II
A
natom
y
and Ph
y
siolo
gy
11
The Inte
g
umen
t
1
. Intr
oduc
t
ion
The integument of insects (and other arthropods) comprises the basal lamina, epidermis
,
and cuticle. It is often thou
g
ht of as the “skin” of an insect but it has man
y
other functions
(
Loc
k
e, 1974). Not on
ly d
oes

i
t
p
rov
id
e
phy
s
i
ca
lp
rotect
i
on
f
or
i
nterna
l
or
g
ans
b
ut,
b
ecaus
e
o
fi
ts r

igidi
t
y
,
i
t serves as a s
k
e
l
eton to w
hi
c
h
musc
l
es can
b
e attac
h
e
d
.Ita
l
so re
d
uces wate
r
loss to a very low level in most Insecta, a feature that has been of great significance in the
ev
olution of this predominantly terrestrial class. In addition to these primary functions, the

cuticular com
p
onent of the inte
g
ument
p
erforms a number of secondar
y
duties. It acts as
a meta
b
o
li
c reserve, to
b
e use
d
c
y
c
li
ca
lly
to construct t
h
e next sta
g
e, or
d
ur

i
n
gp
er
i
o
d
so
f
g
reat meta
b
o
li
c act
i
v
i
t
y
or starvat
i
on. It
p
revents entr
y
o
ff
ore
ig

n mater
i
a
l
,
b
ot
hli
v
i
n
g
an
d
n
on
li
v
i
ng,
i
nto an
i
nsect. In many
i
nsects t
h
e waxy outer
l
ayer serves as a repos

i
tory
f
or
contact sex pheromones (Chapter 13, Section 4.1.1). The color of insects is also a function
of the inte
g
ument, es
p
eciall
y
the cuticular com
p
onent
.
T
h
e
i
nte
g
ument
i
snotaun
if
orm structure. On t
h
e contrar
y
,

b
ot
hi
ts ce
ll
u
l
ar an
d
ace
ll
u
l
ar
com
p
onents ma
yb
e
diff
erent
i
ate
di
navar
i
et
y
o
f

wa
y
stosu
i
tan
i
nsect’s nee
d
s. E
pid
erma
l
ce
ll
s may
f
orm spec
i
a
li
ze
d
g
l
an
d
st
h
at pro
d

uce components o
f
t
h
e cut
i
c
l
e or may
d
eve
l
op
i
nto particular parts of sense organs. The cuticle itself is variously differentiated accordin
g
t
o the function it is re
q
uired to
p
erform. Where muscles are attached or where abrasion
m
a
y
occur
i
t
i
st

hi
c
k
an
d
r
igid
;at
p
o
i
nts o
f
art
i
cu
l
at
i
on
i
t
i
s
fl
ex
ibl
ean
d
e

l
ast
i
c; over some
sensor
y
structures
i
tma
yb
e extreme
ly
t
hi
n.
2.
S
tructur
e
The innermost component of the integument (Figure 11.1) is the basal lamina, an
amorphous but selectively porous acellular layer that is attached by hemidesmosomes to
t
he e
p
idermal cells. It is u
p
to 0.5
µ
m thick and is produced mainly by the epidermis, though
µ

µ
th
ere are re
p
orts t
h
at
h
emoc
y
tes a
l
so
p
art
i
c
ip
ate. T
h
ec
h
em
i
ca
l
nature o
f
t
h

e
b
asa
ll
am
i
na
i
s
p
oor
ly
un
d
erstoo
d
t
h
ou
gh
neutra
l
muco
p
o
ly
sacc
h
ar
id

e,
gly
co
p
rote
i
ns, an
d
co
ll
a
g
en, s
i
m
il
a
r
t
o that of vertebrates, have been identified.
The epidermis (hypodermis) is a more or less continuous sheet of tissue, one cel
l
t
hick, res
p
onsible for secretin
g
the bulk of the cuticle. Durin
gp
eriods of inactivit

y
, its
3
5
5
356
CHAPTER
11
F
I
GU
RE 11.1
.
D
iagrammatic cross-section of mature integument
.
c
ells are flattened and intercellular boundaries are indistinct. When active, the cells are
more or
l
ess cu
b
o
id
a
l
,an
d
t
h

e
i
r
pl
asma mem
b
ranes are rea
dily
a
pp
arent; one to severa
l
nuc
l
eo
li
, extens
i
ve rou
gh
en
d
o
pl
asm
i
c ret
i
cu
l

um, an
d
man
y
Go
lgi
com
pl
exes are ev
i
-
d
ent (Loc
k
e, 1991, 1998). A c
h
aracter
i
st
i
c
f
eature o
f
t
h
eap
i
ca
l

(cut
i
c
l
e-
f
ac
i
ng) sur
f
ace
o
f epidermal cells are the plasma membrane plaques, specialized regions of the plasm
a
membrane at the tips of fingerlike microvilli, from which the cuticulin envelope and new
chi
t
i
nfi
b
ers ar
i
se (Sect
i
on 3.1). E
l
ectron m
i
crosco
py h

as s
h
own t
h
at, at metamor
ph
os
i
s,
t
h
ee
pid
erma
l
ce
ll
s
d
eve
l
o
pb
asa
lp
rocesses (“
f
eet”) w
hi
c

h
can exten
d
to
b
ecome con-
necte
d
w
i
t
h
t
h
e
b
asa
ll
am
i
na an
d
w
i
t
h
ot
h
er ep
id

erma
l
ce
ll
s. W
h
en t
h
e
f
eet s
h
orten, t
h
e
basal lamina is buckled and rearrangement of cells occurs, resulting in a change in the
insect’s shape, for example, from a long, thin caterpillar to a short, fat pupa (Locke, 1991
,
1
998). E
p
idermal cells also
p
ossess the abilit
y
to develo
p
various forms of c
y
toskele-

ta
l
extens
i
ons w
hi
c
h
can
b
e use
d
,
f
or exam
pl
e, to
d
raw trac
h
eo
l
es c
l
oser to t
h
ece
ll f
or
i

ncrease
d
ox
yg
en su
pply
,ortoma
i
nta
i
n
i
nterce
ll
u
l
ar contact as t
h
ece
ll
sm
ig
rate
d
ur-
ing wound healing and changes in body shape. The density of cells in a particular are
a
v
aries, following a sequence that can be correlated with the molting cycle. The cells ofte
n

c
ontain
g
ranules of a reddish-brown
p
i
g
ment, insectorubin, which in some insects con-
tr
ib
utes s
ig
n
i
ficant
ly
to t
h
e
i
rco
l
or. However,
i
n most
i
nsects co
l
or
i

s
p
ro
d
uce
dby
t
h
e cut
i
c
l
e
(Sect
i
on 4.3).
E
p
id
erma
l
ce
ll
s may
b
e
diff
erent
i
ate

di
nto sense organs or spec
i
a
li
ze
d
g
l
an
d
u
l
ar ce
ll
s
.
O
enocytes are large, ductless, often polyploid cells, up to 10
0
µ
min
µ
µ
d
iameter. They occu
r
in
p
airs or small

g
rou
p
s and the cells of each
g
rou
p
ma
y
be derived from one ori
g
ina
l
e
pid
erma
l
ce
ll
. Usua
lly
t
h
e
y
move to t
h
e
h
emocoe

li
c
f
ace o
f
t
h
e
b
asa
ll
am
i
na, t
h
ou
gh in
some
i
nsects t
h
e
yf
orm c
l
usters
i
nt
h
e

h
emocoe
l
or m
ig
rate an
d
reassem
bl
ew
i
t
hi
nt
h
e
f
a
t
b
o
d
y. Oenocytes s
h
ow s
i
gns o
f
secretory act
i

v
i
ty t
h
at can
b
e corre
l
ate
d
w
i
t
h
t
h
emo
l
t
i
n
g
c
ycle, and, on the basis of certain staining reactions, it has been suggested that they produc
e
the li
p
o
p
rotein com

p
onent of e
p
icuticle. In addition, ultrastructural and biochemical studie
s
h
ave
l
e
d
to t
h
e
p
ro
p
osa
l
t
h
at t
h
ese ce
ll
s
p
ro
d
uce ec
dy

sone (Loc
k
e, 19
6
9; Romer, 1991). T
h
e
y
a
l
so s
y
nt
h
es
i
ze com
p
onents o
f
t
h
e cut
i
cu
l
ar wax,
i
nc
l

u
di
n
g
some contact sex
ph
eromone
s
(Blomquist and Dillwith, 198
5
; Schal et a
l.
, 1998). Derma
l
g
l
an
d
so
f
var
i
ous types are a
l
s
o
differentiated. In their simplest form the glands are unicellular and have a long duct tha
t
p
enetrates the cuticle to the exterior. More commonly, they are composed of several cells.

3
5
7
THE INTE
GU
MEN
T
The gland cells again exhibit cyclical activity associated with new cuticle production, an
d
i
t has been
p
ro
p
osed that the
y
secrete the cement la
y
er of e
p
icuticle.
T
h
e cut
i
c
l
e, w
hi
c

hi
sma
i
n
ly p
ro
d
uce
dby
t
h
ee
pid
erma
l
ce
ll
s, usua
lly i
nc
l
u
d
es t
h
re
e
p
r
i

mar
yl
a
y
ers, t
h
e
i
nner
p
rocut
i
c
l
e, m
iddl
ee
pi
cut
i
c
l
e, an
d
outer cut
i
cu
li
nenve
l

o
p
e (Loc
k
e,
2001) (F
i
gure 11.2). In o
ld
er accounts o
f
t
h
e
i
ntegument t
h
e cut
i
cu
li
nenve
l
ope
i
s treate
d
a
s
part of the epicuticle. However, Locke (1998, 2001) has argued that, because of its distinc

t
ori
g
in, structure and functions, the cuticulin envelo
p
e should be considered se
p
arate from
th
ee
pi
cut
i
c
l
e. A
ll
t
h
ree
p
r
i
mar
yl
a
y
ers are
p
resent over most o

f
t
h
e
b
o
dy
sur
f
ace an
di
nt
h
e
cut
i
c
l
et
h
at
li
nes ma
j
or
i
nva
gi
nat
i

ons suc
h
as t
h
e
f
ore
g
ut,
hi
n
dg
ut, an
d
trac
h
eae. However
,
th
e procut
i
c
l
e
i
s very t
hi
nora
b
sent, an

d
certa
i
n components o
f
t
h
eep
i
cut
i
c
l
e may
b
e
m
issing, where flexibility or sensitivity is needed, for example, over sensory structures and
t
he lining of tracheoles. Only the cuticulin envelope is universally present, except for the
p
ores over c
h
emosens
ill
a(C
h
a
p
ter 12, Sect

i
on 4.1)
.
T
h
e
p
rocut
i
c
l
e(
=
fi
b
rous cut
i
c
l
e)
f
orms t
h
e
b
u
lk
o
f
t

h
e cut
i
c
l
ean
di
n most s
p
ec
i
es
i
s
diff
erent
i
ate
di
nto two zones, en
d
ocut
i
c
l
ean
d
exocut
i
c

l
e, w
hi
c
h diff
er mar
k
e
dl
y
i
nt
h
e
i
r
F
I
GU
RE 11.2.
El
ectron m
i
cro
g
ra
ph
ss
h
ow

i
n
gd
e
p
os
i
t
i
on o
f
t
h
et
h
ree
p
r
i
mar
yl
a
y
ers o
f
cut
i
c
l
e

in
C
a
l
po
d
e
s
ethliu
s
. [From M. Locke, 2001, The Wigglesworth lecture: Insects for studying fundamental problems in biology,
J. Insect P
h
ysio
l
.
47
:495–507. With permission from Elsevier.
]
358
CHAPTER
11
F
I
GU
RE 11.3
.
Diagram showing orientation of microfibers in lamellae of endocuticle. [From A.C. Neville and
S. Caveney, 19
6

9, Scara
b
ae
id b
eet
l
e exocut
i
c
l
easanopt
i
ca
l
ana
l
ogue o
f
c
h
o
l
ester
i
c
li
qu
id
crysta
l

s,
B
io
l
.Rev
.
44
:
5
31–
5
62. B
yp
ermission of Cambrid
g
e Universit
y
Press, London.
]
p
h
y
sical
p
ro
p
erties but onl
y
sli
g

htl
y
in their chemical com
p
osition. In some cuticles th
e
b
or
d
er
b
etween t
h
etwo
i
s not c
l
ear an
d
an
i
nterme
di
ate area
,
t
h
e mesocut
i
c

l
e
,i
sv
i
s
ibl
e.
Adj
acent to t
h
ee
pid
erma
l
ce
ll
s a narrow amor
ph
ous
l
a
y
er, t
h
e assem
bly
zone, ma
yb
e see

n
w
here chitin microfibers are deposited and oriented
.
T
he endocuticle is composed of lamellae (Figure 11.3). Electron microscopy reveal
s
that each lamella is made u
p
of a mass of microfibers arran
g
ed in a succession of
p
lanes, all
fib
ers
i
na
pl
ane
b
e
i
n
gp
ara
ll
e
l
to eac

h
ot
h
er. T
h
eor
i
entat
i
on c
h
an
g
es s
ligh
t
ly f
rom
pl
ane
to
pl
ane ma
ki
n
g
cut
i
c
l

e
lik
e
ply
woo
d
w
i
t
hh
un
d
re
d
so
fl
a
y
ers. T
h
e exocut
i
c
l
e
i
st
h
ere
gi

on
of
procut
i
c
l
ea
dj
acent to t
h
eep
i
cut
i
c
l
et
h
at
i
ssosta
bili
ze
d
t
h
at
i
t
i

s not attac
k
e
db
yt
he
molting fluid and is left behind with the exuvium at molting (Locke, 1974). Not only i
s
the exocuticle chemicall
y
inert, it is hard and extremel
y
stron
g
. It is, in fact,
p
rocuticle tha
t
h
as
b
een “tanne
d
” (Sect
i
on 3.3). Exocut
i
c
l
e

i
sa
b
sent
f
rom areas o
f
t
h
e
i
nte
g
ument w
h
er
e
fl
ex
ibili
t
yi
sre
q
u
i
re
d
,
f

or exam
pl
e, at
j
o
i
nts an
di
nterse
g
menta
l
mem
b
ranes, an
d
a
l
on
g
t
h
e
ec
d
ys
i
a
lli
ne. In many so

f
t-
b
o
di
e
d
en
d
opterygote
l
arvae t
h
e exocut
i
c
l
e
i
s extreme
l
yt
hin
and frequently cannot be distinguished from the epicuticle and cuticulin envelope
.
P
rocuticle is composed almost entirely of protein and chitin. The latter is a nitrogenous
p
ol
y

saccharide consistin
gp
rimaril
y
of
N
-
acet
y
l
-
D
-gl
ucosam
i
ne res
id
ues to
g
et
h
er w
i
t
ha
s
ma
ll
amount o
fgl

ucosam
i
ne
li
n
k
e
di
n
a
β
1,4 confi
g
urat
i
on (F
ig
ure 11.4). In ot
h
er wor
d
s
,
chi
t
i
n
i
s very s
i

m
il
ar to ce
ll
u
l
ose, anot
h
er po
l
ysacc
h
ar
id
eo
f
great structura
l
s
i
gn
i
ficance,
e
x
cept that the hydroxyl group of carbon atom 2 of each residue is replaced by an acetamid
e
g
rou
p

. Because of this confi
g
uration, extensive h
y
dro
g
en bondin
g
is
p
ossible between ad
j
a
-
c
ent c
hi
t
i
nmo
l
ecu
l
es w
hi
c
hli
n
k
to

g
et
h
er (
lik
ece
ll
u
l
ose) to
f
orm m
i
crofi
b
ers. C
hi
t
i
nma
k
e
s
F
I
GU
RE 11.4
.
T
h

ec
h
em
i
ca
l
structure o
f
c
hi
t
i
n
.
3
5
9
THE INTE
GU
MEN
T
u
p between 2
5
% and 60% of the dry weight of procuticle but is not found in the epicuticle
and cuticulin envelo
p
e. It is associated with the
p
rotein com

p
onent, bein
g
linked to
p
rotein
m
o
l
ecu
l
es
by
cova
l
ent
b
on
d
s,
f
orm
i
n
g
a
gly
co
p
rote

i
n com
pl
ex. Stu
di
es
h
ave s
h
own t
h
at t
h
e
epid
erm
i
s secretes more t
h
an a
d
ozen ma
j
or
p
rote
i
ns
i
nto t

h
e cut
i
c
l
e
i
n a care
f
u
lly
t
i
me
d
sequence, pro
b
a
bl
yun
d
er
h
ormona
l
contro
l
(Su
d
erman

e
ta
l.
, 2003). Interest
i
ng
l
y, cut
i
cu
l
a
r
proteins of similar molecular weights have been found in a range of insect species suggesting
t
hat the chemical nature of the cuticle has been stron
g
l
y
conserved throu
g
h evolution. The
am
i
no ac
id
com
p
os
i

t
i
on o
f
t
h
e
p
rote
i
ns
d
eterm
i
nes t
h
e
i
r
p
ro
p
ert
i
es. For exam
pl
e, en
d
ocu
-

ti
cu
l
ar
p
rote
i
ns are
g
enera
lly
r
i
c
hi
n
hyd
ro
ph
o
bi
cam
i
no ac
id
sw
i
t
hb
u

lky
s
id
ec
h
a
i
ns an
d
ar
e
l
oose
l
y pac
k
e
d
(not compact) mo
l
ecu
l
es. T
hi
s prov
id
es t
h
een
d

ocut
i
c
l
ew
i
t
hfl
ex
ibili
ty an
d
w
ill also facilitate “creep” (the ability of layers to slide over each other), hence intrastadial
g
rowth in soft-bodied insects such as caterpillars. Conversely, in hard, stiff exocuticle, it i
s
small, com
p
act amino acids that
p
redominate (He
p
burn, 1985).
I
nt
h
e exocut
i
c

l
e, a
dj
acent
p
rote
i
nmo
l
ecu
l
es are
li
n
k
e
d
to
g
et
h
er
by
a
q
u
i
none mo
l
ecu

l
e,
an
d
t
h
e cut
i
c
l
e
i
ssa
id
to
b
e tanne
d
(Sect
i
on 3.3). T
h
e tanne
d
(sc
l
erot
i
ze
d

) prote
i
n, w
hi
c
hi
s
known as “sclerotin,” comprises several different molecules. Resilin is a rubberlike material
found in cuticular structures that undergo springlike movements, for example, wing hinges,
t
he
p
roboscis of Le
p
ido
p
tera, the hind le
g
s of fleas (Cha
p
ter 14, Section 3.1.2.), and the
wi
n
g
-
hi
n
g
e
lig

ament t
h
at stretc
h
es
b
etween t
h
e
pl
eura
lp
rocess an
d
secon
d
ax
ill
ar
y
sc
l
er
i
t
e
(
Chapter 14, Sections 3.3.1 and 3.3.3) (Neville, 197
5
). Like rubber, resilin, when stretched,

i
s able to store the energy involved. When the tension is released, the stored energy is use
d
t
o return the protein to its original length.
I
n addition to these structural
p
roteins, enz
y
mes also exist in the cuticle, includin
g
ph
eno
l
ox
id
ases, w
hi
c
h
cata
ly
ze t
h
eox
id
at
i
on o

f dihyd
r
i
c
ph
eno
l
s use
di
nt
h
e tann
i
n
gp
roces
s
(
Sect
i
on 3.3). T
h
ese enz
y
mes a
pp
ear to
b
e
l

ocate
di
nor
j
ust
b
eneat
h
t
h
ee
pi
cut
i
c
l
e.
Avar
i
ety o
f
p
i
gments
h
ave
b
een
f
oun

di
nt
h
e cut
i
c
l
e (or
i
nt
h
eep
id
erm
i
s) w
hi
c
h
ma
y
g
ive an insect its characteristic color (Section 4.3). Also, in a few beetles and larvae an
d
p
u
p
ae of some Di
p
tera, mineralized calcium (as the carbonate) is de

p
osited,
p
resumabl
y
t
o
i
ncrease r
igidi
t
y
(Lesc
h
en an
d
Cut
l
er, 1994).
C
erta
i
n
p
rocesses occur at t
h
e sur
f
ace o
f

t
h
e cut
i
c
l
ea
f
ter
i
t
h
as
b
een
f
orme
d
,
f
o
r
e
xamp
l
e, secret
i
on an
d
repa

i
ro
f
t
h
ewax
l
ayer an
d
tann
i
ng o
f
t
h
e outer procut
i
c
l
e. T
h
us
,
a route of communication must remain open between the epidermis and cuticular surface.
This route takes the form of pore canals which are formed as the new procuticle is deposited
(
Section 3.1), and which ma
y
or ma
y

not contain a c
y
to
p
lasmic
p
rocess. Most often, the
cana
l
s
d
o not conta
i
n an extens
i
on o
f
t
h
ee
pid
erma
l
ce
ll b
ut
h
ave at
l
east one “fi

l
ament”
pro
d
uce
db
yt
h
ece
ll
. Loc
k
e (1974) suggeste
d
t
h
at t
h
efi
l
ament(s) m
i
g
h
t
k
eepac
h
anne
l

ope
n
i
n the newly formed cuticle until the latter hardens, and anchor the cells to the cuticle. In
some insects the pore canals become filled with cuticular material once epicuticle formation
(
includin
g
tannin
g
)iscom
p
lete. The
p
ore canals terminate immediatel
y
below the e
p
icuticle.
R
unn
i
n
gf
rom t
h
et
ip
so
f

t
h
e
p
ore cana
l
stot
h
e outer sur
f
ace o
f
t
h
ee
pi
cut
i
c
l
e are
lipid
-fi
ll
e
d
c
h
anne
l

s
k
nown as wax cana
l
s
.
The epicuticle is a composite structure produced partly by epidermal cells and partl
y
b
y specialized glands. It ranges in thickness from a fraction of a micrometer to several
m
icrometers and
g
enerall
y
com
p
rises three la
y
ers. The la
y
ers are, from outside to inside
,
cement, wax (t
h
ese are secrete
d
outs
id
et

h
e cut
i
cu
li
nenve
l
o
p
e), an
d
t
h
e so-ca
ll
e
dp
rote
i
n
epi
cut
i
c
l
e. T
h
e nature o
f
cement var

i
es, t
h
ou
gh i
t
i
s
lik
e
ly
to
b
ea
pp
rox
i
mate
ly
s
i
m
il
ar to
s
h
e
ll
ac. T
h

e
l
atter
i
sam
i
xture o
fl
accose an
dli
p
id
s. T
h
e cement
i
sun
d
ou
b
te
dl
ya
h
ar
d
,
protective layer in some insects. In others it appears to be more important as a sponge tha
t
360

CHAPTER
11
soaks up excess wax. The latter could quickly replace that lost, for example, by surface
abrasion. The wax is a com
p
lex mixture whose com
p
osition varies both amon
g
and within
s
p
ec
i
es, somet
i
mes over
diff
erent
b
o
dy
re
gi
ons o
f
t
h
e same
i

nsect, an
di
n some s
p
ec
i
es
seasona
ll
y. Genera
ll
y,
l
ong-c
h
a
i
n
h
y
d
rocar
b
ons an
df
atty ac
id
esters pre
d
om

i
nate, t
h
oug
h
v
aried proportions of alcohols, fatty acids, and sterols may also occur. In some species th
e
mixture has relatively few different components, whereas in others, for example
,
M
u
s
c
a
,
more than 100 com
p
ounds have been identified (Blom
q
uist and Dillwith, 1985; Jaco
b
et al.
,
1
997). Accor
di
n
g
to Loc

k
e (1974), w
i
t
hi
nt
h
ewax
l
a
y
er t
h
ree re
gi
ons can
b
e
di
st
i
n
g
u
i
s
h
e
d.
Adj

acent to t
h
e cut
i
cu
li
nenve
l
o
p
e
i
s a mono
l
a
y
er o
f
t
igh
t
ly p
ac
k
e
d
mo
l
ecu
l

es
i
n
liq
u
id
f
orm that gives the cuticular surface its high contact angle with water and its resistance t
o
w
ater loss (but see Section 4.2.). Most wax is in the middle layer, which is less ordered an
d
p
ermeates the cement. The outer wax la
y
er, which com
p
rises cr
y
stalline wax blooms, i
s
not
p
resent
i
na
ll i
nsects. T
h
e

i
nnermost
l
a
y
er o
f
t
h
ee
pi
cut
i
c
l
e, t
h
e
p
rote
i
ne
pi
cut
i
c
l
e,
li
e

s
b
eneat
h
t
h
e cut
i
cu
li
nenve
l
o
p
e. It ma
yb
e severa
l
m
i
crometers t
hi
c
k
an
d lik
et
h
e cut
i

cu
li
n
enve
l
ope
i
t covers a
l
most a
ll
o
f
t
h
e sur
f
ace o
f
t
h
e
i
nsect. It
i
sa
b
sent
f
rom trac

h
eo
l
es an
d
p
arts of some sense organs. It comprises dense, amorphous protein tanned in a manne
r
similar to the
p
rotein of the exocuticle (Section 3.3) but contains no chitin.
Th
e cut
i
cu
li
nenve
l
o
p
e(a
b
out 20 nm t
hi
c
k
) exten
d
s over t
h

e ent
i
re
b
o
dy
sur
f
ace an
d
ecto
d
erma
li
nva
gi
nat
i
ons,
i
nc
l
u
di
n
g
t
h
e most m
i

nute trac
h
eo
l
es,
b
ut
i
sa
b
sent
f
rom s
p
ec
i
fic
areas o
f
sense organs an
df
rom t
h
et
i
ps o
f
certa
i
ng

l
an
d
ce
ll
s. It may
b
e cons
id
ere
d
t
he
most important layer of the cuticle for the following reasons (Locke, 1974, 2001). (1) It is a
selectivel
yp
ermeable barrier. Durin
g
breakdown of the old cuticle, it allows the “activatin
g
f
actor” for the molting gel to move out and the products of cuticular hydrolysis to enter, yet
ff
i
t
i
s
i
m
p

ermea
bl
etot
h
e enz
y
mes
i
nt
h
emo
l
t
i
n
gfl
u
id
.It
i
s
p
ermea
bl
e to waxes (as t
h
ese are
d
epos
i

te
d
on
l
ya
f
ter t
h
e cut
i
cu
li
n
l
ayer
h
as
f
orme
d
)an
d
,
i
n some
i
nsects,
i
t perm
i

ts t
h
e entry
o
f water. (2) It is inelastic and, therefore, serves as a limiter of growth. (3) It provides th
e
base on which the wax monolayer sits. The nature of the cuticulin envelope will therefore
determine whether the wax molecules are oriented with their
p
olar or non
p
olar
g
rou
p
s
f
ac
i
n
g
outwar
d
an
d
,t
h
ere
f
ore, t

h
e sur
f
ace
p
ro
p
ert
i
es o
f
t
h
e cut
i
c
l
e. (4) It
pl
a
y
saro
l
e
in
determining the surface pattern of the cuticle. (
5
) It is resistant to abrasion and helps prevent
infection. (6) It is involved in production of physical colors. Despite the importance of th
e

c
uticulin envelope, its composition is largely unknown.
3.
C
ut
i
cle Format
i
o
n
F
ormation of new cuticle (Figure 11.
5
) may be viewed largely as a succession of
s
y
ntheses b
y
e
p
idermal cells, with dermal
g
lands and oenoc
y
tes addin
g
their
p
roducts at
t

h
ea
pp
ro
p
r
i
ate moment (Loc
k
e, 1974). It must
b
e rea
li
ze
d
,
h
owever, t
h
at ot
h
er, re
l
ate
d
p
rocesses suc
h
as
di

sso
l
ut
i
on o
f
o
ld
cut
i
c
l
e are go
i
ng on concurrent
l
yan
d
t
h
at cut
i
c
l
e
f
ormation is partly a preecdysial and partly a postecdysial event; that is, much endocuticl
e
f
ormation, tanning of the outer procuticle, wax secretion, and other processes occur after

the remains of the old cuticle are shed.
3
.1. Preecd
y
sis
In most species the onset of a molting cycle is marked by an increase in the volume
o
f the e
p
idermal cells and/or b
y
e
p
idermal mitoses. These events are soon followed b
y
36
1
THE INTE
GU
MEN
T
F
IGURE 11.5
.
Summary o
f
cut
i
c
l

e
f
ormat
i
on
d
ur
i
ng t
h
emo
l
t
/i
ntermo
l
tcyc
l
e. In
di
v
id
ua
l
components are no
t
drawn to scale. The numbers in Fi
g
ure 11.
5

B indicate the se
q
uence of actions resultin
g
in
p
la
q
ue di
g
estion. (A)
S
ecretion of ecdysial droplets. (B) Pinocytosis and apolysis of plasma membrane. (C) Redifferentiation of plaques
an
d
cut
i
cu
li
nenve
l
ope
d
epos
i
t
i
on. (D) Cut
i
cu

li
nenve
l
ope comp
l
ete an
ddi
gest
i
on o
f
o
ld
cut
i
c
l
e. (E) Secret
i
on o
f
i
nner e
pi
cut
i
c
l
ean
db

uc
ki
n
g
o
f
cut
i
cu
li
nenve
l
o
p
e. (F) Be
gi
nn
i
n
g
o
fp
rocut
i
c
l
e secret
i
on. (G) Cut
i

c
l
e
i
mme
di
ate
ly
after ecdysis. (H) Cuticle after tanning
.
362
CHAPTER
11
apolysis, the detachment of the epidermis from the old cuticle. The epidermal cells, at this
time, show si
g
ns of
p
re
p
aration for future s
y
nthetic activit
y
. One or more nucleoli become
p
rom
i
nent, t
h

e num
b
er o
f
r
ib
osomes
i
ncreases, an
d
t
h
er
ib
onuc
l
e
i
cac
id
content o
f
t
h
ece
ll
s
i
se
l

evate
d
. Two com
p
onents o
f
t
h
ee
pid
erma
l
ce
ll
s are es
p
ec
i
a
lly i
m
p
ortant, name
ly
,t
he
Go
l
g
i

comp
l
exes an
d
t
h
ep
l
asma mem
b
rane p
l
aques, w
h
ose act
i
v
i
t
i
es a
l
ternate to create t
h
e
new cuticle. Just prior to apolysis, Golgi complex activity increases, and the vesicles pro-
duced mi
g
rate to the a
p

ical
p
lasma membrane where the
y
release their contents—ecd
y
sial
dro
p
lets—between the e
p
idermal microvilli (Fi
g
ure 11.5A). The ecd
y
sial dro
p
lets contai
n
p
rote
i
nases an
d
c
hi
t
i
nases
f

or cut
i
c
l
e
dig
est
i
on, t
h
ou
gh
t
h
e enz
y
mes rema
i
n
i
nan
i
nact
i
ve
f
orm unt
il
a
f

ter
f
ormat
i
on o
f
t
h
e new cut
i
cu
li
nenve
l
ope w
h
en t
h
eep
id
erma
l
ce
ll
s secrete a
n
“activation factor.” I
n
C
a

lp
o
d
es et
hl
iu
s
large quantities of an amidase are generated by th
e
epidermis and fat body during the intermolt. The amidase (in its inactive form) accumulates
i
nt
h
e
h
emo
ly
m
ph
unt
il
t
h
emo
l
tc
y
c
l
e

b
e
gi
ns, w
h
en
i
t moves
i
nto t
h
emo
l
t
i
n
gfl
u
id
an
di
sac
-
t
i
vate
d
, ena
bli
n

gp
rec
i
se
i
n
i
t
i
at
i
on o
f
cut
i
c
l
e
b
rea
kd
own (Marcu an
d
Loc
k
e, 1999). Betwee
n
8
0% an
d

90% o
f
t
h
eo
ld
cut
i
c
l
e
i
s
di
geste
d
an
d
may
b
e reuse
di
nt
h
e pro
d
uct
i
on o
f

new
c
uticle. In earlier accounts it was assumed that the molting fluid, including the breakdow
n
p
roducts, were resorbed across the body wall. However, recent studies have demonstrated
that most of the moltin
g
fluid is recovered b
y
both oral and anal drinkin
g
, reenterin
g
the
b
o
dy
cav
i
t
yby
a
b
sor
p
t
i
on across t
h

em
idg
ut wa
ll
(Yarema
et al.
, 2000). T
h
e exocut
i
c
l
e
,
musc
l
e
i
nsert
i
ons, an
d
sensory structures
i
nt
h
e
i
ntegument are not
d

egra
d
e
db
ymo
l
t
i
n
g
fl
uid. Thus, an insect is able to move and receive information from the environment more
o
r less to the point of ecdysis
.
After release of the ecd
y
sial dro
p
lets, the microvilli are withdrawn and their
p
la
q
ue
s
are
p
inoc
y
tosed and di

g
ested in multivesicular bodies (Fi
g
ure 11.5B). New microvilli
,
wi
t
hpl
a
q
ues at t
h
e
i
rt
ip
s, t
h
en
diff
erent
i
ate. T
h
e first
l
a
y
er o
f

new cut
i
c
l
e
d
e
p
os
i
te
di
st
h
e
c
ut
i
cu
li
nenve
l
ope. M
i
nute convex patc
h
es o
f
cut
i

cu
li
n appear a
b
ove t
h
ep
l
aques (F
i
gure
1
1.
5
C), the patches eventually fusing together to form a continuous but buckled layer
(Fi
g
ure 11.5D). The bucklin
gp
ermits ex
p
ansion of the cuticle after moltin
g
and is also
im
p
ortant in the formation of annuli and taenidia in tracheae and tracheoles (Cha
p
ter 15
,

S
ect
i
on 2.1). Ot
h
er
b
uc
kli
n
gp
atterns
d
eterm
i
ne t
h
es
p
ec
i
fic sur
f
ace structure o
f
sca
l
es
,
b

r
i
st
l
es, an
d
m
i
crotr
i
c
hi
a. Oenocytes are max
i
ma
ll
y act
i
ve at t
hi
st
i
me, an
di
t
i
s poss
ible
that they are involved in cuticulin formation, perhaps by synthesizing a precursor for the
epidermal cells. When the envelope is complete, it becomes tanned. The Golgi complexe

s
then show renewed activit
y
, their vesicles dischar
g
in
g
their contents to form the inne
r
(
p
rotein) e
p
icuticle (Fi
g
ure 11.5E)
.
B
e
f
ore t
h
e
i
nner ep
i
cut
i
c
l

e
i
s
f
u
ll
y
f
orme
d
pro
d
uct
i
on an
dd
epos
i
t
i
on o
f
t
h
e new procu-
ticle begin. In contrast to the epicuticle, whose layers are produced sequentially from inside
to outside, the new procuticle is produced with the newest layers on the inside. Again, i
t
is the
p

lasma membrane
p
la
q
ues that are involved, new chitin fibers arisin
g
on their oute
r
surface (Fi
g
ure 11.5F,G). However, details of the mechanism b
y
which new
p
rocuticle i
s
p
ro
d
uce
d
rema
i
ns
k
etc
hy
.T
h
ee

pid
erma
l
ce
ll
s conta
i
nt
h
e enz
y
mes necessar
yf
or s
y
nt
h
es
is
o
f acetylglucosamine from trehalose. Acetylglucosamine units perhaps are then secreted
into the apolysial space, polymerization into chitin being promoted by the enzyme chiti
n
s
y
nthetase attached to the
p
lasma membrane
p
la

q
ues. Some
p
rocuticular
p
roteins are s
y
n-
t
h
es
i
ze
dby
t
h
ee
pid
erma
l
ce
ll
sw
hil
eot
h
ers are ac
q
u
i

re
df
rom t
h
e
h
emo
ly
m
ph
(Sas
s
et al.
,
1
993
;
Su
d
erma
n
e
ta
l.
, 2003). How t
h
e
p
rote
i

ns
b
ecome
i
ncor
p
orate
di
nto t
h
e
p
rocut
i
c
l
e
rema
i
ns unc
l
ear
.
363
THE INTE
GU
MEN
T
Deposition of the wax layer of the epicuticle begins some time prior to ecdysis. For
e

xam
p
le, i
n
B
lattella germanica oenoc
y
tes associated es
p
eciall
y
with the inte
g
ument of
a
bd
om
i
na
l
stern
i
tes 3–
6b
ecome ma
j
or
p
ro
d

ucers o
f hyd
rocar
b
ons ear
ly i
nt
h
emo
l
tc
y-
c
l
e. T
h
e
hyd
rocar
b
ons are store
di
n
f
at
b
o
dy
,t
h

en trans
p
orte
d
to t
h
ee
pid
erm
i
s
b
oun
d
t
o
li
pop
h
or
i
na
f
ew
d
ays
b
e
f
ore mo

l
t
i
ng occurs (Sc
h
a
l
et a
l.
, 1998; Youn
g
e
ta
l.
, 1999). T
he
wa
xis
s
ecreted by the epidermal cells, probably as lipid-water liquid crystals, and passes
alon
g
the
p
ore canals to the outside. Wax
p
roduction continues after ecd
y
sis and, in some
i

nsects, t
h
rou
gh
out t
h
e ent
i
re
i
ntermo
l
t
p
er
i
o
d
an
di
nt
h
ea
d
u
l
t sta
g
e
.

3.2. Ecdys
i
s
At the time of ecdysis, the old cuticle comprises only the original exocuticle and
ep
icuticle. In man
y
insects it is se
p
arated from the new cuticle b
y
an air s
p
ace and
a
thi
nec
dy
s
i
a
l
(a
p
o
ly
s
i
a
l

) mem
b
rane t
h
at
i
s
f
orme
df
rom un
dig
este
di
nner
l
a
y
ers o
f
t
h
e
e
n
d
ocut
i
c
l

e. T
h
ese
l
ayers are not
di
geste
db
ecause t
h
ey
b
ecame tanne
d
a
l
ong w
i
t
h
t
h
ene
w
cuticulin envelope. Shortly before molting an insect begins to swallow air (or water, if
aquatic), thereby increasing the hemolymph pressure by as much as 12 kPa. Hemolymph
i
s then localized in the head and thorax followin
g
contraction of interse

g
mental abdominal
m
usc
l
es. In man
yi
nsects t
h
ese musc
l
es
b
ecome
f
unct
i
ona
l
on
ly
at t
h
et
i
me o
f
ec
dy
s

i
san
d
hi
sto
ly
ze a
f
ter eac
h
mo
l
t. T
h
e
l
oca
li
ncrease
i
n
p
ressure
i
nt
h
e anter
i
or
p

art o
f
t
h
e
b
o
dy
causes the old cuticle to split along a weak ecdysial line where the exocuticle is thin o
r
absent. An insect continues to swallow air or water after the molt in order to stretch the ne
w
cuticle
p
rior to tannin
g
.
3.3. Postecd
y
sis
S
everal processes are continued or initiated after ecdysis. As noted wax secretion con-
t
inues, and the ma
j
or
p
ortion of the endocuticle is de
p
osited at this time. Indeed, endocuticle

p
ro
d
uct
i
on
i
n some
i
nsects a
pp
ears to
b
e a more or
l
ess cont
i
nuous
p
rocess t
h
rou
gh
out t
h
e
i
ntermo
l
t

p
er
i
o
d
.It
i
sa
l
so at t
hi
st
i
me t
h
at t
h
e
d
erma
lgl
an
d
sre
l
ease t
h
e cement.
T
h

e most str
iki
ng postec
d
ys
i
a
l
event,
h
owever,
i
st
h
e
diff
erent
i
at
i
on o
f
t
h
e exocut
i
c
l
e,
t

hat is, the hardening of the outer procuticle (Figure 11.
5
H). This results from a biochemical
process known as tanning (sclerotization), in which proteins become covalently bound to
e
ach other (and hence stabilized) b
y
means of
q
uinones. Hardenin
g
is usuall
y
accom
p
anied
by d
ar
k
en
i
n
g
(me
l
an
i
zat
i
on), t

h
ou
gh
t
h
etwoma
yb
e
di
st
i
nct
p
rocesses; t
h
at
i
s, some s
p
ec
i
es
h
ave pa
l
e
b
ut very
h
ar

d
cut
i
c
l
es. T
h
oug
h
tann
i
ng
i
s
di
scusse
dh
ere
i
nt
h
e context o
f
t
h
e
cuticle, it should be noted that it also an important process in the final structure of insect
egg
shells, egg cases (oothecae) and protective froths, cocoons, puparia and various sil
k

structures. Indeed, much of the basic understandin
g
of tannin
g
came from studies usin
g
t
he cockroach ootheca and the fl
yp
u
p
arium (Andersen, 1985; Ho
p
kins and Kramer, 1992)
.
More recent
ly
,t
h
e cut
i
c
l
es o
f
t
he
Man
d
uca

s
exta
p
u
p
aan
d
o
fl
ocusts an
dg
rass
h
o
pp
ers
h
av
e
prove
d
to
b
e exce
ll
ent mo
d
e
l
s

f
or stu
d
yo
f
t
hi
s process. T
h
oug
h
t
h
e
d
eta
il
s may
diff
er,
i
t
i
s now possible to provide a basic scheme for the events that culminate in a tanned cuticl
e
(
Fi
g
ure 11.6)
.

Be
f
ore tann
i
n
gb
e
gi
ns, t
h
e
l
eve
l
o
f
t
h
eam
i
no ac
id
t
y
ros
i
ne
i
nt
h

e
h
emo
ly
m
ph i
ncreases.
T
h
et
y
ros
i
ne
i
s most
ly b
oun
d
to
gl
ucose,
ph
os
ph
ate, or su
lph
ate,
f
orm

i
n
g
water-so
l
u
bl
e
con
j
ugates. T
hi
s
i
st
h
oug
h
tto
i
ncrease t
h
e amount o
f
tyros
i
ne t
h
at can
b

e carr
i
e
di
nt
he
36
4
CHAPTER
11
F
I
GU
RE 11.6.
S
ummar
y
o
f
t
h
e tann
i
n
gp
rocess.
h
emo
l
ymp

h
, to protect
i
t
f
rom ox
id
at
i
on, an
d
to prevent
i
ts use
i
n compet
i
ng meta
b
o
li
c
p
athways. In a few species the tyrosine accumulates within fat-body vacuoles, particularly
as the dipeptide
N
-
β
-
alanyltyrosine. The tyrosine is converted to “dopa” (dihydroxypheny

-
l
alanine) which is then decarbox
y
lated formin
g
do
p
amine,
N
-
β
-alan
y
ldo
p
amine, and othe
r
c
atec
h
o
l
am
i
nes (Ho
pki
ns an
d
Kramer, 1992; Ho

pki
ns
et al.
, 1999). L
ik
et
y
ros
i
ne, t
h
e cat
-
ec
h
o
l
am
i
nes occur as con
j
ugates an
d
accumu
l
ate
i
nt
h
e

h
emo
l
ymp
h
.On
l
yw
h
en t
h
e cat
-
echolamines are taken up by the epidermal cells are the conjugates released. Within th
e
epidermis, catecholamines are converted to the corresponding
N
-acetyl derivatives which
then move via the
p
ore canals to the e
p
icuticle where the
y
are oxidized to
q
uinones under th
e
i
n

fl
uence o
fph
eno
l
ox
id
ases. Two
di
st
i
nct
ph
eno
l
ox
id
ases
h
ave
b
een
i
so
l
ate
df
rom cut
i
c

l
e,
tyros
i
nase, an
dl
accase. Tyros
i
nase may
b
e
i
nvo
l
ve
di
n tann
i
ng
i
n some s
i
tuat
i
ons
b
ut
is
l
ikely more important in wound healing (Chapter 17, Section

5
.1). By contrast, the activit
y
o
f laccase is closely correlated with the period of tanning, and this enzyme is therefore as-
sumed to
p
la
y
the ma
j
or role in the s
y
nthesis of
q
uinone tannin
g
a
g
ents. The
q
uinones diffus
e
b
ac
ki
nto t
h
e
p

rocut
i
c
l
ean
dli
n
kp
rote
i
nmo
l
ecu
l
es to
g
et
h
er. Accor
di
n
g
to Hac
k
man (1974)
,
q
u
i
nones ma

yp
o
ly
mer
i
ze, a
p
rocess t
h
at ma
k
es t
h
em
l
ar
g
er, more e
ff
ect
i
ve tann
i
n
g
a
g
ents.
Th
epo

l
ymer w
ill h
ave more react
i
ve s
i
tes an
db
e capa
bl
eo
fb
r
id
g
i
ng
l
arger
di
stances, t
he
result being that more protein molecules can be linked. The quinones combine covalently
w
ith the terminal amino
g
rou
p
or a sulfh

y
dr
y
l
g
rou
p
of the
p
rotein to form a
n
N
-
catechol
365
THE INTE
GU
MEN
T
protein, which in the presence of excess quinone is oxidized to a
n
N
-
quinonoid protein. Th
e
latter is able to react with the terminal amino
g
rou
p
or sulfh

y
dr
y
l
g
rou
p
of another
p
rotei
n
t
o
li
n
k
t
h
etwomo
l
ecu
l
es. In a num
b
er o
f
s
p
ec
i

e
s
β
-
a
l
an
i
ne
i
s
i
ncor
p
orate
di
nto t
h
e cut
i
c
l
e
d
ur
i
n
g
tann
i

n
g
,an
di
t
i
ss
p
ecu
l
ate
d
t
h
at t
hi
sam
i
no ac
id b
ecomes attac
h
e
d
to
p
rote
i
ns,
l

eav-
i
ng
i
ts am
i
no term
i
nus
f
ree to part
i
c
i
pate
i
n
li
n
ki
ng t
h
equ
i
none an
d
prote
i
n. In a
ddi

t
i
on,
t
he quinone can react with th
e
ε
-amino groups of lysine residues in the protein molecule to
e
ffect further bindin
g
. Autotannin
g
is also a
p
ossibilit
y
. This is the oxidation of aromatic
am
i
no ac
id
s (e.
g
., t
y
ros
i
ne) w
i

t
hi
na
p
o
lyp
e
p
t
id
ec
h
a
i
nto
f
orm
q
u
i
none com
p
oun
d
st
h
at
can su
b
se

q
uent
ly li
n
k
w
i
t
h
am
i
no
g
rou
p
s
i
na
dj
acent c
h
a
i
ns. T
h
ou
gh
autotann
i
n

gh
as neve
r
b
een
d
emonstrate
d
,“
d
opa”
h
as
b
een
f
oun
di
n sma
ll
amounts
i
n certa
i
n cut
i
cu
l
ar prote
i

ns o
f
Man
d
uca
s
ext
a
(
Okot-Kotber
e
ta
l.
,
1
994) and presumably could engage in cross-linkin
g
r
eactions.
T
h
eco
l
or o
f
tanne
d
cut
i
c

l
e
d
e
p
en
d
sont
h
e amount o
f
o
-q
u
i
none t
h
at
i
s
p
resent. W
h
e
n
thi
smo
l
ecu
l

e
i
s
p
resent
i
n sma
ll q
uant
i
t
i
es t
h
e cut
i
c
l
e
i
s
p
a
l
e;
if i
t
i
s
i

n excess, an
d
es
p
ec
i
a
lly
if i
tpo
l
ymer
i
zes, t
h
e cut
i
c
l
ew
h
en tanne
di
s
d
ar
k
. In some cut
i
c

l
es pro
d
uct
i
on o
f
t
h
ec
h
arac-
t
eristic dark brown or black color (melanization) is entirely separate from tanning, although
i
t involves tyrosine and its oxidation product dopa. Oxidation of dopa yields dopaquinone
w
hich can form an indole rin
g
derivative, do
p
achrome. Decarbox
y
lation, oxidation, and
p
o
ly
mer
i
zat

i
on t
h
en occur to
p
ro
d
uce t
h
e
pig
ment me
l
an
i
n.
As tann
i
ng occurs, t
h
e cut
i
c
l
eun
d
ergoes a num
b
er o
f

p
h
ys
i
ca
l
rearrangements. Its wate
r
content decreases as a result of (1) a decline in the number of hydrophilic groups such a
s
-
NH
2
b
ecause of their involvement in tanning and (2) a tighter packing of the chitin and
p
rote
i
nmo
l
ecu
l
es. T
hi
s
l
ea
d
stoanovera
ll d

ecrease
i
nt
h
et
hi
c
k
ness o
f
t
h
e cut
i
c
l
e.
3.4.
C
oord
i
nat
i
on o
f
Events
I
t is essential that the complex series of events comprising a molt cycle be coordinated.
Central to this coordination are hormones (Cha
p

ter 13, Section 3), thou
g
h the ex
p
ression of
th
e
i
re
ff
ects can
b
emo
di
fie
dby
ot
h
er
f
actors,
f
or exam
pl
e, nutr
i
t
i
on an
di

n
j
ur
y
. Man
y
events
wi
t
hi
namo
l
tcyc
l
e are
i
n
fl
uence
db
y
h
ormones,
b
ut st
ill
unc
l
ear
i

sw
h
et
h
er t
hi
s
i
n
fl
uence
is
d
irect or indirect; that is, do hormones directly regulate all of these events or merely initiate
a cascade of reactions? The picture is further complicated because more than one hormone
m
a
y
influence the same event
.
β
-Ec
dy
sone a
ff
ects man
y
events t
h
rou

gh
outamo
l
tc
y
c
l
e. It
i
n
i
t
i
ates a
p
o
ly
s
i
s, st
i
mu-
l
ates e
pid
erma
l
ce
ll
m

i
tos
i
s,
i
ncreases c
hi
t
i
nase act
i
v
i
t
y
,
p
romotes t
h
es
y
nt
h
es
i
so
f
se
l
ect

e
pidermal cell proteins, triggers release of tyrosine from its conjugates, and induces th
e
synthesis of several enzymes involved in tanning. Further, the development and activity of
t
he e
p
idermal feet are correlated with chan
g
in
g
hemol
y
m
p
h ecd
y
sone levels in the final lar-
val
i
nstar. Amon
g
t
h
e ear
li
est stu
di
es o
f

t
h
es
i
te o
f
act
i
on o
f
ec
dy
sone were t
h
ose o
f
Kar
l
so
n
e
ta
l
. (see references in Neville, 1975), s
p
ecificall
y
in relation to tannin
g
. Ecd

y
sone stim-
ul
ates synt
h
es
i
so
fd
opa
d
ecar
b
oxy
l
ase mRNA. Kar
l
son’s group suggeste
d
t
h
at ec
d
ysone
acted on the epidermal cells and this is supported b
y
i
n vitr
o
studies on isolated epidermis.

However, for some s
p
ecies, it also seems likel
y
that the hemoc
y
tes are a tar
g
et or
g
an. Mor
e
r
ecent
ly
,t
h
ea
bili
t
y
o
f
β
-ec
dy
sone to
i
n
d

uce t
h
eex
p
ress
i
on o
fg
enes
f
or ot
h
er
k
e
y
mo
l
ecu
l
e
s
i
nt
h
emo
l
tc
y
c

l
e
h
as
b
een s
h
own,
f
or exam
pl
e,
f
or c
hi
t
i
nase (Z
h
en
g
e
ta
l.
, 2003). It a
pp
ear
s
th
at genes assoc

i
ate
d
w
i
t
h
t
h
emo
l
tcyc
l
e
diff
er
i
nt
h
e
i
r sens
i
t
i
v
i
ty to t
h
e

h
ormone, som
e
b
eing switched on at low (or decreasing) concentrations, others requiring higher (or in
-
creasing) titers for their expression. In this way, varying amounts o
f
β
-ecdysone throughou
t
366
CHAPTER
11
the molt cycle serve to synchronize the many steps and processes that occur. It must be
noted tha
t
β
-ecd
y
sone does not act directl
y
on
g
enes; rather, it binds with rece
p
tors in the
nuc
l
ear mem

b
rane caus
i
n
g
re
l
ease o
f
secon
d
messen
g
ers (e.
g
., c
y
c
li
c AMP) w
h
ose act
i
on
t
h
en st
i
mu
l

ates gene express
i
on.
T
hough the modifying influence of juvenile hormone on ecdysone effects has been
k
nown for a considerable time (Chapter 21, Section 6.1), it has been shown only recentl
y
that it, too, acts on the
g
enome. Its effect is to
p
ro
g
ram the e
p
idermis to secrete a cuticle
ch
aracter
i
st
i
co
f
t
h
e
j
uven
il

e sta
g
e. L
ik
e β
-
ec
dy
sone,
j
uven
il
e
h
ormone
bi
n
d
sw
i
t
h
nuc
l
ear
rece
p
tors to
p
rec

ipi
tate, v
i
a a secon
d
messen
g
er, react
i
ons
l
ea
di
n
g
to
g
ene ex
p
ress
i
on.
B
ursicon, like ecdysone, affects many processes, though all are related to tannin
g
and melanization of the cuticle. Bursicon’s primary effect appears to be to increase the
p
ermeabilit
y
of the hemoc

y
te wall to t
y
rosine and the e
p
idermal cell wall to do
p
amine. Th
e
h
ormone ma
y
exert t
hi
se
ff
ect v
i
aac
y
c
li
c AMP-me
di
ate
d
s
y
stem. In a
ddi

t
i
on,
b
urs
i
con
ma
y
act
i
vateat
y
ros
i
nase
i
n
h
emoc
y
tes, w
hi
c
h
cata
ly
zes t
h
eox

id
at
i
on o
f
t
y
ros
i
ne to
d
o
p
a.
Fi
na
ll
y, ec
d
ys
i
s
i
sregu
l
ate
db
yanec
l
os

i
on
h
ormone secrete
db
yt
h
e
b
ra
i
n
i
ns
ilk
mot
h
s
(Chapter 21, Section 6.2) and wax synthesis and endocuticle deposition require the presenc
e
o
f the cor
p
us allatum/cor
p
us cardiacum com
p
lex i
n
Cal

p
odes ethlius
.
4
. Funct
i
ons o
f
the Integument
Most functions of the integument relate to the physical structure of the cuticle thoug
h
t
h
e
l
atter ma
y
serve as a source o
f
meta
b
o
li
tes
d
ur
i
n
gp
er

i
o
d
so
f
starvat
i
on. T
h
e
p
r
i
mar
y
f
unct
i
ons ma
yb
e
di
scusse
d
un
d
er t
h
ree
h

ea
di
n
g
s: stren
g
t
h
an
dh
ar
d
ness,
p
ermea
bili
t
y
,an
d
p
ro
d
uct
i
on o
f
co
l
or.

4
.1.
S
tren
g
th and Hardnes
s
Th
e
f
ew stu
di
es t
h
at
h
ave
b
een carr
i
e
d
out on t
h
e mec
h
an
i
ca
lp

ro
p
ert
i
es o
fi
nsect cut
i
c
le
i
n
di
cate t
h
at
i
so
f
me
di
um r
i
g
idi
ty an
dl
ow tens
il
e strengt

h
(Loc
k
e, 1974). T
h
ere
i
s,
h
owever
,
w
ide variation from this general statement; for example, the cuticles of most endopterygot
e
l
arvae are extremely plastic, whereas the mandibular cuticle of many biting insects may be
extremel
y
hard, enablin
g
them to bite throu
g
h metal. Further, there is an obvious difference
i
n
p
ro
p
ert
i

es
b
etween sc
l
er
i
tes an
di
nterse
g
menta
l
mem
b
ranes, an
db
etween t
ypi
ca
l
non
-
e
l
ast
i
c cut
i
c
l

ean
d
t
h
at w
hi
c
h
conta
i
ns a
high p
ro
p
ort
i
on o
f
res
ili
n.
T
hough the above properties indicate that the cuticle is satisfactory as a “skin” pre
-
v
e
nting physical damage to internal organs, discussion of the suitability of the cuticle as
a
skeletal com
p

onent must include an a
pp
reciation of overall bod
y
structure (Locke, 1974).
M
ost com
p
onents o
fi
nsect (an
d
ot
h
er art
h
ro
p
o
d
)
b
o
di
es ma
yb
e cons
id
ere
d

as cut
i
cu
l
ar
cyli
n
d
ers or s
ph
eres. Suc
h
atu
b
u
l
ar s
h
e
ll
(use
dh
ere
i
nt
h
een
gi
neer
i

n
g
sense to mean a
surface-supporting structure that is thin in relation to total size) is about three times as
strong as a solid rod of the same material having the same cross-sectional area as the shell
(i.e., the
y
both contain the same amount of skeletal material). The force re
q
uired to dis
-
tort t
h
es
h
e
ll i
s
p
ro
p
ort
i
ona
l
to t
h
et
hi
c

k
ness o
f
t
h
es
h
e
ll
an
di
nverse
ly p
ro
p
ort
i
ona
l
to t
he
c
ross-sect
i
ona
l
area o
f
t
h

ew
h
o
l
e
b
o
dy
.T
h
us,
i
n sma
ll
or
g
an
i
sms w
h
ere t
h
et
hi
c
k
ness o
f
t
h

es
h
e
ll i
s great re
l
at
i
ve to t
h
e cross-sect
i
ona
l
area o
f
t
h
e
b
o
d
y, t
h
e use o
f
as
h
e
ll

as an
e
xoskeletal structure is quite feasible. In larger organisms the advantage of the extra strengt
h
367
THE INTE
GU
MEN
T
r
elating to a shell type of skeleton is greatly outweighed (literally as well as metaphori-
call
y
)b
y
the massive increase in thickness of the shell that would be re
q
uired and,
p
erha
p
s,
by
t
h
e
phy
s
i
o

l
o
gi
ca
lp
ro
bl
ems o
fp
ro
d
uc
i
n
g
t
h
e
l
ar
g
e amounts o
f
mater
i
a
l
re
q
u

i
re
df
or
i
t
s
construct
i
on
.
4.2. Permeab
i
l
i
t
y
For
different insects there exists a wide ran
g
e of materials that are
p
otential
p
ermeant
s
o
f
t
h

e
i
nte
g
ument, an
d
o
ff
actors t
h
at a
ff
ect t
h
e
i
r rate o
fp
ermeat
i
on. Somet
i
mes s
p
ec
i
fi
c
r
e

gi
ons o
f
t
h
e
i
nte
g
ument are constructe
d
to
f
ac
ili
tate entr
y
or ex
i
to
f
certa
i
n mater
i
a
l
s; mor
e
o

f
ten t
h
e
i
ntegument
i
s structure
d
to prevent entry or
l
oss. At t
hi
st
i
me we s
h
a
ll
cons
id
er
only the permeability of the cuticle to water and insecticides, of which the latter may now be
considered a normal hazard for most insects. The
p
assa
g
eof
g
ases throu

g
h the inte
g
umen
t
i
s considered in Cha
p
ter 15.
W
ater.
W
ater may be either lost or gained through the integument. In terrestrial
WW
i
nsects, which exist in humidities that are almost always less than saturation, the problem
i
s to prevent loss through evaporation. In freshwater forms the problem is to prevent entry
r
elated to osmosis.
I
n man
y
terrestr
i
a
li
nsects t
h
e rate o

f
eva
p
orat
i
ve water
l
oss
i
s
p
ro
b
a
bly l
ess t
h
an 1%
per
h
our o
f
t
h
e tota
l
water content o
f
t
h

e
b
o
d
y(
i
.e., o
f
t
h
eor
d
er o
f
1–3 mg
/
cm
2
p
er
h
r
f
o
r
m
ost species). Most of this loss occurs via the respiratory system, despite the evolution of
m
echanical and physiological features to reduce such loss (Chapter 15). Water loss throug
h

th
e
i
nte
g
ument (sensu str
i
cto
)i
s
e
x
treme
ly
s
ligh
t, ma
i
n
ly b
ecause o
f
t
h
e
highly i
m
p
ermea
bl

e
epi
cut
i
c
l
ean
di
n
p
art
i
cu
l
ar t
h
e wax com
p
onents. Ear
ly
ex
p
er
i
ments
d
emonstrate
d
t
h

at
p
ermea
bili
ty o
f
t
h
e
i
ntegument
i
sre
l
at
i
ve
l
y
i
n
d
epen
d
ent o
f
temperature up to a certa
i
npo
i

nt
(
the transition temperature), above which it increases markedly. As a result of his studies o
n
both artificial and natural systems, Beament (1961) concluded that the initial impermeability
i
s related to the hi
g
hl
y
ordered wax monola
y
er whose molecules sit on the tanned cuticulin
e
nvelo
p
eatanan
g
le of about 2
5
◦
to t
h
e
p
er
p
en
di
cu

l
ar ax
i
s, w
i
t
h
t
h
e
i
r
p
o
l
ar en
d
s
f
ac
i
n
g
i
nwar
d
an
d
nonpo
l

ar en
d
s outwar
d
.Int
hi
s arrangement t
h
emo
l
ecu
l
es are c
l
ose
l
y pac
k
e
d
and held tightly together by van der Waals forces. As temperature increases, the molecules
g
ain kinetic energy, and eventually the bonds between them rupture. Spaces appear an
d
w
ater loss increases si
g
nificantl
y
. The nature of the wax and its transition tem

p
erature ca
n
b
e corre
l
ate
d
w
i
t
h
t
h
e norma
l
n
i
c
h
eo
f
t
h
e
i
nsect
.
Insects
f

rom
h
um
id
env
i
ronments or t
h
at
h
ave access to mo
i
sture
i
nt
h
e
i
r
di
et,
f
or exam
pl
e, a
phid
s, cater
pill
ars, an
dbl

oo
d
suc
ki
n
g
i
nsects, have “soft” waxes, with low transition temperatures. Forms from dry environment
s
o
r stages with water-conservation problems, for example, eggs and pupae, are covered wit
h
“
hard” wax, whose transition tem
p
erature is hi
g
h (in most s
p
ecies above the thermal deat
h
p
o
i
nt o
f
t
h
e
i

nsect)
.
M
ore recent stu
di
es
h
ave
q
uest
i
one
d
t
h
eva
lidi
t
y
o
f
Beament’s or
d
ere
d
mono
l
a
y
er

m
o
d
e
l
.Ev
id
ence aga
i
nst
i
t
i
nc
l
u
d
es t
h
eo
b
servat
i
on t
h
at
h
y
d
rocar

b
ons (non-po
l
ar mo
l
ecu
l
es
)
are the dominant component of wax, physicochemical analyses that indicate that th
e
li
p
ids have no
p
referred orientation, and mathematical calculations that show the abru
pt
p
ermea
bili
t
y
c
h
an
g
es at t
h
e so-ca
ll

e
d
trans
i
t
i
on
p
o
i
nt to
b
e art
if
actua
l
(B
l
om
q
u
i
st an
d
Dillwith, 1985).
S
ome
i
nsects t
h

at are norma
ll
y
f
oun
di
n extreme
l
y
d
ry
h
a
bi
tats an
d
may go
f
or
l
ong
periods without access to free water, for example,
Te
n
eb
r
io
m
olito
r

a
nd prepupae of fleas
,
368
CHAPTER
11
are able to take up water from an atmosphere in which the humidity is relatively high.
O
ri
g
inall
y
it was believed that u
p
take occurred across the bod
y
surface
p
erha
p
s via the
p
ore
c
ana
l
s. However,
i
t
h

as now
b
een
d
emonstrate
d
t
h
at u
p
ta
k
e occurs across t
h
ewa
ll
o
f
t
he
rectum (C
h
a
p
ter 18, Sect
i
on 4.1)
.
In many
f

res
h
water
i
nsects,
f
or examp
l
e, a
d
u
l
t Heteroptera an
d
Co
l
eoptera, t
h
e cut
i
c
l
e
is highly impermeable because of its wax monolayer and water gain is probably 4% or les
s
o
f the bod
y
wei
g

ht
p
er da
y
. In most a
q
uatic insects, however, the wax la
y
er is absent. Thus,
g
a
i
ns o
f
u
p
to 30% o
f
t
h
e
b
o
dy
we
igh
t
p
er
d

a
y
are ex
p
er
i
ence
d
,t
h
e excess water
b
e
i
n
g
remove
d
v
i
at
h
e excretor
y
s
y
stem (C
h
a
p

ter 18, Sect
i
on 4.2).
I
nsecticides.
E
conomic motives have stimulated an enormous interest in the perme
-
abilit
y
of the inte
g
ument to chemicals, es
p
eciall
y
insecticides and their solvents (Ebelin
g,
1
974). T
h
ou
gh
,
f
or t
h
e most
p
art, t

h
e cut
i
c
l
e acts as a
phy
s
i
ca
lb
arr
i
er to
d
ecrease t
h
e rat
e
of
entr
y
o
f
suc
h
mater
i
a
l

s, t
h
ere
i
sev
id
ence t
h
at
i
n some
i
nsects
i
tma
y
a
l
so
b
r
i
n
g
a
b
out
meta
b
o

li
c
d
egra
d
at
i
on o
f
certa
i
n compoun
d
s, an
d
consequent
l
yre
d
uct
i
on o
f
t
h
e
i
r potency.
It follows that increased resistance to a particular compound may result from changes in ei-
ther the structure or the metabolic

p
ro
p
erties of the inte
g
ument (see also Cha
p
ter 16, Section
5
.5). For most insects, the
p
rimar
y
barrier to the entrance of insecticides is the e
p
icuticular
w
ax, w
hi
c
hdi
sso
l
ves an
d
reta
i
ns t
h
ese

l
ar
g
e
ly lipid
-so
l
u
bl
e mater
i
a
l
s. For t
h
e same reason,
t
h
e cement
l
ayer a
l
so pro
b
a
bl
y prov
id
es some protect
i

on aga
i
nst penetrat
i
on. T
h
e procut
i-
c
le offers both lipid and aqueous pathways along which an insecticide may travel, but the
p
recise rate at which a com
p
ound moves de
p
ends on man
y
variables, es
p
eciall
y
thicknes
s
of
t
h
e cut
i
c
l

e,
p
resence or a
b
sence o
fp
ore cana
l
s, an
d
w
h
et
h
er t
h
e
l
atter are fi
ll
e
d
w
i
t
h
cy
to
pl
asm

i
c extens
i
ons or ot
h
er mater
i
a
l
.It
f
o
ll
ows t
h
at t
h
e rate o
fp
enetrat
i
on w
ill
var
y
accor
di
ng to t
h
e 1ocat

i
on o
f
an
i
nsect
i
c
id
eont
h
e
i
ntegument. However,
i
t
h
as a
l
so
b
een
noted that dissolution in the wax will facilitate lateral movement of the insecticides, perhaps
allowing them to reach the tracheal system and thus gain access. Thin, membranous cuticl
e
s
uc
h
as occurs
i

n
i
nterse
g
menta
l
re
gi
ons or covers tact
il
eorc
h
emosensor
yh
a
i
rs
g
enera
lly
p
rov
id
es
li
tt
l
e res
i
stance to

p
enetrat
i
on. T
h
e trac
h
ea
l
s
y
stem
i
s anot
h
er s
i
te o
f
entr
y
.T
he
extent to w
hi
c
h
tann
i
ng o

f
t
h
e procut
i
c
l
e occurs
i
sa
l
so re
l
ate
d
to penetrat
i
on rate. As t
h
e
c
hitin-protein micelles become more tightly packed and the cuticle partially dehydrated
,
p
ermeability decreases.
In addition, but obviousl
y
related to the
p
h

y
sical features of the cuticle, the
p
h
y
sico
-
ch
em
i
ca
l
nature o
f
an
i
nsect
i
c
id
e
i
san
i
m
p
ortant
f
actor
i

n
d
eterm
i
n
i
n
g
t
h
e rate o
f
entr
y
.
Espec
i
a
ll
ys
i
gn
i
ficant
i
st
h
e part
i
t

i
on coe
f
fic
i
ent (t
h
ere
l
at
i
ve so
l
u
bili
ty
i
no
il
an
di
n water)
o
f an insecticide or its solvent. In order to penetrate the epicuticular wax the material mus
t
be relatively lipid-soluble. However, in order to pass through the relatively polar procuti
-
c
le and, eventuall
y

, to leave the inte
g
ument to move toward its site of action, the material
must
b
e
p
art
i
a
lly
water-so
l
u
bl
e. T
h
us, correct
f
ormu
l
at
i
on o
f
an
i
nsect
i
c

id
a
l
so
l
ut
i
on
i
san
i
m
p
ortant cons
id
erat
i
on.
It s
h
ou
ld b
e apparent
f
rom t
h
ea
b
ove
di

scuss
i
on t
h
at
f
ew genera
li
zat
i
ons can
b
ema
d
e
.
A
t the present time, therefore, the suitability of an insecticide must be considered separatel
y
f
or each s
p
ecies. Because of the factors that affect the entr
y
of insecticides, a
g
reat differenc
e
usua
lly

ex
i
sts
b
etween “rea
l
tox
i
c
i
t
y
,” t
h
at
i
s, tox
i
c
i
t
y
at t
h
es
i
te o
f
act
i

on, an
d
“a
pp
aren
t
tox
i
c
i
t
y
,” t
h
e amount o
f
mater
i
a
l
t
h
at must
b
ea
ppli
e
d
to
pi

ca
lly
to
b
r
i
n
g
a
b
out
d
eat
h
o
f
t
he
i
nsect. T
h
ec
hi
e
ff
eature t
h
at re
l
ates t

h
etwo
i
so
b
v
i
ous
l
yt
h
e “penetrat
i
on ve
l
oc
i
ty,” t
h
at
i
s
,
the rate at which material passes through the cuticle. When the rate is high, the real and
a
pp
arent toxicit
y
values will be nearl
y

identical.
369
THE INTE
GU
MEN
T
4.3. Colo
r
As in other animals, the color of insects serves to conceal them from predators (some-
t
imes through mimicry), frighten or “warn” predators that potential prey is distasteful, or
facilitate intras
p
ecific and/or sexual reco
g
nition. It ma
y
be used also in thermore
g
ulation
.
T
h
eco
l
or o
f
an
i
nsect

g
enera
lly d
e
p
en
d
sont
h
e
i
nte
g
ument. Rare
ly
,an
i
nsect’s co
l
or ma
y
b
et
h
e resu
l
to
f pig
ments
i

nt
i
ssues or
h
emo
ly
m
ph b
e
l
ow t
h
e
i
nte
g
ument. For exam
pl
e, t
h
e
r
e
d
co
l
or o
f
Ch
ironomus

l
arvae
i
s cause
db
y
h
emog
l
o
bi
n
i
nso
l
ut
i
on
i
nt
h
e
h
emo
l
ymp
h.
I
ntegumental colors may be produced in two ways. Pigmentary colors are produced whe
n

p
i
g
ments in the inte
g
ument (usuall
y
the cuticle) absorb certain wavelen
g
ths of li
g
ht and
r
e
fl
ect ot
h
ers (Fuzeau-Bresc
h
, 1972). P
hy
s
i
ca
l
(structura
l
)co
l
ors resu

l
tw
h
en
ligh
twave
s
o
f
a certa
i
n
l
en
g
t
h
are re
fl
ecte
d
as a resu
l
to
f
t
h
e
phy
s

i
ca
lf
eatures o
f
t
h
e sur
f
ace o
f
t
he
i
ntegument.
Pigmentary colors result from the presence in molecules of particular bonds between
atoms. Especially important are double bonds such as
C
=
C
,
C
=
O,
C
=
N, and
N
=
N

whic
h
absorb
p
articular wavelen
g
ths of li
g
ht (Hackman, 1974; Ka
y
ser, 1985). The inte
g
umen
t
m
a
y
conta
i
navar
i
et
y
o
f pig
ment mo
l
ecu
l
es t

h
at
p
ro
d
uce c
h
aracter
i
st
i
cco
l
ors. Usua
lly
th
emo
l
ecu
l
e,
k
nown as a c
h
romop
h
ore,
i
s con
j

ugate
d
w
i
t
h
a prote
i
nto
f
ormac
h
romo
-
protein. The brown or black color of many insects results usually from melanin pigment.
Melanin is a molecule composed of polymerized indole or quinone rings. Typically, it
i
s located in the cuticle
,
but i
n
C
arausiu
s
it occurs in the e
p
idermis, where it is ca
p
a-
bl

eo
f
movement an
d
ma
yb
e concerne
d
w
i
t
h
t
h
ermore
g
u
l
at
i
on as we
ll
as concea
l
ment
.
Caroteno
id
s are common
pig

ments o
f phy
to
ph
a
g
ous
i
nsects. T
h
e
y
are ac
q
u
i
re
d
t
h
rou
gh
feeding as insects are unable to synthesize them. Carotenoids generally produce yellow,
orange, and red colors, and, in combination with a blue pigment, mesobiliverdin, produce
g
reen. Exam
p
les of the use of carotenoids include the
y
ellow color of matur

e
Schistocerc
a
a
n
d
t
h
ere
d
co
l
or o
f
P
yrrhocoris an
d
Coccinella. Pter
idi
nes, w
hi
c
h
are
p
ur
i
ne
d
er

i
vat
i
ves,
are common
pig
ments o
f
Le
pid
o
p
tera, H
y
meno
p
tera, an
d
t
h
e
h
em
ip
teran
Dy
s
d
ercu
s

,
an
d
pro
d
uce ye
ll
ow , w
hi
te, an
d
re
d
co
l
ors. Ommoc
h
romes, w
hi
c
h
are
d
er
i
vat
i
ves o
f
trypto-

phan, an amino acid, are an important group of pigments that produce yellow, red, an
d
b
rown colors. Exam
p
les of colors resultin
g
from ommochromes are the
p
ink of immature
a
d
u
lt
S
chistocerca
,
t
h
ere
d
o
f
O
d
onata, an
d
t
h
ere

d
san
db
rowns o
f
n
y
m
ph
a
lid b
utter-
fli
es. In some
i
nsects t
h
ec
h
aracter
i
st
i
cre
d
or
y
e
ll
ow

b
o
dy
co
l
or
i
st
h
e resu
l
to
ffl
avones
or
i
g
i
na
ll
y present
i
nt
h
e
f
oo
d
p
l

ant. Ur
i
cac
id
,t
h
ema
j
or n
i
trogenous excretory pro
d
uc
t
of insects (Chapter 18, Section 3.1), is deposited in specific regions of the epidermis
i
n some insects. For example, in
D
ysdercu
s
it is responsible for the white areas of the
i
nte
g
ument.
P
hy
s
i
ca

l
co
l
ors are
p
ro
d
uce
dby
scatter
i
n
g
,
i
nter
f
erence, or
diff
ract
i
on o
f ligh
tt
h
ou
gh
th
e
l

atter
i
s extreme
l
y rare. Most w
hi
te,
bl
ue, an
di
r
id
escent co
l
ors are pro
d
uce
d
us
i
n
g
t
he first two methods. White results from the scattering of light by an uneven surface or
b
y granules that occur below the surface. When the irregularities are large relative to th
e
wav
e
len

g
th of li
g
ht, all colors are reflected e
q
uall
y
, and white li
g
ht results. An interference
co
l
or
i
s
p
ro
d
uce
dbyl
am
i
nate
d
structures w
h
en t
h
e
di

stance
b
etween success
i
ve
l
am
i
nae
i
ss
i
m
il
ar to t
h
ewave
l
en
g
t
h
o
f ligh
tt
h
at
p
ro
d

uces t
h
at
p
art
i
cu
l
ar co
l
or. As
ligh
t str
ik
es
t
he laminae light waves of the “correct” length will be reflected by successive surfaces, an
d
t
he color they produce will therefore be reinforced. Light waves of different lengths will be
out of
p
hase. Chan
g
in
g
the an
g
le at which li
g

ht strikes the surface (or e
q
uall
y
the an
g
le at
whi
c
h
t
h
e sur
f
ace
i
sv
i
ewe
d
)
i
se
q
u
i
va
l
ent to a
l

ter
i
n
g
t
h
e
di
stance
b
etween
l
am
i
nae. In turn
,
3
7
0
CHAPTER
11
this will alter the wavelength that is reinforced and color that is produced. This change o
f
c
olor in relation to the an
g
le of viewin
g
is termed iridescence. Iridescent colors are commo
n

i
n man
y
Co
l
eo
p
tera an
d
Le
pid
o
p
tera.
4
.4.
O
ther Funct
i
on
s
T
he cuticular waxes ma
y
have im
p
ortant roles in
p
reventin
g

the entr
y
of microor
g
anism
s
an
di
nc
h
em
i
ca
l
commun
i
cat
i
on (
i
.e., t
h
e
y
serve as sem
i
oc
h
em
i

ca
l
s). It
h
as
b
een su
gg
este
d
t
h
at t
h
e waxes ma
yp
revent a
dh
es
i
on o
f
m
i
croor
g
an
i
sms or ma
yb

e tox
i
ctot
h
em. Cut
i
cu
l
a
r
h
y
d
rocar
b
ons are a
l
so
k
nown to serve as contact sex p
h
eromones,
f
or examp
l
e,
i
n
f
ema

le
D
iptera an
d
B
l
atte
ll
a
,
attracting or inducing copulatory behavior in males, or serving as
an aphrodisiac to keep the male in position until insemination has occurred (Scha
l
et al.
,
1
998). In termites, the cuticular h
y
drocarbon blend is hi
g
hl
y
s
p
ecific and serves as a s
p
ecies
-
an
d/

or caste-reco
g
n
i
t
i
on
ph
eromone. (See a
l
so C
h
a
p
ter 13, Sect
i
on 4.1.2.) Interest
i
n
gly
,
some
b
eet
l
es t
h
at
li
ve

i
n term
i
te co
l
on
i
es pro
d
uce t
h
e same
h
y
d
rocar
b
on profi
l
east
he
host, enabling them to remain unmolested in the nest. The species-specific nature of the
l
ipids has been turned to advantage by some parasitic Hymenoptera who use these chemical
c
ues (known as kairomones [Cha
p
ter 13, Section 4.2.) to locate their host (Blom
q
uist an

d
D
illwith, 1985)
.
5.
S
ummary
Th
e
i
nte
g
ument
i
sa
l
a
y
ere
d
structure t
h
at com
p
r
i
ses a
b
asa
ll

am
i
na, e
pid
erm
i
s,
p
ro
-
c
ut
i
c
l
e, ep
i
cut
i
c
l
e, an
d
cut
i
cu
li
nenve
l
ope. T

h
e
b
asa
ll
am
i
na conta
i
ns car
b
o
h
y
d
rate an
d
c
ollagenlike material and is mainly a product of the epidermal cells. The epidermis is
mostly a one-cell-thick layer of uniform cells, though the cells can differentiate to form der-
ma
lgl
an
d
s, oenoc
y
tes, or sensor
y
structures. T
h

e
p
rocut
i
c
l
e
i
nc
l
u
d
es an
i
nner en
d
ocut
i
c
l
e
an
d
an outer exocut
i
c
l
e,
b
ot

h
o
f
w
hi
c
h
conta
i
nam
i
xture o
f
c
hi
t
i
n(a
p
o
ly
mer
i
ze
d
n
i
tro
g
e

-
nous po
l
ysacc
h
ar
id
eo
f
fi
b
rous
f
orm) an
d
prote
i
n. T
h
een
d
ocut
i
c
l
e
i
s
l
am

i
nar,
fl
ex
ibl
e, an
d
c
apable of being digested by molting fluid; the exocuticle is hard, inflexible, and chemi-
c
ally inert as a result of tanning, the covalent linking of proteins via quinones. Exocuticle
i
sa
b
sent
f
rom areas o
f
t
h
e
b
o
dy
w
h
ere
fl
ex
ibili

t
yi
sre
q
u
i
re
d
,
f
or exam
pl
e, at
j
o
i
nts an
d
i
nterse
g
menta
l
mem
b
ranes, an
di
sver
y
t

hi
n
i
nso
f
t-
b
o
di
e
dl
arvae. T
h
ee
pi
cut
i
c
l
e
i
nc
l
u
d
es
a
tanne
d
prote

i
n
l
ayer, t
h
e prote
i
naceous ep
i
cut
i
c
l
e, w
hi
c
hli
es
i
ns
id
et
h
e cut
i
cu
li
nenve
l
ope,

as well as in most terrestrial species wax and cement which sit outside the envelope. Wax i
s
p
roduced by oenocytes, cement by dermal glands. The cuticulin envelope, a very thin layer
o
f unknown com
p
osition, is the sin
g
le most im
p
ortant com
p
onent of the cuticle
.
Cut
i
c
l
e
f
ormat
i
on
i
s a success
i
on o
f
s

y
nt
h
eses
by
t
h
ee
pid
erma
l
ce
ll
s, w
i
t
h
t
h
e oenoc
y
tes
an
dd
erma
lgl
an
d
sa
ddi

n
g
t
h
e
i
r secret
i
ons at t
h
ea
pp
ro
p
r
i
ate t
i
me. A
f
ter a
p
o
ly
s
i
s, ec
dy
s
i

a
l
droplets are released and, after formation of the new cuticulin envelope, the enzymes in th
e
droplets are activated to digest almost all of the old endocuticle. In new procuticle formation
,
much of the raw material from the di
g
ested endocuticle is reused. Wax de
p
osition occurs
j
us
t
p
r
i
or to ec
dy
s
i
san
d
,
lik
een
d
ocut
i
c

l
e
p
ro
d
uct
i
on, cont
i
nues
d
ur
i
n
gi
ntermo
l
t. T
h
e cement
l
a
y
er
i
s
l
a
id d
own a

f
ter ec
dy
s
i
s. Tann
i
n
g
o
f
t
h
e outer
p
rocut
i
c
l
e, to
f
orm t
h
e exocut
i
c
l
e, a
l
so

ta
k
es p
l
ace at t
hi
st
i
me.
T
he strength and hardness of the cuticle enable this layer to serve both as an exoskeleton
and in the
p
rotection of the insect a
g
ainst
p
h
y
sical dama
g
e and entr
y
of
p
atho
g
ens. Th
e
3

7
1
THE INTE
GU
MEN
T
wa
x layer is important in reducing water loss (entry) in terrestrial (freshwater) insects, is a
b
arrier to insecticides, and, for some insects, contains
p
heromones. Color is also a function
o
f
t
h
e
i
nte
g
ument,
b
e
i
n
gp
ro
d
uce
d

e
i
t
h
er
by pig
ments
i
nt
h
ee
pid
erm
i
s or, more
f
re
q
uent
ly
,
as a resu
l
to
f
t
h
e structure o
f
t

h
e cut
i
c
l
e
.
6
. Literatur
e
G
enera
l
rev
i
ews o
fi
nte
g
ument structure an
df
unct
i
on are
gi
ven
by
Loc
k
e (1974),

N
eville (197
5
), Hepburn (1976, 198
5
), and Bereiter-Hahn et a
l.
(
1984). Spec
i
a
li
ze
d
c
h
apter
s
i
nclude those by Ebeling (1974) and Blomquist and Dillwith (198
5
) [permeability of cuticle,
e
s
p
eciall
y
the wax la
y
er], Hackman (1974) [chemistr

y
of cuticle], Andersen (1985) an
d
Ho
p
kins and Kramer (1992) [tannin
g
], and Ka
y
ser (1985) [
p
i
g
ments], and b
y
authors i
n
th
e treat
i
se e
di
te
dby
B
i
nn
i
n
g

ton an
d
Retna
k
aran (1991)
.
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ompre
h
ensive Insect P
h
ysio
l
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h
emistr
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d
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h
armaco
l
og
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i
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h
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ysio
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armaco
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i
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ocke, M., 1969, The ultrastructure of the oenocytes in the molt/intermolt cycle of an insect
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ormat
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i
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ocke, M., 1991, Insect epidermal cells, in
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