definition of “nervous control.” However,
another im
p
ortant as
p
ect of neural
p
h
y

siolo
gy
is learnin
g
, which, alon
g
with the relate
d
ev
e
nt, memor
y
,ma
y
occu
py
t
i
me
i
nterva
l
s measure
di
n
h
ours,
d
a
y

s, or even
y
ears. Learn
i
n
g
i
st
h
ea
bili
t
y
to assoc
i
ate one env
i
ronmenta
l
con
di
t
i
on w
i
t
h
anot
h
er; memor

yi
st
h
ea
bili
t
y
t
o store
i
n
f
ormat
i
on gat
h
ere
db
y sense organs. W
i
t
hi
nt
hi
s
b
roa
dd
efin
i

t
i
on o
fl
earn
i
ng
,
several phenomena can be included. Habituation, perhaps the simplest form of learning, is
41
6
C
HAPTER
13
adaptation (eventual failure to respond) of an organism to stimuli that are not significant t
o
its well-bein
g
. For exam
p
le, as noted above, a cockroach normall
y
shows a strikin
g
esca
p
e
react
i
on w

h
en a
i
r
i
s
bl
own over t
h
e cerc
i
.I
f
,
h
owever, t
hi
s treatment
i
s cont
i
nue
df
or a
p
er
i
o
d
of

t
i
me, t
h
e
i
nsect eventua
lly
no
l
on
g
er res
p
on
d
sto
i
t. Con
di
t
i
on
i
n
gi
s
l
earn
i

n
g
to res
p
on
d
toast
i
mu
l
us t
h
at
i
n
i
t
i
a
ll
y
h
as no e
ff
ect. Re
l
ate
d
to t
hi

s
i
str
i
a
l
-an
d
-error
l
earn
i
ng w
h
ere
an animal learns to respond in a particular way to a stimulus, having initially attempted to
res
p
ond in other wa
y
s for which acts it received a ne
g
ative reaction
.
Th
e most com
pl
ex
f
orm o

fl
earn
i
n
gi
n
i
nsects,
l
atent
l
earn
i
n
g
,
i
st
h
ea
bili
t
y
to re
l
at
e
two or more env
i
ronmenta

l
st
i
mu
li
,t
h
ou
gh
t
hi
s
d
oes not con
f
er an
i
mme
di
ate
b
enefit. For
i
nsects, v
i
sua
l
an
d
c

h
emosensory (espec
i
a
ll
yo
lf
actory) cues are espec
i
a
ll
y
i
mportant
i
n
l
atent learning. For example, Micro
pl
itis
s
pp. learn to associate color, shape, and patter
n
w
ith successful oviposition;
L
ocust
a
a
ssociates odor or visual cues with food quality; and

mos
q
u
i
toes
l
earn to reco
g
n
i
ze (an
d
return to) s
i
tes w
h
ere t
h
e
yh
ave success
f
u
lly f
e
d
an
d/
o
r

o
v
ip
os
i
te
d
(McCa
ll
an
d
Ke
lly
, 2002). Per
h
a
p
st
h
e
b
est-stu
di
e
d
exam
pl
eo
fl
atent

l
earn
i
n
gi
s
t
h
e recogn
i
t
i
on an
d
use o
fl
an
d
mar
k
s
b
y soc
i
a
l
Hymenoptera, ena
bli
ng t
h

ese
i
nsects to return
to their nest or a food source. Foraging honey bees, wasps, and ants, on leaving a newly
discovered food source, undertake a series of “turn-back-and-look”
(
TBL
)
manoeuvre
s
(Lehrer, 1991; Judd and Collett, 1998; Lehrer and Bianco, 2000). In this activit
y
the insect,
wh
en
j
ust a
f
ew cent
i
meters
f
rom t
h
e
f
oo
d
source, re
p

eate
dly
turns an
dl
oo
k
s
b
ac
k
at
i
t.
Lik
ew
i
se,
i
nexper
i
ence
d
wor
k
ers carry out s
i
m
il
ar
l

earn
i
ng
fli
g
h
ts on first
l
eav
i
ng t
h
e nest
to forage. It has been proposed that the TBL activity enables the insect to take a series o
f
“snapshots” of the landmarks adjacent to the food source or nest. These pictures, memorized
w
ithin the o
p
tic lobes, are then matched with the current ima
g
e seen on the next tri
p
. When
t
h
e matc
hi
s “exact,” t
h

e
i
nsect
h
as reac
h
e
di
ts
g
oa
l
.
As note
d
,t
h
e TBL met
h
o
df
ac
ili
tates “c
l
ose-u
p
”
l
an

d
mar
k
reco
g
n
i
t
i
on. However, reco
g
-
n
i
t
i
on o
fl
an
d
mar
k
s
i
so
f
ten a
l
so use
d

as
i
nsects move
b
etween t
h
e nest an
d
a
f
oo
d
source
.
Fo
re
x
ample, insects may learn to steer to one side of a landmark to stay on the correct
p
ath; the
y
ma
yg
o directl
y
over landmarks that are on the fli
g
ht
p
ath; and b

y
reco
g
nizin
g
(matc
hi
n
g
) a scene, t
h
e
y
are a
bl
etocom
p
ensate
f
or unex
p
ecte
ddi
s
pl
acement o
f
t
h
e

i
r
p
o
-
s
i
t
i
on
p
rov
id
e
d
t
h
at t
h
e
yh
ave ex
p
er
i
ence
d
t
h
e “new”

p
os
i
t
i
on at a
p
rev
i
ous
p
o
i
nt
i
nt
i
m
e
(Co
ll
ett, 199
6
).
It is not always possible to use landmark recognition to navigate between nest an
d
f
ood source as the terrain may be featureless. Under such conditions, path integration is
em
p

lo
y
ed (Collett and Collett, 2000). Essentiall
y
,
p
ath inte
g
ration re
q
uires that an insec
t
h
as t
h
ea
bili
t
y
to mon
i
tor an
d
recor
d
c
h
an
g
es

i
n
i
ts
p
os
i
t
i
on over t
i
me, t
h
at
i
s, to measure
di
stance trave
l
e
d
, spee
d
o
f
trave
l
,an
ddi
rect

i
on trave
l
e
d
.T
h
e
i
nsect must t
h
en compute t
hi
s
information to set (or reset) a course toward the nest or food source. For many insects, path
integration incorporates the insect’s ability to navigate using polarized light (Chapter 12
,
Section 7.1.4), includin
g
a mechanism for measurin
g
and com
p
ensatin
g
for ela
p
sed time,
necess
i

tate
dby
t
h
e sun’s ever-c
h
an
gi
n
gp
os
i
t
i
on.
C
i
rca
di
an r
hy
t
h
ms are a
l
so a
f
orm o
fl
earn

i
n
g
. Man
y
or
g
an
i
sms
p
er
f
orm
p
art
i
cu
l
a
r
activities at set times of the day, and these activities are initially triggered by a certai
n
environmental stimulus, for example, the onset of darkness. Even if this stimulus is removed
,
b
y
kee
p
in

g
an animal in constant li
g
ht or dark, the activit
y
continues to be initiated at th
e
norma
l
t
i
me
.
Th
ou
gh
t
h
ere
i
sno
d
ou
b
tt
h
at
i
nsects are a
bl

e
b
ot
h
to
l
earn an
d
to memor
i
ze, t
he
ph
ys
i
o
l
og
i
ca
l/
mo
l
ecu
l
ar
b
as
i
s

f
or t
h
ese events
i
s not
k
nown. However, some genera
li
ze
d
statements can be made. The mushroom bodies are the center where complex behavior i
s
4
17
NERV
O
U
S
AND
C
HEMI
CA
L
INTE
G
RATI
ON
learned, and, these structures occupy a relatively greater proportion of the brain volume i
n

i
nsects such as the social H
y
meno
p
tera (
p
articularl
y
the worker caste), which exhibit th
e
g
reatest
l
earn
i
n
g
ca
p
ac
i
t
y
.A
g
rou
p
o
fp

acema
k
er ce
ll
s res
p
ons
ibl
e
f
or t
h
e
g
enerat
i
on o
f
c
i
rca
di
an r
h
yt
h
ms
in
Droso
p

hil
a
h
ave
b
een
id
ent
i
fie
di
nt
h
e centra
lb
ra
i
n (Saun
d
ers, 1997)
.
There is evidence that simpler forms of learning can occur in other ganglia, for example
,
t
hose of the thorax. Headless insects and even individual, isolated thoracic ganglia prepa
-
r
ations can learn to kee
p
ale

g
in a certain
p
osition so as to avoid re
p
eated electric shocks.
I
ntact an
i
ma
l
s reta
i
nt
hi
sa
bili
t
yf
or severa
ld
a
y
sa
f
ter t
h
e tra
i
n

i
n
gp
er
i
o
d
w
h
ereas
i
n
h
ea
dl
es
s
i
nsects t
h
e retent
i
on t
i
me
i
son
ly
1–2
d

a
y
s. However, su
b
se
q
uent remova
l
o
f
t
h
e
h
ea
d
o
f
i
nsects that have learned while intact does not reduce retention time, suggesting that intac
t
animals learn more readily than headless ones or isolated ganglia. A variety of pharmaco
-
lo
g
ical ex
p
eriments have been undertaken in attem
p
ts to establish the molecular basis of

l
earn
i
n
g
an
d
memor
y
,
i
nc
l
u
di
n
g
a
ppli
cat
i
on o
fp
rote
i
nornuc
l
e
i
cac

id
s
y
nt
h
es
i
s-
i
n
hibi
t
i
n
g
d
ru
g
s, assa
y
so
fp
rote
i
nan
d
nuc
l
e
i

cac
id
s
y
nt
h
es
i
s
i
n
g
an
gli
a
b
e
f
ore an
d
a
f
ter tra
i
n
i
n
g,
m
easurement o

f
c
h
o
li
nesterase
l
eve
l
s, an
d
app
li
cat
i
on o
f
cyc
li
c AMP
i
n
hibi
tors. However,
t
he results obtained are sometimes conflicting and difficult to interpret (see Eisenstein and
R
ee
p
, in Kerkut and Gilbert, 1985).

3
. Endocrine
Sy
ste
m
I
nsects, like vertebrates, possess both epithelial endocrine glands (the corpora allata an
d
m
o
l
t
gl
an
d
s,
d
er
i
ve
dd
ur
i
n
g
em
b
r
y
o

g
enes
i
s
f
rom
g
rou
p
so
f
ecto
d
erma
l
ce
ll
s
i
nt
h
ere
gi
on o
f
th
e max
ill
ar
yp

ouc
h
es) an
dgl
an
d
u
l
ar nerve ce
ll
s (neurosecretor
y
ce
ll
s), w
hi
c
h
are
f
oun
di
n
a
ll
gang
li
ao
f
t

h
e centra
l
nervous system an
di
n parts o
f
t
h
ev
i
scera
l
nervous system. T
h
e
ir
axons terminate in storage and release sites (neurohemal organs) or run directly to thei
r
t
arget organ. In addition, the gonads and some other structures of certain species produc
e
h
ormones
.
T
h
e
f
unct

i
ons o
fh
ormones are man
y
,an
ddi
scuss
i
on o
f
t
h
ese
i
s
b
est treate
di
n con-
j
unct
i
on w
i
t
h
spec
i
fic p

h
ys
i
o
l
og
i
ca
l
systems. In t
hi
sc
h
apter, t
h
ere
f
ore, on
l
yt
h
e structur
e
o
f the glands, the nature of their products, and the principles of neuroendocrine integration
w
ill be examined.
3
.1. Neurosecretor
y

Cells and Corpora Cardiac
a
The best-studied neurosecretory cells are the median neurosecretory cells (
m
N
SC) of
t
he protocerebrum. They occur in two groups, one on each side of the midline, and their axons
(
which form the NCC I)
p
ass down throu
g
h the brain, crossin
g
over en route, and normall
y
t
erm
i
nate
i
na
p
a
i
ro
f
neuro
h

ema
l
or
g
ans, t
h
e cor
p
ora car
di
aca, w
h
ere neurosecret
i
on
is
store
d
(F
ig
ure 13.4). In some s
p
ec
i
es,
f
or exam
pl
e,
M

u
s
ca d
o
me
s
tic
a
,
some neurosecre
t
or
y
axons
d
o not term
i
nate
i
nt
h
e corpora car
di
aca
b
ut pass t
h
roug
h
t

h
em to t
h
e corpora a
ll
ata. I
n
m
any Hemiptera-Heteroptera, the axons bypass the corpora cardiaca and, instead, terminat
e
i
n the ad
j
acent aorta wall. In a
p
hids, some neurosecretor
y
axons trans
p
ort their
p
roduct
di
rect
ly
to t
h
e tar
g
et or

g
an. An
d
t
h
e axons o
f
t
he
m
N
SC w
hi
c
hp
ro
d
uce
b
urs
i
con term
i
nate
i
n
th
e
f
use

d
t
h
oracoa
bd
om
i
na
lg
an
gli
on o
f high
er D
ip
tera an
di
nt
h
e
l
ast a
bd
om
i
na
lg
an
gli
on o

f
coc
k
roac
h
es an
dl
ocusts (H
i
g
h
nam an
d
H
ill
, 1977). T
h
e corpora car
di
aca are c
l
ose
l
y appose
d
t
o the dorsal aorta into which neurosecretion and intrinsic products of the corpora cardiaca
are released when the neurosecretory cell membranes are depolarized. The NCC I als
o
41

8
C
HAPTER
13
c
ontain ordinary neurons that innervate the intrinsic cells of the corpora cardiaca (see below)
,
c
ausin
g
them to release their
p
roduct. More than 40
y
ears a
g
o, it was noted that differen
t
m
N
SC ta
k
eu
p
c
h
aracter
i
st
i

c sta
i
ns. Furt
h
er,
d
estruct
i
on o
f
t
h
ece
ll
sa
ff
ects a w
id
e ran
g
e
of phy
s
i
o
l
o
gi
ca
lp

rocesses (see
l
ater c
h
a
p
ters),
l
ea
di
n
g
to t
h
e
p
ro
p
osa
l
t
h
at t
h
e
yp
ro
d
uc
e

av
a
r
i
ety o
fh
ormones. T
hi
s was confirme
d
t
h
roug
h
t
h
e use o
fi
mmuno
hi
stoc
h
em
i
stry,
f
ollowing purification of specific neurosecretory hormones. Also in the protocerebrum ar
e
two
g

rou
p
s of lateral neurosecretor
y
cells (
l
NSC
)
whose axons do not cross but travel to
t
h
e cor
p
us car
di
acum o
f
t
h
e same s
id
e. However, t
h
ere
i
sa
l
most no
i
n

f
ormat
i
on on t
h
e
i
r
f
unct
i
on
.
Th
e corpora car
di
aca ar
i
se as
i
nvag
i
nat
i
ons o
f
t
h
e
f

oregut
d
ur
i
ng em
b
ryogenes
i
satt
h
e
same time as the stomatogastric nervous system and are, in fact, modified nerve ganglia
.
T
hough their main function is to store neurosecretion, many of their intrinsic cells als
o
p
ro
d
uce
h
ormones. In some s
p
ec
i
es,
f
or exam
pl
e, t

h
e
d
esert
l
ocust, t
h
e neurosecretor
y
stora
g
e zone an
dgl
an
d
u
l
ar zone (zone o
fi
ntr
i
ns
i
cce
ll
s) are
di
st
i
nct (F

ig
ure 13.4C–E);
in
o
t
h
ers, t
h
e neurosecretory axons term
i
nate among t
h
e
i
ntr
i
ns
i
cce
ll
s.
N
eurosecretory cells are also found in all of the ventral ganglia, and their axons, whic
h
c
ontain stainable droplets, can be traced to a series of segmental neurohemal organs, th
e
p
eris
y

m
p
athetic or
g
ans ad
j
acent to the un
p
aired ventral nerve. In addition, there are man
y
re
p
orts o
f
mu
l
t
ip
o
l
ar neurosecretor
y
ce
ll b
o
di
es
lyi
n
g

on
p
er
iph
era
l
nerves
i
nnervat
i
n
g
t
h
e
h
eart, gut, etc. However,
i
ts
h
ou
ld b
e note
d
t
h
at,
f
or
b

ot
h
t
h
e neurosecretory ce
ll
so
f
t
h
e
v
e
ntral ganglia and those associated with peripheral nerves, only rarely has experimenta
l
evidence for their function been obtained
.
Man
y
functions have been ascribed to neurosecretor
y
hormones and the intrinsic hor
-
mones
p
ro
d
uce
dby
t

h
e cor
p
ora car
di
aca,
b
ut
f
or re
l
at
i
ve
ly f
ew o
f
t
h
ese
i
st
h
ere
g
oo
d
ex
p
er

i-
menta
l
ev
id
ence
.
Pro
d
ucts o
f
t
he
m
NSC
i
nc
l
u
d
e
p
rot
h
orac
i
cotro
pi
c
h

ormone (PTTH), w
hi
c
h
act
i
vates t
h
emo
l
tg
l
an
d
s(C
h
apter 21, Sect
i
on
6
.1); a
ll
atotrop
i
can
d
a
ll
atostat
i

c
h
ormones,
whose primary function is to regulate the activity of the corpora allata (Chapter 19, Sec-
tion 3.1.3 and Cha
p
ter 21, Section 6.1); diuretic hormone, which affects osmore
g
ulation
(Cha
p
ter 18, Section 5); ovarian ecd
y
siotro
p
ic hormone (OEH) (formerl
y
e
gg
develo
p
men
t
neurosecretor
yh
ormone) (C
h
a
p
ter 19, Sect

i
on 3.1.3); ovu
l
at
i
on- or ov
ip
os
i
t
i
on-
i
n
d
uc
i
n
g
hormone (Chapter 19, Sections
5
and 7.2); and testis ecdysiotropin (TE) (Chapter 19, Sec-
tion 3.2). Bursicon, which is important in cuticular tanning (Chapter 11, Section 3.4), has
been localized in the mNSC in some species, though is principally found in the abdom-
inal
g
an
g
lia from which it is released via abdominal
p

erivisceral or
g
ans. Neurosecretio
n
f
r
o
m
the
m
NSC a
l
so a
ff
ects
b
e
h
av
i
or, t
h
ou
gh i
n man
y
cases t
hi
s
i

s certa
i
n
ly
an
i
n
di
rec
t
act
i
on, an
di
s
i
mportant
i
n prote
i
n synt
h
es
i
s. Ec
l
os
i
on
h

ormone (EH),
i
mportant
i
nec
d
ys
i
s
(Chapter 21, Section 6.2), is produced by neurosecretory cells in the tritocerebrum. Th
e
intrinsic cells of the corpora cardiaca produce hyperglycemic and adipokinetic hormone
s
(AKH) im
p
ortant in carboh
y
drate and li
p
id metabolism (Cha
p
ter 16, Sections 5.2 and 5.3
)
an
dh
ormones t
h
at st
i
mu

l
ate
h
eart
b
eat rate (C
h
a
p
ter 17, Sect
i
on 3.2),
g
ut
p
er
i
sta
l
s
i
s, an
d
wr
i
t
hi
n
g
movements o

f
Ma
lpighi
an tu
b
u
l
es. It a
pp
ears,
h
owever, t
h
at t
h
e mNSC ma
yb
e
involve
d
in the elaboration of these materials because extracts of these cells exert simi
-
l
ar, though less strong, effects on these processes. Neurosecretion from the subesophageal
g
an
g
lion is, in cockroaches, s
y
nthesized and released re

g
ularl
y
and controls the circadia
n
r
hy
t
h
mo
fl
ocomotor act
i
v
i
t
y
.Inman
yf
ema
l
e mot
h
s,
ph
eromone
bi
os
y
nt

h
es
i
s act
i
vat
i
n
g
neuro
p
e
p
t
id
e (PBAN) (Sect
i
on 4.1)
i
s
p
ro
d
uce
di
nt
h
ree
g
rou

p
so
f
neurosecretor
y
ce
ll
s
i
n
t
h
esu
b
esop
h
agea
l
gang
li
on (
i
n some spec
i
es a
l
so ot
h
er ventra
l

gang
li
a). T
h
ePBANsyn
-
thesized in the subesophageal ganglion appears to be released via the corpora cardiaca. I
n
4
1
9
NERV
O
U
S
AND
C
HEMI
CA
L
INTE
G
RATI
ON
FI
G
URE 13.6
.
(
A) Locust

j
uven
il
e
h
ormone (C
1
6
J
H
=
JHIII
)
;an
d(
B
)
β
-ec
dy
sone.
female pupae
*
of
B
ombyx
,
t
wo large neurosecretory cells in the subesophageal ganglio
n

produce a diapause hormone which promotes the development of eggs that enter diapause
(
see C
h
a
p
ter 22, Sect
i
on 3.2.3). I
n
Rhodnius,
di
uret
i
c
h
ormone
i
s
p
ro
d
uce
d
not
by
t
h
e cere-
b

ra
l
neurosecretor
y
ce
ll
s
b
ut
by
t
h
e
hi
n
d
most
g
rou
p
o
f
neurosecretor
y
ce
ll
s
i
nt
h

e
f
use
d
g
ang
li
on o
f
t
h
et
h
orac
i
can
d
first a
bd
om
i
na
l
segments
.
All neurosecretory factors characterized to date are peptides (sometimes glycosylated)
,
an observation that is entirely in keeping with those from other animals. They range i
n
m

olecular wei
g
ht from the tens of thousands down to a thousand or less. Exam
p
les are bur
-
sicon (M.W. about 40,000), diuretic hormone (M.W. 1500–2000), OEH (6500), TE (2500),
d
ia
p
ause hormone (2
5
00), and AKH (a deca
p
e
p
tide). The PTTH of
D
roso
p
hila
i
sa
gly
-
cosylated polypeptide (M.W. 66,000). Curiously, the moth Man
d
uca
s
ext

a
produces two
forms of PTTH: the smaller form
(
M.W. 7000
)
comes from th
e
m
N
SC, whereas the larger
form (M.W. 28,000) is a
p
roduct of th
e
l
NSC. The two forms have
q
uite different structures,
y
et
i
n
l
arvae are a
b
out e
q
ua
lly

act
i
ve
.
3
.2.
C
orpora Allat
a
T
yp
icall
y
the cor
p
ora allata are seen as a
p
air of s
p
herical bodies l
y
in
g
one on each
s
id
eo
f
t
h

e
g
ut,
b
e
hi
n
d
t
h
e
b
ra
i
n(F
ig
ure 13.4A,B). However,
i
n some s
p
ec
i
es, t
h
e
gl
an
ds
m
a

yb
e
f
use
di
nam
idd
orsa
lp
os
i
t
i
on a
b
ove t
h
e aorta, or eac
hgl
an
d
ma
yf
use w
i
t
h
t
h
e

corpus car
di
acum on t
h
e same s
id
e. In
l
arvae o
f
cyc
l
orr
h
ap
h
D
i
ptera t
h
e corpora a
ll
ata,
corpora cardiaca, and molt glands fuse to form a composite structure, Weismann’s ring,
w
hich surrounds the aorta. Each
g
land receives a nerve (NCA I) from the cor
p
us cardiacu

m
o
n
i
ts own s
id
e, t
h
ou
gh
t
h
e axons t
h
at
f
orm t
hi
s nerve are
p
ro
b
a
bly
t
h
ose o
f
m
NSC

,
an
d
a
l
so a nerve
f
rom t
h
esu
b
eso
ph
a
g
ea
lg
an
gli
on (NCA II)
.
T
h
e corpora a
ll
ata pro
d
uce a
h
ormone

k
nown var
i
ous
l
yas
j
uven
il
e
h
ormone
,
m
etamorphosis-inhibiting hormone, or neotenin, with reference to its function in juve
-
nile insects (Chapter 21, Section 6.1), and gonadotropic hormone to indicate its function
i
n adults (Cha
p
ter 19, Sections 3.1.3 and 3.2). Juvenile hormone is a ter
p
enoid com
p
ound
(
F
ig
ure 13.
6

A) an
d
,to
d
ate, s
i
x natura
lly
occurr
i
n
gf
orms (JH-O, JH-I, 4-met
hyl
-JH-I
,
JH-II
,
JH-III
,
an
d
JH
B
3
)
h
a
v
e

been identified. In all insects investigated, except Hemiptera
,
L
epidoptera, and higher Diptera, only JH-III has been obtained. Though JH-III is reputedly
s
y
nthesized in some Hemi
p
tera, Numata et a
l
. (1992) re
p
ort that JH-I is the onl
y
for
m
p
ro
d
uce
di
nt
h
e
b
ean
b
u
g,
R

iptortus clavatus.
I
nLe
pid
o
p
tera t
h
e first five
f
orms o
f
JH
li
ste
d
*
In man
y
Le
pid
o
p
tera,
i
nc
l
u
di
n

g
B
om
byx
,e
gg d
eve
l
o
p
ment
b
e
gi
ns
i
nt
h
e
p
u
p
a.
42
0
C
HAPTER
13
above occur, with one or two forms predominating at specific stages in the life history. In
cy

clorrha
p
hDi
p
tera JHB
3
i
s the
p
rinci
p
al or sole
j
uvenile hormone, with JH-III occurrin
g
asam
i
nor com
p
onent
i
n some s
p
ec
i
es (Le
f
ever
e
e

tal
.
, 1993). In a
ddi
t
i
on, a
l
ar
g
e num
b
er
of
re
l
ate
d
com
p
oun
d
s
h
ave
b
een s
h
owntoexert
j

uven
ili
z
i
n
g
an
d/
or
g
ona
d
otro
pi
ce
ff
ects.
C
urrently, there is much interest in such compounds in view of their potential use in pest
c
ontrol (Chapter 24, Section 4.2).
3
.
3
. Molt Gland
s
Th
epa
i
re

d
mo
l
tg
l
an
d
s genera
ll
y compr
i
se two str
i
ps o
f
t
i
ssue,
f
requent
l
y
b
ranc
h
e
d
,
which are interwoven among the tracheae, fat body, muscles, and connective tissue of
the head and anterior thorax. In accord with their varied position, they have been called

p
rot
h
orac
i
c
gl
an
d
s, ventra
lh
ea
dgl
an
d
s, an
d
tentor
i
a
lgl
an
d
s, t
h
ou
gh
t
h
ese structures are

h
omo
l
o
g
ous. Exce
p
t
i
n
p
r
i
m
i
t
i
ve a
p
ter
yg
otes, so
li
tar
yl
ocusts (C
h
a
p
ter 21, Sect

i
on 7), an
d
,
apparent
l
y, wor
k
er an
d
so
ldi
er term
i
tes, t
h
eg
l
an
d
s are
f
oun
d
on
l
y
i
n
j

uven
il
e
i
nsects an
d
degenerate shortly after the molt to the adult. The molt glands show distinct cycles of activity
c
orrelated with new cuticle formation and ecdysis. Their product,
α
-
ecdysone, is a prohor-
mone that when activated initiates several im
p
ortant events in this re
g
ard (see Cha
p
ter 11
,
S
ect
i
on 3.4 an
d
C
h
a
p
ter 21, Sect

i
on
6
.1). T
ypi
ca
lly
t
h
e act
i
ve
f
orm
i
s 20-
hyd
rox
y
ec
dy
son
e
(
=
β
-
ec
d
ysone

=
ec
d
ysterone) t
h
oug
h
a
l
arge num
b
er o
f
s
i
m
il
ar mo
l
ecu
l
es w
i
t
hbi
o
l
og
i
ca

l
a
ctivity have been isolated. Ecdysones are steroids (Figure 13.6B) having the same carbon
s
keleton as cholesterol, which is almost certainly the natural precursor in insects
.
3
.4. Other Endo
c
rine Stru
c
ture
s
A
var
i
ety o
f
structures
i
n
i
nsects
h
ave
b
een propose
d
as en
d

ocr
i
ne g
l
an
d
s at one t
i
me
or another.
T
he oenoc
y
tes, which become active earl
y
in the molt c
y
cle and a
g
ain at the onset o
f
s
exua
l
matur
i
t
yi
na
d

u
l
t
f
ema
l
es, s
h
ow u
l
trastructura
l
s
i
m
il
ar
i
t
i
es w
i
t
h
stero
id
-
p
ro
d

uc
i
n
g
c
e
ll
s
i
n verte
b
rates (Loc
k
e, 19
6
9; Romer, 1991). T
hi
s
h
as
l
e
d
to t
h
esu
gg
est
i
on t

h
at t
h
ese
c
e
ll
s may
b
eas
i
te
f
or ec
d
ysone synt
h
es
i
s, an
d
a
f
ew
bi
oc
h
em
i
ca

l
stu
di
es support t
hi
s
id
ea
(Romer, 1991; Romer and Bressel, 1994). However, their primary roles appear to be the
s
ynthesis of certain cuticular lipids and the lipoprotein layer of the epicuticle (Chapter 11,
S
ection 2
)
.
In contrast to t
h
ose o
f
verte
b
rates, t
h
e
g
ona
d
so
fi
nsects

d
o not
p
ro
d
uce sex
h
ormone
s
t
h
at
i
n
fl
uence t
h
e
d
eve
l
opment o
f
secon
d
ary sexua
l
c
h
aracters. A

l
arge num
b
er o
f
exper-
iments in which insects were castrated could be cited to support this statement. The onl
y
exception to this generalization is found in the firefl
y
L
amp
y
ris nocti
l
uc
a
(
Coleoptera
)
where an andro
g
enic hormone
p
roduced b
y
the testes induces the develo
p
ment of male sex
-

ua
l
c
h
aracters. T
h
us,
i
m
pl
antat
i
on o
f
t
h
ese or
g
ans
i
nto a
f
ema
l
e
l
arva causes sex reversa
l.
O
var

i
an t
i
ssue,
h
owever,
d
oes not pro
d
uce a
h
ormone
f
or
i
n
d
uct
i
on o
ff
ema
l
eness (Na
i
sse,
1
969
).
T

he ovaries of many insects do, however, produce hormones that affect reproductiv
e
develo
p
ment. Adams and others (see Adams, 1980, 1981) have demonstrated that the ma
-
tur
i
n
g
ovar
i
es o
f
t
h
e
h
ouse
fly
,
M
u
s
ca d
o
me
s
tica,an
d

ot
h
er D
ip
tera
p
ro
d
uce an oostat
ic
h
ormone t
h
at regu
l
ates t
h
e pattern o
f
egg maturat
i
on
b
y
i
n
hibi
t
i
ng t

h
ere
l
ease o
f
OEH
f
ro
m
th
e
m
N
SC
.
In the absence of OEH, ovarian ecdysone release (see below and Chapter 19,
S
ection 3.1.1) does not occur. After oviposition, the ovaries no longer produce oostatic
4
2
1
NERV
O
U
S
AND
C
HEMI
CA
L

INTE
G
RATI
ON
h
ormone, and a new cycle of egg maturation begins. In contrast, the antigonadotropin
p
roduced b
y
the abdominal
p
eris
y
m
p
athetic neurosecretor
y
or
g
ans in the bu
g
R
h
o
d
nius
p
rolixus
d
oes not act on ot

h
er en
d
ocr
i
ne centers. Rat
h
er,
i
ta
pp
ears to act at t
h
e
l
eve
l
o
f
t
he
f
o
lli
c
l
ece
ll
s,
bl

oc
ki
ng t
h
e act
i
on o
fj
uven
il
e
h
ormone (C
h
apter 19, Sect
i
on 3.1.1) (Dave
y
and Kuster, 1981)
.
Reports of the existence of ecdysones in adult female insects, published in the 19
5
0s,
w
ere lar
g
el
y
i
g

nored (after all, the molt
g
lands that
p
roduce them were known to de
g
enerate
at t
h
een
d
o
fl
arva
l lif
e), an
di
t was not unt
il
t
h
e 1970s t
h
at t
h
eovar
y
was s
h
own to

b
ea
m
a
j
or
p
ro
d
ucer o
f
t
h
ese
h
ormones
i
n
i
nsects
f
rom a var
i
et
y
o
f
or
d
ers (e.

g
.,
l
ocusts, cr
i
c
k
ets,
t
ermites, mosquitoes and other Diptera, and several Lepidoptera). In some Diptera a clea
r
r
ole for ecdysone in vitellogenesis has been established (Chapter 19, Section 3.1.3) while in
locusts the ecd
y
sone lar
g
el
y
accumulates in maturin
g
e
gg
s to be used later in the re
g
ulation
o
f
em
b

r
y
on
i
cmo
l
t
i
n
g
(C
h
a
p
ter 20, Sect
i
on 7.2). For ot
h
er s
p
ec
i
es,
i
ts
f
unct
i
on rema
i

n
s
u
nc
l
ear
.
Ev
id
ence
f
rom a num
b
er o
f
spec
i
es
i
n
di
cates t
h
at t
h
e testes may a
l
so pro
d
uce ec

d
ys
-
t
eroids. In the moth
s
L
ymantria
d
ispar an
d
He
l
iot
h
is virescen
s
testis ecdysiotropin stim-
u
lates the testis sheaths to
p
roduce ecd
y
steroids. In turn these tri
gg
er release of testicular
f
actors t
h
at

p
romote
g
rowt
h
an
dd
eve
l
o
p
ment o
f
t
h
ere
p
ro
d
uct
i
ve tract (Loe
b
et al
.
, 199
6
)
.
E

c
dy
stero
id p
ro
d
uct
i
on
by
testes, as we
ll
as
by
t
h
ema
l
e accessor
ygl
an
d
san
d
a
bd
om
i
na
l

i
ntegument
h
as a
l
so
b
een reporte
di
not
h
er mot
h
s, cr
i
c
k
ets, an
d
grass
h
oppers (G
ill
ott an
d
Is-
m
ail, 199
5
, and references therein). However, except for a possible role in spermatogenesi

s
(
Cha
p
ter 19, Section 3.2), the function of ecd
y
steroids in these insects remains uncertain
.
An en
d
ocr
i
ne ro
l
e
f
or t
h
eIn
k
ace
ll
sw
i
t
hi
nt
h
ee
pi

trac
h
ea
lgl
an
d
s was or
igi
na
lly d
e
-
scr
ib
e
di
n
M
anduca
s
exta
(
ˇ
Z
it
ˇn
a
n
e
t al.

,
199
6
). However,
i
t
h
as recent
ly b
een confirme
d
th
at t
h
ese ce
ll
s occur
i
n representat
i
ves o
f
a
ll
ma
j
or
i
nsect or
d

ers, pro
d
uc
i
ng pre-ec
d
ys
i
s-
a
nd ecdysis-triggering hormones (PETH and ETH) at the end of each developmental stag
e
(
ˇ
Z
itˇnan
e
ta
l.
, 2003) (Chapter 21, Section 6.2). I
n
M
.sext
a
there are nine pairs of segmentally
a
rran
g
ed e
p

itracheal
g
lands, each attached to a lar
g
e trachea immediatel
y
ad
j
acent to a s
p
ir-
a
c
l
ean
d
conta
i
n
i
n
g
as
i
n
gl
eIn
k
ace
ll

. However,
i
n most
i
nsects, t
h
eIn
k
ace
ll
s are numerous
a
n
d
scattere
d
t
h
roug
h
out t
h
e trac
h
ea
l
system. Bot
h
PETH an
d

ETH are pept
id
es, t
h
e
l
atter
composed of 26 amino acids i
n
M
.sext
a
.
4. Insect Semiochemicals
I
nsects interact with other members of their species, as well as with other organisms
,
b
y means of a bewildering array of so-called semiochemicals. When the interaction is
i
ntras
p
ecific, the chemical messa
g
es are called
p
heromones. Chemicals involved in inter
-
s
p

ec
i
fic
i
nteract
i
on, a
ll
e
l
oc
h
em
i
ca
l
s,
f
a
ll i
nto two ma
j
or cate
g
or
i
es: a
ll
omones
p

rovo
k
ea
r
es
p
onse t
h
at
f
avors t
h
eem
i
tter, w
h
ereas
k
a
i
romones
i
n
d
uce a res
p
onse
f
avora
bl

etot
h
e re-
ceiver. Perhaps not surprisingly, a given semiochemical may fit into more than one of these
g
roups; for example, pheromones emitted by prey insects may also function as kairomone
s
by
attractin
gp
redators and
p
arasitoids. It should be understood that in inters
p
ecific interac-
ti
ons
i
nsects ma
yb
ee
i
t
h
er t
h
eem
i
tter or t
h

e rece
i
ver o
f
t
h
ea
ll
e
l
oc
h
em
i
ca
l
s
ig
na
l
.T
h
e
l
atte
r
i
ses
p
ec

i
a
lly i
m
p
ortant
f
or
phy
to
ph
a
g
ous
i
nsects,
f
or w
hi
c
hpl
ant-re
l
ease
d
c
h
em
i
ca

l
sma
y
b
eama
j
or
d
eterrent aga
i
nst
i
nsects attac
k
or a spec
i
fic cue
b
yw
hi
c
h
t
h
e
i
nsect recogn
i
ze
s

i
ts host (Chapter 23, Section 2.3.1). In this chapter only pheromones, and kairomones and
allomones released b
y
insects will be considered
.
422
C
HAPTER
13
4.
1
. Pheromones
P
heromones are chemicals messages produced by one individual that induce a partic
-
ular behavioral, physiological, or developmental response in other individuals of the sam
e
s
p
ecies. Like hormones, the
y
are
p
roduced in small
q
uantities; indeed, the
y
are referred to in
old

er
li
terature as “ecto
h
ormones,” a term t
h
at ma
y
ta
k
e on renewe
d
s
ig
n
i
ficance
f
o
ll
ow
i
n
g
t
h
e
di
scover
y

t
h
at
i
n term
i
tes
j
uven
il
e
h
ormone a
pp
arent
ly
serves a
l
so as a
ph
eromone t
h
at
regu
l
ates caste
diff
erent
i
at

i
on (Sect
i
on 4.1.2). P
h
eromones may
b
evo
l
at
il
ean
d
t
h
ere
f
ore ca-
p
able of being detected as an odor over considerable distances, or they may be non-volatile,
re
q
uirin
g
actual
p
h
y
sical contact amon
g

individuals for their dissemination. The
y
ma
y
b
e
highly
s
p
ec
i
fic, even to t
h
e extent t
h
at on
ly
a
p
art
i
cu
l
ar
i
somer o
f
asu
b
stance

i
n
d
uces t
he
t
ypi
ca
l
e
ff
ect
i
na
gi
ven s
p
ec
i
es. (As a coro
ll
ar
y
,c
l
ose
ly
re
l
ate

d
s
p
ec
i
es o
f
ten ut
ili
ze
diff
er
-
ent
i
somer
i
c
f
orms o
f
ag
i
ven c
h
em
i
ca
l
). P

h
eromones are re
l
ease
d
on
l
yun
d
er appropr
i
at
e
c
onditions, that is, in response to appropriate environmental stimuli, and examples of this
are given below. Thus, whereas the neural and endocrine systems coordinate the behav-
i
or,
phy
s
i
o
l
o
gy
,an
d/
or
d
eve

l
o
p
ment o
f
an
i
n
di
v
id
ua
l
,
ph
eromones re
g
u
l
ate t
h
ese
p
rocesse
s
wi
t
hi
n
p

o
p
u
l
at
i
ons.
Ph
eromones may
b
e arrange
di
n rat
h
er
b
roa
d
, somet
i
mes over
l
app
i
ng, categor
i
es
b
ase
d

o
n their functions. There are sex pheromones, caste-regulating pheromones, aggregatio
n
p
heromones, alarm pheromones, trail-marking pheromones, and spacing pheromones
.
4.
1
.
1
.
Sex Pheromones
In t
h
e term “sex
ph
eromones” are
i
nc
l
u
d
e
d
c
h
em
i
ca
l

st
h
at (1) exc
i
te an
d/
or attract
mem
b
ers o
f
t
h
e oppos
i
te sex (sex attractants), (2) act as ap
h
ro
di
s
i
acs, (3) acce
l
erate or
retard sexual maturation (in either the opposite and/or same sex), or (4) enhance fecundity
and/or reduce receptivity in the female following their transfer during copulation
.
Sex attractants are t
yp
icall

y
volatile chemicals
p
roduced b
y
either male or female mem
-
b
ers o
f
as
p
ec
i
es, w
h
ose re
l
ease an
dd
etect
i
on
by
t
h
e
p
artner are essent
i

a
lp
rere
q
u
i
s
i
tes t
o
success
f
u
l
courts
hi
pan
d
mat
i
ng. At t
h
e outset,
i
ts
h
ou
ld b
e rea
li

ze
d
t
h
at t
h
e term “sex attrac-
tant” is a misnomer; the chemical does not directly attract but initiates upwind orientation
and movement by the recipient. Male-attracting substances are produced by virgin females
o
fs
p
ecies re
p
resentin
g
man
y
insect orders, but es
p
eciall
y
Le
p
ido
p
tera and Coleo
p
tera (for
l

ists
,
see Tamaki
,
in Kerkut and Gilbert
,
1985
;
Arn et al
.
, 1992). Fema
l
es re
l
ease t
h
e
i
r
ph
eromones on
ly i
n res
p
onse to a s
p
ec
i
fic st
i

mu
l
us. Re
l
ease ma
yb
e
i
n
fl
uence
dby
a
g
e
,
repro
d
uct
i
ve status, t
i
me o
fd
ay, presence o
fh
ost p
l
ant, temperature, an
d

w
i
n
d
spee
d
.For
example, many species of moths begin “calling” (everting their pheromone-secreting glands
and exudin
g
the chemical) 1.5–2.0 hours before dawn. Other Le
p
ido
p
tera are stimulated t
o
re
l
ease
ph
eromone
by
t
h
e scent o
f
t
h
e
l

arva
lf
oo
dpl
ant
.
R
hodnius prolixus
fe
m
ales
r
elease
ph
eromone on
ly
a
f
ter a
bl
oo
d
mea
l
,an
dph
eromone
p
ro
d

uct
i
on
i
n Peri
p
laneta americana
i
s arreste
d
w
h
en t
h
e oot
h
eca
i
s
f
orme
d
. It seems t
h
at
i
n spec
i
es suc
h

as R.
p
ro
l
ixus
,
coc
k
-
roaches, locusts, and beetles, which have repeated cycles of oocyte development over a
p
eriod of time, pheromone production is under the control of the endocrine system, espe-
ci
a
lly
t
h
e cor
p
ora a
ll
ata, an
d
t
h
at t
h
ee
ff
ects o

f
st
i
mu
li
suc
h
as
f
oo
di
nta
k
eor
p
resence o
f
an oot
h
eca are me
di
ate
d
v
i
at
h
e neuroen
d
ocr

i
ne s
y
stem. In
M
u
s
ca d
o
me
s
tic
a
an
dp
er
h
a
p
s
o
t
h
er D
i
ptera, p
h
eromone synt
h
es

i
s
i
sregu
l
ate
db
yovar
i
an ec
d
ystero
id
s, w
hil
e
i
n man
y
moths PBAN (Section 3.1) mediates production of sex attractant (Tillman
e
ta
l.
, 1999;
Ryan
2002)
.
4
2
3

NERV
O
U
S
AND
C
HEMI
CA
L
INTE
G
RATI
ON
F
I
G
URE 13.7.
P
heromones. (A) Bomb
y
kol, the sex attractant of the silk moth
,
Bombyx mori
;
(B,C) hone
y
be
e
queen pheromones; (D) undecane, an alarm pheromone produced by many formicine ants; and (E) caproic acid,
a

ma
j
or com
p
onent o
f
t
h
e tra
il
-mar
ki
n
g
secret
i
on o
f
t
h
e term
i
te Zootermopsis neva
d
ensis.
T
yp
icall
y
, the

p
heromone-
p
roducin
gg
lands of female Le
p
ido
p
tera are eversible sacs
l
ocate
di
nt
h
e
i
nterse
g
menta
l
mem
b
rane
b
e
hi
n
d
t

h
ee
igh
t
h
a
bd
om
i
na
l
stem
i
te. In t
h
e
h
o-
m
o
pt
eran Schizaphis borealis
th
e
gl
an
d
s are
p
ro

b
a
bly
on t
h
e
hi
n
d
t
ibi
ae;
in
P
eriplaneta
th
ep
h
eromone seems to
b
e pro
d
uce
di
nt
h
e gut an
di
sre
l

ease
df
rom
f
eca
l
pe
ll
ets;
i
nt
he
queen honey bee the mandibular glands are the source; and in the house fly sex pheromone
i
s secreted evenly over the second through seventh abdominal segments. In Coleoptera th
e
gl
an
d
s are a
bd
om
i
na
l
.
T
h
e com
p

onents o
f
man
y
ma
l
e attractants
h
ave
b
een
id
ent
i
fie
d
,es
p
ec
i
a
lly
t
h
ose o
f
pest
if
erous Lep
id

optera
i
nw
hi
c
h
t
h
ey appear genera
ll
yto
b
ea
li
p
h
at
i
c stra
i
g
h
t-c
h
a
i
n
h
y
d

ro
-
carbons, alcohols, acetates, aldehydes, and ketones containing 10–21 carbon atoms (Figur
e
13.7A). Among Lepidoptera, species in the same family or subfamily tend to produce a
“
ke
y
com
p
onent.” For exam
p
le, (Z)-11-tetradecenol or its derivative is
p
roduced b
y
almos
t
a
ll
Tortr
i
c
i
nae. Usua
lly
t
h
esex
ph

eromone
i
sa
bl
en
d
o
f
two or more com
p
onents, occurr
i
n
g
i
ns
p
ec
i
es-s
p
ec
i
fic
p
ro
p
ort
i
ons. (Interest

i
n
gly
,t
h
e
p
ro
p
ort
i
ons ma
y
var
y
amon
gp
o
p
u
l
at
i
ons
o
f the same species in different geographic locations.) Further, only one isomeric form o
f
a component is typically attractive in a given species. As a result, under natural condition
s
m

ales res
p
ond onl
y
to the
p
heromone
p
roduced b
y
females of their s
p
ecies. Other factors
th
at serve to
p
revent
i
nters
p
ec
i
fic attract
i
on
b
etween ma
l
es an
df

ema
l
es o
f
s
p
ec
i
es
p
ro
d
uc-
i
n
g
s
i
m
il
ar
ph
eromones
i
nc
l
u
d
e
diff

erences
i
nt
h
et
i
me o
fd
a
y
at w
hi
c
h
ma
l
es are sens
i
t
i
v
e
t
op
h
eromone,
diff
erences
i
n geograp

hi
c
l
ocat
i
on o
f
t
h
e spec
i
es,
diff
erences
i
nt
h
et
i
me o
f
year when the species are sexually mature, and the need for additional stimuli, perhaps au-
d
itor
y
, visual, or chemical, before a male is attracted to a female. For exam
p
le, the “initial”
se
p

arat
i
on o
f
two s
p
ec
i
es ma
y
occur on t
h
e
b
as
i
so
f
t
h
e
i
r attract
i
on to
diff
erent
h
ost
pl

ants
.
T
h
us,
i
nt
h
ev
i
c
i
n
i
t
y
o
f
a
h
ost
pl
ant, t
h
ec
h
ances o
fb
e
i

n
g
attracte
d
to a cons
p
ec
i
fic
f
ema
le
will b
e great
l
y
i
ncrease
d
. Nevert
h
e
l
ess, ot
h
er st
i
mu
li
w

ill b
e necessary to “confirm” t
h
e
conspecific nature of the partner
.
I
n man
y
s
p
ecies (for lists, see Weatherston and Perc
y
, 1977; Tamaki, in Kerkut an
d
G
ilbert, 1985; Fitz
p
atrick and McNeil, 1988; Birch
e
tal
.
, 1990)
i
t
i
sma
l
es t
h

at
p
ro
d
uce a
sex
ph
eromone. T
hi
sma
yf
unct
i
on,
lik
et
h
ose o
ff
ema
l
es, as a
l
on
g
-
di
stance “attractant
”
o

r may tr
i
gger c
l
ose-
i
n
b
e
h
av
i
or suc
h
as s
h
ort-range attract
i
on,
f
ema
l
eor
i
entat
i
on
f
or mat-
i

ng, adoption of the mating posture, and quiescence. For example, the male cockroach,
Naup
h
oeta cinerea
,
produces seducin, which both attracts and pacifies the unmated femal
e
42
4
C
HAPTER
13
so that a connection can be established. The pheromone produced by the male boll weevil,
A
nt
h
onomus gran
d
is
,
attracts onl
y
females in summer; however, in the fall it serves as an
a
gg
re
g
at
i
on

ph
eromone, attract
i
n
gb
ot
h
ma
l
es an
df
ema
l
es. Ma
le
Tenebri
o
m
o
lit
or
p
ro
d
uc
e
b
ot
h
a

f
ema
l
e attractant an
d
an ant
i
a
ph
ro
di
s
i
ac t
h
at
i
n
hibi
ts t
h
e res
p
onse o
f
ot
h
er ma
l
es t

o
t
h
e
f
ema
l
e’s p
h
eromone. T
h
ep
h
eromone-pro
d
uc
i
ng g
l
an
d
so
f
ma
l
es are muc
h
more var
i
e

d
in their location than those of females. For example, pheromone is secreted from mandibula
r
g
lands in ants, from
g
lands in the thorax and abdomen of some beetles, from
g
lands at the
b
ase o
f
t
h
e
f
ore w
i
n
g
s
i
n some Le
pid
o
p
tera,
f
rom a
bd

om
i
na
lgl
an
d
s
i
not
h
er Le
pid
o
p
tera
an
d
coc
k
roac
h
es, an
df
rom recta
lgl
an
d
s
i
n certa

i
nD
ip
tera. As
i
n
f
ema
l
es, t
h
e attractants
p
ro
d
uce
db
yma
l
es are usua
ll
y
l
ong-c
h
a
i
na
l
co

h
o
l
sort
h
e
i
ra
ld
e
h
y
di
c
d
er
i
vat
i
ves
.
B
ecause of their specificity and effectiveness in very low concentrations, the use of sex
attractants in pest control has great potential, an aspect that will be more fully discussed i
n
Ch
a
p
ter 24, Sect
i

on 4.2.
Sexua
l
maturat
i
on-acce
l
erat
i
n
g
or -
i
n
hibi
t
i
n
gph
eromones are
p
ro
d
uce
dby
man
yi
n-
sects t
h

at ten
d
to
li
ve
i
n groups,
i
nc
l
u
di
ng soc
i
a
l
spec
i
es. T
h
ese su
b
stances serve e
i
t
h
er
to synchronize reproductive development so that both sexes mature together or, in social
species, to inhibit the reproductive capability of almost all individuals so that their energ
y

c
an be redirected to other functions. Mature male desert locusts, for exam
p
le,
p
roduce a
v
o
l
at
il
e
ph
eromone t
h
at s
p
ee
d
su
p
maturat
i
on o
fy
oun
g
er ma
l
es an

df
ema
l
es. T
h
e
ph
eromone
i
sa
bl
en
d
o
f
five components, o
f
w
hi
c
h
p
h
eny
l
aceton
i
tr
il
e appears to

b
et
h
e most cr
i
t
i
ca
l
(
Mahama
t
e
ta
l.
, 2000). Conversely, gregarious juvenile desert locusts secrete a pheromon
e
that retards the maturation of gregarious newly molted adults. This pheromone, which als
o
serves as an a
gg
re
g
ation
p
heromone for the n
y
m
p
hs, is a com

p
lex blend of chemicals, som
e
p
ro
d
uce
dby
t
h
ee
pid
erma
l
ce
ll
san
d
ot
h
ers assoc
i
ate
d
w
i
t
h
t
h

e
f
eces (Assa
d
et al.
, 199
7
).
Th
e
ph
eromones a
pp
ear to o
p
erate
by
re
g
u
l
at
i
n
g
t
h
e act
i
v

i
t
y
o
f
t
h
e cor
p
ora a
ll
ata
i
not
h
er
i
n
di
v
id
ua
l
s
.
E
ach colony of social insects has only one or very few reproducing individuals of
each sex. Most members of the colon
y
, the workers, devote their effort to maintainin

g
th
e
c
o
l
on
y
an
d
never mature sexua
lly
.T
h
e
i
r
f
a
il
ure to mature resu
l
ts
f
rom t
h
e
p
ro
d

uct
i
on
by
re
p
ro
d
uct
i
ves o
fi
n
hibi
tor
yph
eromones. In a
h
one
yb
ee co
l
on
y
t
h
e
q
ueen
p

ro
d
uces,
i
n
t
h
e man
dib
u
l
ar g
l
an
d
s, a mater
i
a
l
ca
ll
e
d
queen su
b
stance, 9-oxo-2-
d
eceno
i
cac

id
(F
i
gur
e
1
3.7B), which is spread over the body during grooming to be later licked off by attendan
t
w
orkers. Mutual feeding among workers results in the dispersal of queen substance through
the colon
y
where the
p
heromone serves to stimulate fora
g
in
g
activit
y
(in older workers)
an
d
“
h
ouse
h
o
ld d
ut

i
es” (
by y
oun
g
wor
k
ers). T
h
e
gl
an
d
sa
l
so
p
ro
d
uceavo
l
at
il
e
ph
eromone,
9
-
h
y

d
roxy-2-
d
eceno
i
cac
id
(F
i
gure 13.7C), w
hi
c
h
, toget
h
er w
i
t
h
queen su
b
stance,
i
n
hibi
t
s
o
varian development in workers. As the queen ages and/or the number of individuals in
a colony increases, the amount of pheromone available to each worker declines, and the

l
atter’s behavior chan
g
es. The workers construct
q
ueen cells in which the larvae are fed a
s
p
ec
i
a
ldi
et so t
h
at t
h
e
yd
eve
l
o
pi
nto new
q
ueens. T
h
e first new
q
ueen to emer
g

e
kill
st
h
e
o
t
h
ers an
dp
rocee
d
sonanu
p
t
i
a
l fligh
t accom
p
an
i
e
dbyd
rones. Queen su
b
stance
p
ro
d

uce
d
by the new queen now serves as a sex attractant for the drones and to stimulate them t
o
mate with her. When the new queen returns to the hive from the flight, part of the colony
swarms; that is, the old
q
ueen, accom
p
anied b
y
workers, leaves the hive to found a new
c
o
l
on
y
.A
g
a
i
n,
i
t
i
s
q
ueen su
b
stance, a

l
on
g
w
i
t
h
9-
hyd
rox
y
-2-
d
eceno
i
cac
id
,t
h
at ena
bl
e
s
w
o
r
k
ers to
l
ocate an

d
con
g
re
g
ate aroun
d
t
h
e
q
ueen. T
hi
s
i
s anot
h
er exam
pl
eo
fh
ow t
he
f
unct
i
on o
f
ap
h

eromone may vary accor
di
ng to t
h
e part
i
cu
l
ar env
i
ronmenta
l
c
i
rcumstances
in which the pheromone is released.
4
25
NERV
O
U
S
AND
C
HEMI
CA
L
INTE
G
RATI

ON
I
n the lower termites, in contrast to the honey bee, there is a pair of equally important
p
rimar
y
re
p
roductives, the kin
g
and
q
ueen. When a colon
y
is small, the develo
p
ment o
f
a
ddi
t
i
ona
l
re
p
ro
d
uct
i

ves
i
s
i
n
hibi
te
dby
means o
f
sex-s
p
ec
i
fic
ph
eromones secrete
dby
th
ero
y
a
lp
a
i
r. T
h
e
ph
eromones a

pp
arent
ly
are re
l
ease
di
nt
h
e
f
eces an
d
trans
f
erre
df
ro
m
t
erm
i
te to term
i
te
b
y trop
h
a
ll

ax
i
s. L¨usc
h
er (1972) suggeste
d
t
h
at
j
uven
il
e
h
ormone may
b
e
t
he pheromone that inhibits reproductive development, though how such an arrangemen
t
could act in a sex-s
p
ecific manner has not been satisfactoril
y
ex
p
lained. In addition, there
are
i
n

di
cat
i
ons t
h
at t
h
e
ki
n
g
secretes a
ph
eromone t
h
at en
h
ances t
h
e
d
eve
l
o
p
ment o
ff
ema
l
e

su
ppl
ementar
y
re
p
ro
d
uct
i
ves
i
nt
h
ea
b
sence o
f
t
h
e
q
ueen.
I
n some spec
i
es o
f
mosqu
i

toes an
d
ot
h
er D
i
ptera, Ort
h
optera, Hem
i
ptera, an
d
Lep
i-
d
optera, the male, during mating, transfers to the female via the seminal fluid, chemicals that
i
nhibit receptivity (willingness to mate subsequently) or enhance fecundity (by increasing
th
e rate at w
hi
c
h
e
gg
s mature an
d
are
l
a

id
)(G
ill
ott an
d
Fr
i
e
d
e
l
, 1977; G
ill
ott, 2003). In con
-
t
rast to ot
h
er
ph
eromones, t
h
esu
b
stances t
h
at are
p
ro
d

uce
di
nt
h
e accessor
y
re
p
ro
d
uct
i
v
e
gl
an
d
sort
h
e
i
r ana
l
ogue are prote
i
naceous
i
n nature. Bot
h
recept

i
v
i
ty-
i
n
hibi
t
i
ng su
b
stances
and fecundity-enhancing substances signal that insemination has occurred. The former en
-
sure that a larger number of virgin females will be inseminated; the latter, acting as they do
by
tri
gg
erin
g
ovi
p
osition, increase the
p
robabilit
y
of fertilized (viable) e
gg
s bein
g

laid (i
n
m
ost s
p
ec
i
es un
f
ert
ili
ze
d
e
gg
s are
i
nv
i
a
bl
e). Bot
h
t
yp
es o
fph
eromones serve, t
h
ere

f
ore, to
i
ncrease t
h
e repro
d
uct
i
ve economy o
f
t
h
e spec
i
es
.
4.1.2. Caste-Regulating Pheromones
As note
di
nt
h
e
p
rev
i
ous sect
i
on,
i

n soc
i
a
li
nsects ver
yf
ew mem
b
ers o
f
aco
l
on
y
ever
m
ature sexua
ll
y, t
h
e
i
r repro
d
uct
i
ve
d
eve
l

opment
b
e
i
ng
i
n
hibi
te
db
yp
h
eromones so t
h
at t
h
ese
i
ndividuals (forming the worker caste) can perform other activities for the benefit of th
e
colony as a whole. In addition to the worker caste, there exists in termites and ants a soldier
caste. The number of soldiers
p
resent is
p
ro
p
ortional to the size of the colon
y
, a featur

e
su
gg
est
i
n
g
t
h
at so
ldi
ers re
g
u
l
ate t
h
e num
b
ers
i
nt
h
e
i
r ran
k
s
by p
ro

d
uct
i
on o
f
aso
ldi
er-
i
n
hibi
t
i
ng p
h
eromone. However, t
h
es
i
tuat
i
on
i
sma
d
e more comp
li
cate
db
y a pos

i
t
i
ve
i
nfluence on soldier production (presumably pheromonal) on the part of the reproductives.
The regulation of caste differentiation in social insects is a morphogenetic phenomenon,
j
ust as are the chan
g
es from larva to larva, larva to
p
u
p
a, and
p
u
p
a to adult. Such chan
g
es
d
e
p
en
d
on t
h
e act
i

v
i
t
y
o
f
t
h
e cor
p
ora a
ll
ata (
l
eve
l
o
fj
uven
il
e
h
ormone
i
nt
h
e
h
emo
ly

m
ph
)
f
or t
h
e
i
r man
if
estat
i
on. It
i
s not sur
p
r
i
s
i
n
g
,t
h
ere
f
ore, t
h
at t
h

e
ph
eromones re
g
u
l
at
i
n
g
cast
e
diff
erent
i
at
i
on (
i
nc
l
u
di
ng t
h
e
d
eve
l
opment o

f
repro
d
uct
i
ves) exert t
h
e
i
re
ff
ect, u
l
t
i
mate
l
y, v
ia
t
he corpora allata (Chapter 21, Section 7). In lower termites, for example, soldier formation
can be induced in ex
p
erimental colonies b
y
administration of
j
uvenile hormone (throu
g
h

f
ee
di
n
g
,to
pi
ca
l
a
ppli
cat
i
on, or as va
p
or). T
h
us, t
h
eso
ldi
er-
i
n
hibi
t
i
n
gph
eromone ma

y
ac
t
by i
n
hibi
t
i
n
g
t
h
e cor
p
ora a
ll
ata or
by
com
p
et
i
n
g
w
i
t
hj
uven
il

e
h
ormone at
i
ts s
i
te o
f
act
i
o
n
(
L¨usc
h
er, 1972)
.
4.1.3. Aggregation Pheromones
A
gg
re
g
at
i
on
ph
eromones are
p
ro
d

uce
dby
e
i
t
h
er one or
b
ot
h
sexes an
d
serve to attrac
t
o
ther individuals for feeding, mating, and/or protection. They occur in Collembola, Diptera
,
Hemiptera, Orthoptera, and Dictyoptera, but are especially well known in Coleoptera, par-
t
icularl
y
the bark and ambrosia beetles (Scol
y
tinae). Larvae of the crane fl
y
Tipu
l
a simp
l
ex

42
6
C
HAPTER
13
release a pheromone in their feces that causes aggregation under cowpats and rotting woo
d
w
here food and shelter occur. Likewise, Collembola a
gg
re
g
ate in moist
p
laces in res
p
ons
e
to a
ph
eromone to avo
id d
es
i
ccat
i
on an
d
to re
p

ro
d
uce; t
h
e
l
atter
i
ses
p
ec
i
a
lly
s
ig
n
i
ficant as
t
h
ese art
h
ro
p
o
d
s
d
o not co

p
u
l
ate (C
h
a
p
ter 19, Sect
i
on 4.1). In Co
l
eo
p
tera t
h
e
ph
eromones
serve pr
i
mar
il
y to aggregate t
h
e
b
eet
l
es to a
f

oo
d
source t
h
at may
b
e
i
so
l
ate
d
(e.g., store
d
grain) or require the collaborative efforts of a large number of insects to overcome host
resistance (e.
g
., bark beetles attackin
g
health
y
trees). As noted in Section 4.1.1,
j
uvenil
e
l
ocusts
p
ro
d

uce an a
gg
re
g
at
i
on
ph
eromone w
h
ose
f
unct
i
on
i
sto
k
ee
p
t
h
e marc
hi
n
g
swar
m
i
ntact. However,

g
re
g
ar
i
ous a
d
u
l
t
f
ema
l
es a
l
so
p
ro
d
uceavo
l
at
il
ea
gg
re
g
at
i
on

ph
eromone
in
t
h
e
i
r egg po
df
rot
h
(Sa
i
n
i
e
ta
l
.
,
199
5
). The pheromone, whose most important component
s
are acetophenone and veratrole (Ra
i
e
ta
l.
, 1997), attracts egg-laying females to a commo

n
site, resulting in very high egg-pod densities. In addition, it predisposes the hatchlings to
ta
k
eon
g
re
g
ar
i
ous c
h
aracter
i
st
i
cs o
f
co
l
or,
phy
s
i
o
l
o
gy
,an
db

e
h
av
i
or
.
A
gg
re
g
at
i
on
ph
eromones are a
l
so common
i
naw
id
e ran
g
eo
fbl
oo
d
-
f
ee
di

n
gi
nsects
,
serv
i
ng to
b
r
i
ng conspec
i
fics toget
h
er
f
or mat
i
ng, ov
i
pos
i
t
i
on, an
dl
arv
i
pos
i

t
i
on (McCa
ll
,
2
002). For these specialized insects, the pheromones facilitate the concentration of popu-
l
ations in sites where mating and egg-laying can occur in relative safety (e.g., cracks an
d
c
revices in walls for bedbu
g
s), or in locations where conditions are suitable for e
gg
-la
y
in
g
.
F
o
re
xam
pl
e, t
h
ee
gg
so

f
C
ulex
m
os
q
u
i
toes
,
S
imulium
(bl
ac
kfli
es), an
d
san
dfli
es re
l
eas
e
ap
h
eromone t
h
at tr
i
ggers mass ov

i
pos
i
t
i
on. L
ik
ew
i
se, tsetse
fli
es
l
arv
i
pos
i
t
i
n
l
arge ag
-
gregations, especially in the dry season when suitable sites may be rare, as a result of
a
p
heromone released as an anal exudate by the burrowing larva.
Com
p
ared to sex

p
heromones, relativel
y
little work has been done to establish the
ch
em
i
ca
l
nature o
f
a
gg
re
g
at
i
on
ph
eromones. T
h
ose stu
di
e
d
most
ly
a
pp
ear to

b
em
i
xture
s
of
com
p
oun
d
s, o
f
ten
i
nc
l
u
di
n
g
ter
p
eno
id
com
p
oun
d
san
d

c
y
c
li
ca
l
co
h
o
l
sora
ld
e
hyd
es, t
h
a
t
act synerg
i
st
i
ca
ll
y. G
i
ven t
h
e
i

r
f
unct
i
on,
i
t
i
s not surpr
i
s
i
ng to
di
scover t
h
at t
h
e aggregat
i
o
n
p
heromones of many beetles are metabolites of inhaled or ingested host-plant substances
and that host odors s
y
ner
g
ize their effect (Borden, in Kerkut and Gilbert, 1985). Like sex
ph

eromones, a
gg
re
g
at
i
on
ph
eromones are t
ypi
ca
lly highly
s
p
ec
i
fic,
p
art
i
cu
l
ar stereo an
d
op
t
i
ca
li
somers

b
e
i
n
g
attract
i
ve to a
gi
ven s
p
ec
i
es. Beet
l
ea
gg
re
g
at
i
on
ph
eromones ar
e
rare
l
y pro
d
uce

db
y exocr
i
ne g
l
an
d
s. Common
l
yt
h
ey are re
l
ease
di
nt
h
e
f
eces t
h
oug
h
t
he
p
recise sites of synthesis remain unclear. Pheromones produced from ingested material
c
ould be produced by cells in the gut wall or, as has been suggested for a few species, by
g

ut microor
g
anisms; those derived from host-
p
lant va
p
ors taken u
p
via the tracheal s
y
ste
m
are
p
er
h
a
p
ss
y
nt
h
es
i
ze
di
nt
h
e
h

emo
ly
m
ph
(
f
at
b
o
dy
?) or Ma
lpighi
an tu
b
u
l
es. It
h
as
b
een
suggeste
d
t
h
at some p
h
eromones arose
i
n

i
t
i
a
ll
yas
d
etox
i
ficat
i
on pro
d
ucts, t
h
e
i
r precursors
being toxic to the beetles so that their modern function of promoting aggregation develope
d
secondarily (Borden, 1982).
4
.
1
.4. Alarm Pheromones
As their name indicates, alarm pheromones warn members of a species of impendin
g
dan
g
er. The

y
are
p
roduced b
y
mites and insects that live in
g
rou
p
s, includin
g
social forms,
f
or exam
pl
e, coc
k
roac
h
es, tree
h
o
pp
ers, a
phid
s,
b
e
db
u

g
s, term
i
tes, an
d
soc
i
a
l
H
y
meno
p
tera
(Blum, in Kerkut and Gilbert, 198
5
; Blum, 1996). In termites it is onl
y
soldiers that
p
roduce
(an
d
respon
d
to) t
h
ep
h
eromone. Among Hymenoptera,

h
ornets an
dh
oney
b
ees,
b
ut not
b
u
mble bees, produce alarm pheromones as do almost all ants investigated. The pheromone
s
ma
y
ori
g
inate internall
y
, bein
g
released as in treeho
pp
ers when the bod
y
wall is broke
n
4
27
NERV
O

U
S
AND
C
HEMI
CA
L
INTE
G
RATI
ON
open, or in exocrine glands. Corpses (but not, living specimens) of P.
a
mericana release
m
aterial that re
p
els cons
p
ecifics and members of some other s
p
ecies. Thus, the re
p
ellent
m
a
yb
e a cue t
h
at coc

k
roac
h
es use to avo
id
areas w
h
ere ot
h
ers
h
ave
di
e
d
(Ro
ll
o
e
t al.
,
199
5
). Some H
y
meno
p
tera have more than one
p
heromone-

p
roducin
gg
land; for exam
p
le,
in
Fo
rm
i
c
a
spec
i
es o
f
ants t
h
ere are man
dib
u
l
ar g
l
an
d
s, Du
f
our’s g
l

an
d
s, an
d
po
i
son g
l
an
d
s
.
The chemical nature of alarm pheromones is highly varied but tends to be specific for
e
ach
g
rou
p
. Mites, a
p
hids, and termite soldiers
p
roduce ter
p
enoid com
p
ounds, while hone
y
b
ees

p
ro
d
uceam
i
xture o
f
acetates, an a
l
co
h
o
l
,an
d
a
k
etone. Form
i
c
i
ne ants a
l
so
p
ro
d
uce
t
er

p
eno
id
s suc
h
as c
i
tra
l
an
d
c
i
trone
ll
a
l
an
d
,
i
na
ddi
t
i
on,
f
orm
i
cac

id
,un
d
ecane (F
ig
ure
13.7D), an
d
var
i
ous
k
etones. T
h
ese compoun
d
so
f
ten act synerg
i
st
i
ca
ll
y. Typ
i
ca
ll
y, t
h

ea
l
arm
pheromones of non-social insects and mites stimulate dispersal (escape behavior). Such
b
ehavior is also seen in social species away from the nest. However, when the pheromone
i
sre
l
ease
d
near t
h
e nest, t
h
e
i
nsects are attracte
d
towar
d
t
h
e source an
d
ma
y
su
b
se

q
uent
ly
attac
k
t
h
e
i
ntru
d
er. In
h
one
yb
ees,
f
or exam
pl
e, t
h
e
ph
eromone
i
sre
l
ease
df
rom t

h
est
i
n
g
s
h
a
f
t (em
b
e
dd
e
di
nt
h
e
i
ntru
d
er!) caus
i
ng more
b
ees to attac
k.
Alarm pheromones frequently have other additional functions especially as allomones,
leading H¨olldobler (1984) to speculate that they evolved originally as defensive chemicals.
Those of ants, for exam

p
le, ma
y
also serve as defensive com
p
ounds, re
p
ellin
g
intruders, or
r
e
l
ease
diggi
n
gb
e
h
av
i
or (
p
er
h
a
p
sana
d
a

p
tat
i
on
f
or excavat
i
n
g
ants
b
ur
i
e
di
nacave-
i
n), o
r
act as tra
il
p
h
eromones. In t
h
e
h
oney
b
ee t

h
ea
l
arm p
h
eromone may
b
ere
l
ease
d
to
i
n
di
cat
e
a depleted food source
.
4.1.5. Trail-Marking Pheromone
s
Tra
il
-mar
ki
ng p
h
eromones are use
db
y some

i
nsects to fin
d
mates, to commun
i
cate
i
nformation on the location and quantity of food (and thus to recruit nest mates for foo
d
collection), and to ensure that a migrating group retains its integrity. The trails may b
e
t
errestrial, laid out on a solid substrate, or aerial, bein
g
released b
y
a stationar
y
insect and
d
e
p
en
d
ent on movement o
f
t
h
e surroun
di

n
g
me
di
um to
g
enerate a tra
il
(
i
nt
hi
s sense, t
h
en,
th
esexan
d
aggregat
i
on p
h
eromones
di
scusse
d
ear
li
er cou
ld

equa
ll
y
b
e cons
id
ere
d
as tra
il-
m
arking pheromones). Terrestrial trail-marking pheromones, which are laid as a solid line
o
r as a series of spots, are produced from a variety of glands.
Trail-markin
gp
heromones are es
p
eciall
y
well studied in social insects. In termite
s
th
e sterna
lgl
an
d
secretes t
h
e

ph
eromone as t
h
ea
bd
omen
i
s
d
ra
gg
e
d
a
l
on
g
or
p
er
i
o
di
ca
lly
p
resse
d
to t
h

esu
b
strate. In ants tra
il
-mar
ki
n
gph
eromones ma
yb
e
p
ro
d
uce
di
nt
h
e
hi
n
dg
ut
,
Du
f
our’s g
l
an
d

,po
i
son g
l
an
d
, ventra
l
g
l
an
d
s, or on t
h
e metat
h
orac
i
c
l
egs, an
d
are re
l
ease
d
as the abdomen or limbs make contact with the substrate. Ant trail-marking pheromone
s
are secreted as fora
g

in
g
workers return to the nest and serve to recruit other workers to
a
f
oo
d
source. However, t
h
e
y
ma
yb
ea
l
so use
d
to
di
rect ot
h
er
i
n
di
v
id
ua
l
stos

i
tes w
h
er
e
n
est re
p
a
i
rs are necessar
y
or
d
ur
i
n
g
swarm
i
n
g
. Most tra
il
s are re
l
at
i
ve
ly

s
h
ort-
li
ve
d
an
d
f
a
d
ew
i
t
hi
n a matter o
f
m
i
nutes un
l
ess cont
i
nuous
l
yre
i
n
f
orce

d
. Some ants,
h
owever, ma
k
e
t
rails that last for several days. Furthermore, when a source of food is good, more returning
w
orkers secrete
p
heromone, thereb
y
establishin
g
a stron
g
trail to which more workers will
b
e attracte
d
.T
h
e
ph
eromone-
p
ro
d
uc

i
n
ggl
an
d
so
f
t
h
e
h
one
yb
ee wor
k
er are
di
str
ib
ute
d
over
th
e
b
o
dy
an
d
t

h
e
ph
eromone
i
s trans
f
erre
dd
ur
i
n
gg
room
i
n
g
to t
h
e
f
eet. It
i
st
h
ere
by d
e
p
os

i
te
d
at t
h
e open
i
ng to t
h
e
hi
ve w
h
ere
i
t
b
ot
h
attracts return
i
ng wor
k
ers an
d
st
i
mu
l
ates t

h
em to
e
nter. The cavity-inhabiting wasps Ves
p
a crabr
o
an
d
V
espu
l
avu
lg
ari
s
lay a pheromone
t
rail between the cavity entrance and the entrance to their nest. The pheromone, which is
42
8
C
HAPTER
13
identical to the cuticular hydrocarbons, enables returning foragers to locate the nest unde
r
the low li
g
ht conditions of the cavit
y

(Steinmetz
e
ta
l
.
, 2002
,
2003)
.
Amon
g
non-soc
i
a
li
nsects, tra
il
-mar
ki
n
gph
eromones are we
ll k
nown
i
n coc
k
-
roac
h

es an
dg
re
g
ar
i
ous cater
pill
ars. For exam
pl
e, t
h
e tra
il
-mar
ki
n
gph
eromone o
f
P.
am
e
r
i
can
a
serves to aggregate
b
ot

h
a
d
u
l
ts an
dj
uven
il
es. Among Lep
id
optera, tra
il-
marking pheromones are released by gregarious caterpillars in diverse families, for example
,
the forest tent cater
p
illar (Ma
l
acosoma
d
isstri
a
) (Lasiocam
p
idae), the
p
ine
p
rocessionar

y
c
ater
pill
ar
(
T
haumetopoea pit
y
ocampa
)(
Noto
d
ont
id
ae
)
,an
d
Hy
lesia lineata
(
Saturn
iid
ae
)
(F
i
tz
g

era
ld
, 2003). Tra
il ph
eromones are a
l
so
p
ro
d
uce
dby
t
h
e
g
re
g
ar
i
ous
l
arvae o
f
t
h
ere
d-
headed pine sawfly (
Neodiprion lecontei

((
)(F
l
owers an
d
Costa, 2003). In t
h
ese examp
l
es
,
the trail pheromones are used to recruit conspecifics to a feeding site, to enable foragers
to return to the colony, and to maintain colony integrity, especially when the colony as a
wh
o
l
emovestoanew
l
ocat
i
on
.
K
now
l
e
dg
eo
f
t

h
ec
h
em
i
str
y
o
f
tra
il
-mar
ki
n
gph
eromones
i
sa
l
most ent
i
re
ly
confine
d
to t
h
ose o
f
soc

i
a
li
nsects. In term
i
tes an
d
many ants t
h
ey appear to
b
em
i
xtures o
fl
ong-c
h
a
in
f
atty acids, alcohols, aldehydes, esters, or hydrocarbons (Figure 13.7E). However, within
f
f
these mixtures one or two compounds are typically the major component. For example
,
o
f the 10 com
p
onents identified in the trail
p

heromone of the an
t
M
a
y
riella overbecki
o
n
ly
one, met
hyl 6
-met
hyl
sa
li
c
yl
ate e
li
c
i
te
d
tra
il f
o
ll
ow
i
n

g
(Ko
hl
et al
.
, 2000). Var
yi
n
g
d
egrees o
f
spec
i
es spec
i
fic
i
ty are o
b
serve
d
. For examp
l
e, spec
i
es o
f
S
oleno

p
sis (
fi
re ants
)
have a common pheromone, and among leafcutting ants (
A
tt
a
(
(
spp.), species will follow the
trails of congenerics. In contrast, the Argentine ant, Iri
d
om
y
rmex
h
umi
l
is, follows a trail of
(Z)-9-hexadecenal but not of its
g
eometric isomer, (E)-9-hexadecenal.
4
.1.6. S
p
acin
g(
E

p
ideictic
)
Pheromones
A relatively new discovery in pheromone research are those pheromones that stimulat
e
i
nsects to s
p
rea
d
out so as to ma
i
nta
i
nano
p
t
i
ma
lp
o
p
u
l
at
i
on
d
ens

i
t
y
.T
h
e
y
ma
yb
e
p
ro
d
uce
d
by i
mmature an
d
a
d
u
l
t
i
nsects an
d
ma
yb
eo
lf

actor
y
or tact
il
e. S
p
ac
i
n
gph
eromones
h
ave
b
een
b
est stu
di
e
di
nre
l
at
i
on to ov
i
pos
i
t
i

on. For examp
l
e, a
f
ter
l
ay
i
ng, t
h
e
f
ema
l
e app
l
e
maggot fly
,
Rh
a
g
o
l
etis pomone
ll
a, releases a pheromone that deters oviposition on the frui
t
by other females (Prokopy, 1981). The pheromone appears to be released from the hindgu
t

as the ovi
p
ositor is dra
gg
ed over the fruit. It a
pp
ears to be a water-soluble
p
e
p
tide that
rema
i
ns
bi
o
l
o
gi
ca
lly
act
i
ve
f
or severa
ld
a
y
sa

f
ter
d
e
p
os
i
t
i
on
.
Severa
l
Le
pid
o
p
tera a
l
so
p
ro
d
uce ov
ip
os
i
t
i
on-

d
eterr
i
n
gph
eromones t
h
at
li
m
i
tt
h
e num-
ber of eggs laid on a given plant (Schoonhoven, 1990); further, the presence of feeding larva
e
o
f Pieris brassicae inhibits egg laying, suggesting that the larvae also produce a pheromone
.
In the case of the flour moth,
A
nagasta
k
uhniella
¨
,
meetin
g
s between larvae result in th
e

re
l
ease o
fph
eromone
f
rom t
h
e
i
r man
dib
u
l
ar
gl
an
d
s. A
b
ove a certa
i
n
l
eve
l
o
fph
eromone,
re

fl
ect
i
n
g
t
h
e num
b
er o
f
encounters an
dh
ence t
h
e
d
ens
i
t
y
o
fl
arvae
i
nt
h
eme
di
um, a

d
u
lt
f
ema
l
es w
ill
not ov
i
pos
i
t. However, ov
i
pos
i
t
i
on
i
sst
i
mu
l
ate
d
at
l
ow p
h

eromone con
-
c
entrations which are indicative of a medium suitable for larval development but no
t
o
vercrowded
.
As note
di
n Sect
i
on 4.1.3,
b
ar
kb
eet
l
es
p
ro
d
uce an a
gg
re
g
at
i
on
ph

eromone to ensure
a
“co
ll
ect
i
ve e
ff
ort” w
h
en
i
n
i
t
i
a
lly
attac
ki
n
g
new
h
ost trees. However, res
id
ent
f
ema
l

es su
b
se-
q
uent
l
yre
l
ease a spac
i
ng p
h
eromone (ver
b
enone) w
h
ose
f
unct
i
on
i
store
d
uce conspec
i
fic
c
ompetition for egg-laying sites so that the output of each female is not compromise
d

(
Borden, 1982
).
4
2
9
NERV
O
U
S
AND
C
HEMI
CA
L
INTE
G
RATI
ON
4
.2. Ka
i
romones
O
lfaction is the major sense by which insects search for and locate their host, whether it
i
s a plant or another animal. The host’s odor, or less commonly its taste, is therefore serving
as a kairomone for the searchin
g
insect (Cha

p
ter 23, Sections 3.3.1 and 4.2.2). Insects tha
t
p
re
y
on or
p
aras
i
t
i
ze ot
h
er
i
nsects are es
p
ec
i
a
lly
a
d
e
p
tat
l
ocat
i

n
g
t
h
e
i
r
h
ost us
i
n
g
c
h
em
i
ca
l
cues. T
h
ese cues ma
yi
nc
l
u
d
et
h
eo
d

or o
f
t
h
e
p
re
yi
nsect’s
h
ost
pl
ant, t
h
eo
d
or or taste o
f
th
e prey
i
tse
lf
,an
d
p
h
eromones or, rare
l
y, a

ll
omones re
l
ease
db
yt
h
e prey
d
ur
i
ng t
h
e course
of other activities.
Pheromones, in
p
articular, have been ex
p
loited b
yp
redators and
p
arasites in order to
l
ocate t
h
e
i
r

h
ost, as t
h
e
f
o
ll
ow
i
n
g
exam
pl
es
ill
ustrate. T
h
eov
ip
os
i
t
i
on-
d
eterr
i
n
gph
eromone

pl
ace
d
on
f
ru
i
t
by
t
h
ea
ppl
ema
gg
ot
fly
(Sect
i
on 4.1.
6
)a
ll
ows t
h
e
b
racon
id p
aras

i
to
id
Op
ius lectu
s
to
l
ocate
i
ts
h
ost’s eggs. L
ik
ew
i
se, t
h
e spac
i
ng p
h
eromone re
l
ease
db
y
l
arvae
o

f
A
na
g
asta
k
uhniella
¨
e
nables their predator, the ichneumonid
N
emer
i
t
i
s canescens,t
o
d
etermine their position. Aggregation pheromones are widely used by predators for prey
-
fin
di
n
g
.T
h
us, c
l
er
id

an
d
tro
g
os
i
t
iid b
eet
l
es are stron
gly
attracte
d
to trees un
d
er ear
ly
attac
k
by b
ar
kb
eet
l
es as a resu
l
to
f
t

h
ea
gg
re
g
at
i
on
ph
eromone t
h
at t
h
e
l
atter em
i
t (Ha
y
nes an
d
Birch, in Kerkut and Gilbert, 198
5
). Predators or egg parasitoids often “eavesdrop” on the
sex attractants released by female Lepidoptera: the predators locate and feed on the adul
t
m
oths, while the parasitoids “hang around” until the moth lays its eggs soon after mating
(S
tow

e
et al.
,
1995; Boo and Yan
g
, 2000).
T
h
e
ph
eromones o
f
soc
i
a
li
nsects are ex
pl
o
i
te
di
nvar
i
ous wa
y
s
by p
re
d

aceous an
d
p
aras
i
t
i
c
i
nsects, as we
ll
as
by
ot
h
er soc
i
a
l
s
p
ec
i
es,
f
or exam
pl
e, s
l
ave-ma

ki
n
g
ants. Some
b
eetle predators, having located a pheromone trail, simply ambush passing foragers or ro
b
t
hem of their food. Many “guests” of ant nests, including species of beetles, flies, and
Th
y
sanura, find their wa
y
to the host colon
y
usin
g
the ants’ trail
p
heromones. (Further
,
some “
g
uests”
p
ro
d
uce cut
i
cu

l
ar
hyd
rocar
b
ons
id
ent
i
ca
l
to t
h
ose o
f
t
h
e
i
r
h
osts, ena
bli
n
g
th
emse
l
ves to rema
i

n unreco
g
n
i
ze
d
w
hil
et
h
e
yf
ee
d
on, or are
f
e
dby
,t
h
e ants!
)
Remar
k
a
bl
y,
i
n rare
i

nstances, a
ll
omones re
l
ease
db
yt
h
e
h
ost as a means o
fd
e
f
en
di
ng
i
tself are used by some predators and parasites to locate the emitter. Thus, a number of aphid
s
p
ecies emit (
E
)-
β
-farnesene as a defensive com
p
ound from their cornicles. However, th
e
com

p
oun
di
s use
dby
searc
hi
n
g
seven-s
p
ot
l
a
dybi
r
db
eet
l
es,
C
occinella septempunctat
a
,
as
an a
phid
-
l
ocat

i
n
g
cue (A
l
A
b
ass
i
e
t al.
,
2000)
.
4
.
3
. Allomone
s
I
nsects release a wide array of volatile chemicals that affect the behavior of other
animals, both vertebrate and invertebrate
(
Blum 1981; Whitman
e
ta
l.
, 1990). The great
m
a

j
orit
y
of these secretions are used as defensive allomones; however, a few exam
p
les o
f
a
ll
omones use
d
a
gg
ress
i
ve
ly h
ave
b
een
di
scovere
d
(B
l
um, 199
6
). T
h
ec

h
em
i
ca
l
nature o
f
a
ll
omones
i
s extreme
l
yvar
i
e
d
(see B
l
um, 1981). However,
i
t
h
as
l
ong
b
een recogn
i
ze

d
t
hat some allomones are chemically very similar, even identical, to alarm pheromones an
d
sex attractants, leading to the proposal that the original role for these compounds was
d
efensive, with the
p
heromonal function arisin
g
secondaril
y
(Blum, 1996; R
y
an, 2002)
.
T
h
ea
ll
omones are t
ypi
ca
lly p
ro
d
uce
di
ns
p

ec
i
fic exocr
i
ne
gl
an
d
s, t
h
ou
gh i
na
f
ew s
p
ec
i
e
s
th
ea
ll
omone
i
sse
q
uestere
d
w

i
t
hi
nt
h
e
h
emo
ly
m
ph
,to
b
ere
l
ease
d
as a resu
l
to
f
“re
fl
ex
b
leeding,” that is, when hemolymph is exuded at joints and intersegmental membranes. Th
e
b
iosynthetic pathways are, for most allomones, not well understood, but it is evident tha
t