Entomology 3rd edition - C.Gillott - Chapter 18 ppt

1
8
N
itrogenous Excretion an
d
Sa
l
tan
d
W
ater Ba
l
ance
1
. Introduct
i
o
n
E
nzymatically controlled reactions occur at the optimum rate within a narrow range of
physical conditions. Especially important are the pH and ionic content of the cell fluid, a
s
t
hese factors readil
y
affect the active site on an enz
y
me. As the conditions existin
g
within
ce

ll
san
d
t
i
ssues are necessar
ily d
e
p
en
d
ent on t
h
e nature o
f
t
h
e
fl
u
id
t
h
at
b
at
h
es t
h
em—

i
n
i
nsects, t
h
e
h
emo
l
ymp
h
—
i
t
i
st
h
eregu
l
at
i
on o
f
t
hi
s
fl
u
id
t

h
at
i
s
i
mportant. By regu
l
at
i
o
n
i
s meant the removal of unwanted materials and the retention of those that are useful
,
t
o maintain as nearly as possible the best cellular environment. Regulation is a functio
n
of the excretor
y
s
y
stem and is of
g
reat im
p
ortance in insects because the
y
occu
py
such

var
i
e
dh
a
bi
tats an
d
,t
h
ere
f
ore,
h
ave
diff
erent re
g
u
l
ator
y
re
q
u
i
rements. Terrestr
i
a
li

nsects
l
os
e
w
ater
b
y evaporat
i
on t
h
roug
h
t
h
e
i
ntegument an
d
resp
i
ratory sur
f
aces an
di
nt
h
e process o
f
n

itrogenous waste removal. Brackish-water and saltwater forms also lose water as a result of
osmosis across the integument; in addition, they gain salts from the external medium. Insect
s
i
nhabitin
g
fresh water
g
ain water from and lose salts to the environment. The
p
roblem o
f
osmore
g
u
l
at
i
on
i
s com
pli
cate
dby
an
i
nsect’s nee
d
to remove n
i

tro
g
enous waste
p
ro
d
ucts
o
f
meta
b
o
li
sm, w
hi
c
hi
n some
i
nstances are ver
y
tox
i
c. T
hi
s remova
l
uses
b
ot

h
sa
l
ts an
d
w
ater, one or both of which must be recovered later from the urine.
2
. Excretor
ySy
stem
s
2
.
1
. Malp
i
gh
i
an Tubules—Rectu
m
The Malpighian tubules and rectum, functioning as a unit, form the major excretor
y
s
y
stem in most insects. Details of the rectum are
g
iven in Cha
p
ter 16, Section 3.4, and onl

y
th
e structure o
f
t
h
etu
b
u
l
es
i
s
d
escr
ib
e
dh
ere
.
T
h
e
bli
n
dly
en
di
n
g

tu
b
u
l
es, w
hi
c
h
usua
lly li
e
f
ree
ly i
nt
h
e
h
emocoe
l
,o
p
en
i
nto t
h
e
alimentary canal at the junction of the midgut and hindgut (Figure 18.1A). Typically they
e
nter the gut individually but may fuse first to form a common sac or ureter that leads

i
nto the
g
ut. Their number varies from two to several hundred and does not a
pp
ear to be
5
37
53
8
C
HAPTER
18
F
IGURE 18.1
.
(A) Excretory system o
f
Rhodnius. Only one Malpighian tubule is drawn in full; (B) junction of
p
rox
i
ma
l
an
ddi
sta
l
se
g

ments o
f
aMa
lpighi
an tu
b
u
l
eo
f
R
h
o
d
nius
.
P
art o
f
t
h
etu
b
u
l
e
h
as
b
een cut awa

y
to s
h
ow t
he
c
ellular differentiation; (C, D) sections of the wall of the distal and
p
roximal se
g
ments, res
p
ectivel
y
, of a tubule;
a
n
d
(E) t
i
po
f
Ma
l
p
i
g
hi
an tu
b

u
l
eo
f
A
pi
s
t
os
h
ow trac
h
eo
l
es an
d
sp
i
ra
l
musc
l
es. [A, B, E, a
f
ter V. B. W
i
gg
l
eswort
h

,
196
5,
Th
e Princip
l
es o
f
Insect P
hy
sio
l
og
y
,6
t
h
e
d
., Met
h
uen an
d
Co. B
yp
erm
i
ss
i
on o

f
t
h
e aut
h
or.C,D,
f
ro
m
V.
B. Wi
gg
lesworth and M. M. Salt
p
eter, 1962, Histolo
gy
of the Mal
p
i
g
hian tubules in Rhodnius
p
rolixus
S
tal
.
(Hem
i
ptera), J. Insect Physiol.
8

:299–307. By perm
i
ss
i
on o
f
Pergamon Press Lt
d
.
]
c
losely related to either the phylogenetic position or the excretory problems of an insect
.
M
alpighian tubules are absent in Collembola, some Diplura, and aphids; in other Diplura,
P
rotura, and Stre
p
si
p
tera there are
p
a
p
illae at the
j
unction of the mid
g
ut and hind
g

ut.
W
i
t
h
t
h
etu
b
u
l
es are assoc
i
ate
d
trac
h
eo
l
es an
d
, usua
lly
, musc
l
es (F
ig
ure 18.1E). T
h
e

l
atter
ta
k
et
h
e
f
orm o
f
a cont
i
nuous s
h
eat
h
,
h
e
li
ca
l
str
i
ps, or c
i
rcu
l
ar
b

an
d
san
d
are s
i
tuate
d
o
utside the basal lamina. They enable the tubules to writhe, which ensures that differen
t
p
arts of the hemolymph are exposed to the tubules and assists in the flow of fluid along th
e
tubules.
Atu
b
u
l
e
i
sma
d
eu
p
o
f
as
i
n

gl
e
l
a
y
er o
f
e
pi
t
h
e
li
a
l
ce
ll
s, s
i
tuate
d
on t
h
e
i
nner s
id
eo
fa
b

asa
ll
am
i
na (F
ig
ure 18.1B–D). In man
y
s
p
ec
i
es w
h
ere t
h
etu
b
u
l
es
h
ave on
ly
a secretor
y
f
unction (Section 3.2) the histology of the tubules is constant throughout their length and
basically resembles that of the distal part of the tubule of R
h

o
d
nius
(
Figure 18.1C). The
inner (a
p
ical) surface of the cells takes the form of a brush border (microvilli). The oute
r
(
b
asa
l
) sur
f
ace
i
sa
l
so extens
i
ve
ly f
o
ld
e
d
. Bot
h
o

f
t
h
ese
f
eatures are t
ypi
ca
l
o
f
ce
ll
s
i
nvo
l
ve
d
i
nt
h
e trans
p
ort o
f
mater
i
a
l

san
d
serve to
i
ncrease enormous
ly
t
h
e sur
f
ace area across w
hi
c
h
transport can occur. Numerous m
i
toc
h
on
d
r
i
a occur, espec
i
a
ll
ya
dj
acent to or w
i

t
hi
nt
he
f
olded areas, to supply the energy requirements for active transport of certain ions acros
s
the tubule wall. In many species various types of intracellular crystals occur which are
53
9
N
ITR
O
GEN
O
U
S
EX
C
RETION
A
ND
S
ALT AND
WA
TER B
A
L
A
NC

E
presumed to represent a form of storage excretion (Section 3.3). Adjacent cells are closely
a
pp
osed near their a
p
ical and basal mar
g
ins, thou
g
h not necessaril
y
elsewhere.
I
n some
i
nsects (e.
g
., Rh
o
dniu
s
), two
di
st
i
nct zones can
b
e seen
i

nt
h
eMa
lpighi
an
t
u
b
u
l
e(F
ig
ure 18.1C, D). In t
h
e
di
sta
l
(secretor
y
) zone t
h
ece
ll
s
p
ossess
l
ar
g

e num
b
ers o
f
c
l
ose
l
y pac
k
e
d
m
i
crov
illi
,
b
ut very
f
ew
i
n
f
o
ldi
ngs o
f
t
h

e
b
asa
l
sur
f
ace. M
i
toc
h
on
d
r
i
aar
e
located near or within the microvilli. In the proximal (absorptive) part of the tubule the
cells
p
ossess fewer microvilli,
y
et show more extensive inva
g
ination of the basal surface
.
T
h
em
i
toc

h
on
d
r
i
a are corres
p
on
di
n
gly
more even
ly di
str
ib
ute
d
.Int
h
e
fli
e
s
Dacu
s
an
d
Droso
p
hil

a
,
w
h
ere
p
a
i
rs o
f
Ma
lpighi
an tu
b
u
l
es un
i
te to
f
orm a ureter
p
r
i
or to
j
o
i
n
i

n
g
t
he
g
ut, t
h
eu
l
trastructure o
f
t
h
e ureter resem
bl
es t
h
at o
f
t
h
e prox
i
ma
l
part o
f
t
he
R

hod
niu
s
t
ubule, suggesting that the ureter may be a site of resorption of materials from the urine
.
Y
e
t
o
ther species have even more complex Malpighian tubules in which up to four dis-
ti
nct re
gi
ons ma
yb
e
di
st
i
n
g
u
i
s
h
e
d
on
hi

sto
l
o
gi
ca
l
or u
l
trastructura
lg
roun
d
s. On t
h
e
b
as
i
s
o
f
t
h
e structura
lf
eatures o
f
t
h
e

i
rce
ll
s, t
h
ese re
gi
ons
h
ave
b
een
d
es
ig
nate
d
as secretor
y
or
a
b
sorpt
i
ve, t
h
oug
hi
t must
b

e emp
h
as
i
ze
d
t
h
at p
h
ys
i
o
l
og
i
ca
l
ev
id
ence
f
or t
h
ese propose
d
functions is largely lacking. For a survey of insects whose tubules show regional differen
-
t
iation and a discussion of tubule function in such species, see Jarial and Scudder (1970).

Acr
yp
tone
p
hridial arran
g
ement of Mal
p
i
g
hian tubules is found in larvae and adult
s
o
f
man
y
Co
l
eo
p
tera, some
l
arva
l
H
y
meno
p
tera an
d

Neuro
p
tera, an
d
near
ly
a
ll l
arva
l
L
ep
id
optera (F
i
gure 18.2). Here t
h
e
di
sta
l
port
i
on o
f
t
h
eMa
l
p

i
g
hi
an tu
b
u
l
es
i
sc
l
ose
l
y
apposed to the surface of the rectum and enclosed within a perinephric membrane. The sys-
t
em is particularly well developed in insects living in very dry habitats, and in such species
i
ts function is to im
p
rove water resor
p
tion from the material in the rectum (Section 4.1)
.
2
.2. Other Excretor
y
Structures
Even in insects that use the rectum as the primary site of osmoregulation, the ileum
m

a
y
nonetheless be a site for water or ion resor
p
tion. In other s
p
ecies where the rectum i
s
u
n
i
m
p
ortant
i
n osmore
g
u
l
at
i
on, serv
i
n
g
on
ly
to store ur
i
ne an

df
eces
p
r
i
or to ex
p
u
l
s
i
on, t
h
e
il
eum o
f
ten ta
k
es on t
hi
sro
l
e
.
I
na
f
ew
i

nsects t
h
e
l
a
bi
a
l
g
l
an
d
s may
f
unct
i
on as excretory organs. In apterygotes t
h
a
t
lack Malpighian tubules the glands can accumulate and eliminate dyes such as ammonia
carmine and indigo carmine from the hemolymph, but there is no evidence that they can
d
eal similarl
y
with nitro
g
enous or other wastes. The labial
g
lands of saturniid moths excret

e
co
pi
ous amounts o
ffl
u
id j
ust
p
r
i
or to emer
g
ence
f
rom t
h
e cocoon, an
di
tma
y
we
ll be
th
at t
h
epr
i
mary
f

unct
i
on o
f
t
h
eg
l
an
d
s
i
store
d
uce
h
emo
l
ymp
h
vo
l
ume an
dh
ence
b
o
d
y
w

eight, which, in such large flying insects, needs to be kept as low as possible. The midgu
t
of silkmoth larvae actively removes potassium from the hemolymph, thus protecting the
t
issues from the ver
y
hi
g
h concentration of
p
otassium ions
p
resent in the leaves eaten b
y
th
ese
i
nsects
.
I
na
f
ew
i
nsects
i
ta
pp
ears t
h

at t
h
eMa
lpighi
an tu
b
u
l
es, t
h
ou
gh p
resent,
pl
a
y
no
p
art
i
n nitrogenous excretion. In Peri
pl
aneta americana
,
for example, uric acid is not found i
n
t
he tubules but does occur in small amounts in the hindgut, which may excrete it directly
from the hemol
y

m
p
h. In
P.
a
mericana much uric acid is stored in urate cells in the fat bod
y
,
a
n
d
t
h
ema
j
or
f
orm o
f
excrete
d
n
i
tro
g
en
i
nt
hi
ss

p
ec
i
es
i
s ammon
i
a. How t
hi
s reac
h
es t
h
e
hi
n
dg
ut
l
umen
i
n
P.
am
e
r
i
can
a
i

s unc
l
ear. However,
i
nt
h
e
fl
es
hfly
S
arcopha
g
a bullat
a
,
ammon
i
a, t
h
epr
i
mary excretory pro
d
uct,
i
s act
i
ve
l

y secrete
d
as ammon
i
um
i
ons
i
nto t
h
e
lumen across the anterior hindgut wall.
5
4
0
C
HAPTER
18
F
I
GU
RE 18
.
2
.
Cr
yp
tone
ph
r

idi
a
l
arran
g
ement o
f
Ma
lpighi
an tu
b
u
l
es
i
n Tene
b
rio
l
arva. (A) Genera
l
a
pp
earance.
N
ote that only three of the six tubules are drawn fully and that in reality the tubules are much more convolute
d
an
dh
ave more

b
oursou
fl
ures t
h
an are s
h
own; (B) cross sect
i
on t
h
roug
h
poster
i
or reg
i
on o
f
cryptonep
h
r
idi
a
l
sy
stem; (C)
d
eta
il

so
f
a
l
e
p
to
ph
ra
g
ma; an
d
(D)
di
a
g
ram
ill
ustrat
i
n
gp
ro
p
ose
d
mo
d
eo
f

o
p
erat
i
on o
f
s
y
stem.
Solid arrows indicate movements of potassium, hollow arrows indicate movements of water. Numbers indicate
o
smot
i
c concentrat
i
on (measure
d
as
f
reez
i
ng-po
i
nt
d
epress
i
on) o
ffl
u

id
s
i
n
diff
erent compartments. [A
f
ter A. V.
G
r
i
mstone, A. M. Mu
lli
n
g
er, an
d
J. A. Ramsa
y
,19
6
8, Furt
h
er stu
di
es on t
h
e recta
l
com

pl
ex o
f
t
h
e mea
l
wor
m
Tenebri
o
m
o
lit
o
r
L
. (Coleoptera, Tenebrionidae)
,
P
hilos. Trans. R.
S
oc. Lond.
S
er.
B
25
3
:343–382. By permissio
n

of
t
h
eRoya
l
Soc
i
ety, Lon
d
on, an
d
Pro
f
essor J. A. Ramsay.]
54
1
N
ITR
O
GEN
O
U
S
EXCRETION
A
ND
S
ALT AND
WA
TER B

A
L
A
NC
E
I
n males of some species of cockroaches, for example, B
l
atte
ll
a germanic
a
,a
consi
d
-
e
rable amount of uric acid (as much as 5% of the live wei
g
ht of the insect) is found in the
u
tr
i
cu
li
ma
j
ores (
p
art o

f
t
h
e accessor
y
re
p
ro
d
uct
i
ve
gl
an
d
com
pl
ex). T
h
eur
i
cac
id b
ecomes
part o
f
t
h
ewa
ll

o
f
t
h
e spermatop
h
ore an
di
s,
i
n a sense, “excrete
d
”
d
ur
i
ng copu
l
at
i
on.
3
. Nitrogenous Excretio
n
3
.1. The Nature of Nitrogenous Wastes
I
nn
i
trogenous wastes structura

l
comp
l
ex
i
ty, tox
i
c
i
ty, an
d
so
l
u
bili
ty go
h
an
di
n
h
an
d
.
The simplest form of waste (ammonia) is highly toxic and very water-soluble. It contains a
h
i
g
h
p

ro
p
ortion of h
y
dro
g
en that can be used in
p
roduction of water. It is
g
enerall
y
found a
s
th
ema
j
or excretor
yp
ro
d
uct, t
h
ere
f
ore, on
ly i
nt
h
ose

i
nsects t
h
at
h
ave ava
il
a
bl
e
l
ar
g
e amount
s
o
f
water,
f
or exam
pl
e,
l
arvae an
d
a
d
u
l
ts o

ff
res
h
water s
p
ec
i
es. Nonet
h
e
l
ess, exce
p
t
i
ons are
k
nown, t
h
e
b
est examp
l
es
b
e
i
ng t
h
e

l
arvae o
f
meat-eat
i
ng
fli
es an
d
P
.
a
m
e
r
i
cana un
d
e
r
certain dietary regimes. Generally, however, in insects, as in other terrestrial organisms
,
w
ater must be conserved, and more com
p
lex nitro
g
enous wastes are
p
roduced, which are

b
ot
hl
ess tox
i
can
dl
ess so
l
u
bl
e. In t
h
ee
gg
an
dp
u
p
a
l
sta
g
et
h
e
p
ro
bl
em

i
s accentuate
d
b
ecause water
l
ost cannot
b
ere
pl
ace
d
,an
d
n
i
tro
g
enous wastes must rema
i
n
i
nt
h
e
b
o
dy
i
nt

h
ea
b
sence o
f
a
f
unct
i
ona
l
excretory system. Most
i
nsects, t
h
en, excrete t
h
e
i
r wast
e
n
itrogen as uric acid. This is only slightly water-soluble, relatively non-toxic, and contains
a
smaller proportion of hydrogen compared with ammonia
.
However, ur
i
cac
id i

s not t
h
eon
ly f
orm o
f
n
i
tro
g
enous waste. Usua
lly
traces o
f
ot
h
e
r
m
ater
i
a
l
s (es
p
ec
i
a
lly
t

h
ere
l
ate
d
com
p
oun
d
sa
ll
anto
i
nan
d
a
ll
anto
i
cac
id
) can
b
e
d
etecte
d
,
an
di

n many spec
i
es one o
f
t
h
ese
h
as
b
ecome t
h
e pre
d
om
i
nant excretory pro
d
uct (Burse
ll
,
1967). Urea is rarely a major constituent of insect urine, usually representing less than 10%
of the nitrogen excreted. Traces of amino acids can be found in the excreta of many insects
,
but
t
h
e
i
r

p
resence s
h
ou
ld b
ere
g
ar
d
e
d
as acc
id
enta
ll
oss rat
h
er t
h
an
d
e
lib
erate excret
i
o
n
by
an
i

nsect (Burse
ll
,19
6
7). On
ly
occas
i
ona
lly h
as t
h
e excret
i
on o
fp
art
i
cu
l
ar am
i
no ac
id
s
b
een aut
h
ent
i

cate
d
;
f
or examp
l
e, t
h
ec
l
ot
h
es mot
h
Tine
o
l
a
a
n
d
t
h
e carpet
b
eet
le
A
tta
g

enus
e
xcrete large amounts of the sulfur-containing amino acid cystine. Although in tsetse flies
u
ric acid is the primary excretory product, two amino acids, arginine and histidine, are
i
m
p
ortant com
p
onents of the urine. These make u
p
about 10% of the
p
rotein amino acids
i
n
h
uman-
bl
oo
d
;
b
ecause t
h
e
i
rn
i

tro
g
en content
i
s
high
,
i
t
i
s
p
ro
b
a
bly
uneconom
i
ca
l
t
o
d
egra
d
et
h
em, an
d
t

h
ey are t
h
ere
f
ore excrete
d
unc
h
ange
d
(Burse
ll
,19
6
7). T
h
eam
i
no ac
ids
voided in honeydew by plant-sucking Hemiptera must be considered as largely fecal and not
m
etabolic waste products. Because of the large amount of water taken in by aphids, it has
b
een su
gg
ested that the
y
mi

g
ht
p
roduce ammonia as their nitro
g
enous waste. Indeed, uri
c
ac
id,
a
ll
anto
i
n
,
an
d
a
ll
anto
i
cac
id
cannot
b
e
d
etecte
di
nt

h
e
i
r excreta. However
,
ammon
i
a
m
akes u
p
onl
y
0.
5
% of the total nitro
g
en excreted, which has led to the su
gg
estion that it
i
s used (and detoxified) by symbiotic bacteria in mycetomes (Chapter 16, Section
5
.1.2)
.
Table 18.1 contains selected examples to show the variety of nitrogenous wastes produced
by
insects
.
As can

b
e seen
i
nF
ig
ure 18.3, ur
i
cac
id
an
d
t
h
eot
h
er n
i
tro
g
enous waste
p
ro
d
uct
s
are
d
er
i
ve

df
rom two sources, nuc
l
e
i
cac
id
san
dp
rote
i
ns. De
g
ra
d
at
i
on o
f
nuc
l
e
i
cac
id
s
is
o
f
m

i
nor
i
mportance; most n
i
trogenous waste comes
f
rom prote
i
n
b
rea
kd
own
f
o
ll
owe
d
b
y synthesis of hypoxanthine from amino acids. The biochemical reactions that lead t
o
s
y
nthesis of this
p
urine a
pp
ear to be similar to those found in other uric acid-excretin
g

or
g
an
i
sms (Burse
ll
,19
6
7; Barrett an
d
Fr
i
en
d
, 1970)
.
5
42
C
HAPTER
18
T
ABLE
1
8
.1.
N
itro
g
enous Excretor

y
Products of Various lnsect
s
a
,
b
U
ric acid Allantoin Allantoic acid
U
rea Ammonia Amino acid
s
Od
onat
a
Aeshna c
y
ane
a
(
larva
)
0.08 —
0.00
—1
.00 —
Dictyoptera/Phasmid
a
Perip
l
aneta americana

1
.
00 0
.
00 0
.
00
—
—
—
Bl
atta orienta
l
is 0.64 0.64 1.00 —
—
—
Di
x
ipp
us morosu
s
0.6
9
1.00 0.44 —
—
—
Hem
i
ptera
Dy

s
d
ercus
f
asciatu
s
0.00 1.00 0.00 0.2
6
— 0.2
4
R
hodnius
p
rolixu
s
1.00 —
— 0.33
— Trace
Coleoptera
M
e
l
o
l
ont
h
avu
lg
ari
s

1
.
00 0
.
00 0
.
00
—
—
—
Attagenus piceu
s
0.7
2
—
—
1
.00 0.57 0.50
Dipter
a
L
uci
l
ia sericata
1
.
00 0
.
30
—

—
0
.
30
—
L
uci
l
ia sericata (
p
u
p
a) 1.00 0.00 — — 0.1
5—
L
ucilia
s
ericata
(
larva
)
0.05 0.0
2
——1
.00 —
L
ep
id
opter
a

Pieris
b
rassica
e
1
.00 0.04 0.01 —
—
—
P
ieri
s
bra
ss
ica
e
(p
u
p
a) 1.00 0.03 0.0
5
——
—
P
ieri
s
bra
ss
ica
e
(

larva) 0.28 0.16 1.00 — —
—
a
From Bursell
(
1967
)
, after various authors.
b
The
q
uantit
y
of nitro
g
en excreted in the different
p
roducts is ex
p
ressed as a
p
ro
p
ortion of the nitro
g
en in the
p
redominant end
p
roduct

.
F
IGURE 18.
3.
M
eta
b
o
li
c
i
nterre
l
at
i
ons
hi
ps o
f
n
i
trogenous wastes. [A
f
ter E. Burse
ll
.19
6
7. T
h
e excret

i
on o
f
n
i
tro
g
en
i
n
i
nsects
.
A
d
v. Insect P
hy
sio
l
.
4
:33–
6
7. B
yp
erm
i
ss
i
on o

f
Aca
d
em
i
c Press Lt
d
.an
d
t
h
e aut
h
or.]
54
3
N
ITR
O
GEN
O
U
S
EXCRETION
A
ND
S
ALT AND
WA
TER BALANC

E
I
n addition to the enzymes for uric acid synthesis there are also uricolytic enzymes tha
t
catal
y
ze de
g
radation of this molecule in man
y
insects (Fi
g
ure 18.3). Uricase has a wide
di
str
ib
ut
i
on w
i
t
hi
nt
h
e Insecta. Act
i
ve
p
re
p

arat
i
ons o
f
a
ll
anto
i
nase
h
ave
b
een o
b
ta
i
ne
df
ro
m
m
an
y
s
p
ec
i
es,
b
ut t

h
e
di
str
ib
ut
i
on o
f
t
hi
s enz
y
me a
pp
ears to
b
e rat
h
er restr
i
cte
d
com
p
are
d
wi
t
h

ur
i
case. A
l
t
h
oug
h
t
h
ere are reports t
h
at
i
n
di
cate t
h
e occurrence o
f
a
ll
anto
i
case an
d
u
rease in tissue extracts from a few insects, their presence should not be regarded as havin
g
b

een established une
q
uivocall
y
. In other words, when urea and ammonia are
p
roduced i
n
s
ig
n
i
ficant amounts, t
h
e
y
are
p
ro
b
a
bly d
er
i
ve
di
n a manner ot
h
er t
h

an
by
t
h
e
d
e
g
ra
d
at
i
on
of
ur
i
cac
id
.T
h
eex
i
stence o
f
an orn
i
t
hi
ne c
y

c
l
e
f
or urea
p
ro
d
uct
i
on, suc
h
as
i
s
f
oun
di
n
verte
b
rates,
h
as not
b
een prove
d
conc
l
us

i
ve
l
y, even t
h
oug
h
t
h
e const
i
tuent mo
l
ecu
l
es o
f
t
h
e
cycle (arginine, ornithine, and citrulline) and the enzyme arginase have been identified in
several species (Cochran, 1975). Cochran (1985) suggested that urea is merely a by-produc
t
of
t
h
e
bi
oc
h

em
i
ca
l
convers
i
on o
f
ar
gi
n
i
ne to
p
ro
li
ne, use
di
n
fligh
t meta
b
o
li
sm (C
h
a
p
ter 14,
Section 3.3.5). Similarl

y
, the wa
y
in which ammonia is
p
roduced (es
p
eciall
y
in those insects
i
nw
hi
c
hi
t
i
sama
j
or excretory mo
l
ecu
l
e)
i
s poor
l
yun
d
erstoo

d
.It
i
s genera
ll
y assume
d
to
r
esult from deamination of amino acids, but the precise way in which this occurs remains
u
nclear
.
I
t has been su
gg
ested that the most
p
rimitive state was that in which the com
p
lete series
of
ur
i
co
ly
t
i
c enz
y

mes was
p
resent, an
d
ammon
i
a was t
h
e excretor
y
mater
i
a
l
.As
i
nsects
b
e-
came more
i
n
d
epen
d
ent o
f
water, se
l
ect

i
on pressures
l
e
d
to
l
oss o
f
t
h
e term
i
na
l
enzymes an
d
production of more appropriate excretory molecules. This simple view should be regarde
d
w
ith caution. Thus, in some caterpillars, diet can affect the nature of the nitrogenous waste
.
I
n certain insects substantial
q
uantities of a
p
articular nitro
g
enous waste molecule are

p
ro-
d
uce
d
,
y
et t
h
ea
pp
ro
p
r
i
ate enz
y
me
i
nt
h
eur
i
co
ly
t
i
c
p
at

h
wa
yh
as not
b
een
d
emonstrate
d
,
an
d
v
i
ce versa; t
h
at
i
s, t
h
ee
ff
ects o
f
ot
h
er meta
b
o
li

c
p
at
h
wa
y
sma
y
overr
id
et
h
eur
i
co
ly
t
i
c
system. In many
i
nsects (espec
i
a
ll
yen
d
opterygotes) t
h
e pre

d
om
i
nant n
i
trogenous excretor
y
product changes during development. For example, in the mosquit
o
Ae
d
es aegypt
i
urea is
t
he
p
rinci
p
al nitro
g
enous waste in the (a
q
uatic) larvae, while uric acid becomes dominant i
n
p
u
p
ae an
d

a
d
u
l
t
f
ema
l
es (von Dun
g
ern an
d
Br
i
e
g
e
l
, 2001). I
n
Pieri
sb
ra
ss
ica
e
(
Le
pid
o

p
tera)
th
ema
j
or excretor
yp
ro
d
uct
i
nt
h
e
p
u
p
aan
d
a
d
u
l
t
i
sur
i
cac
id
;

i
nt
h
e
l
arva t
hi
s com
p
oun
d
const
i
tutes on
l
ya
b
out 20% o
f
t
h
en
i
trogenous waste, a
ll
anto
i
cac
id b
e

i
ng t
h
e pre
d
om
i
nan
t
e
nd product (Table 18.1). Indeed, in some Lepidoptera, the ratio of uric acid to allantoin
m
ay fluctuate widely from day to day (Razet, 1961, cited from Bursell, 1967). Of great
i
nterest will be determination of factors that stimulate inhibition or activation (de
g
radation
o
rs
y
nt
h
es
i
s?) o
f
ur
i
co
ly

t
i
c enz
y
mes so t
h
at t
h
e most su
i
ta
bl
e
f
orm o
f
n
i
tro
g
enous waste
i
s
pro
d
uce
d
un
d
erag

i
ven set o
f
con
di
t
i
ons.
3
.2. Physiology of Nitrogenous Excretion
Ur
i
cac
id i
s
p
ro
d
uce
di
nt
h
e
f
at
b
o
dy
an
d/

or Ma
lpighi
an tu
b
u
l
es (occas
i
ona
lly
t
h
e
midg
ut) an
d
re
l
ease
di
nto t
h
e
h
emo
ly
m
ph
.Howt
h

e
highly i
nso
l
u
bl
eur
i
cac
id i
s trans
p
orte
d
i
n the hemolymph remains unclear though the most likely means seems to be as the sodium
o
r potassium salt, or in combination with specific carrier proteins (Cochran, 198
5
). The uric
acid is secreted into the lumen of the tubules as the sodium or
p
otassium salt, alon
g
wit
h
o
t
h
er

i
ons, water, an
d
var
i
ous
l
ow-mo
l
ecu
l
ar-we
igh
tor
g
an
i
cmo
l
ecu
l
es. In a t
ypi
ca
li
nsect
,
f
or exam
pl

e
Di
x
ipp
u
s
,
secret
i
on occurs a
l
on
g
t
h
e ent
i
re
l
en
g
t
h
o
f
t
h
etu
b
u

l
e. No resor
p
t
i
o
n
of
mater
i
a
l
sta
k
es p
l
ace across t
h
etu
b
u
l
ewa
ll
,an
d
urate
l
eaves t
h

etu
b
u
l
e
i
nso
l
ut
i
on. In t
h
e
r
ectum resorption of water and sodium and potassium ions occurs, and the pH of the fluid
544
C
HAPTER
18
F
I
G
URE 18
.
4
.
Movements of water, ions, and or
g
anic molecules in the excretor
y

s
y
stems of (A
)
Di
x
ipp
u
s
a
n
d
(
B
)
Rh
o
dniu
s.
[
After R. H. Stobbart and J. Shaw, 1974, Salt and water balance: Excretion, in
:
T
he Physiology o
f
Insect
a
,2n
d
e

d
., Vo
l
. V (M. Roc
k
ste
i
n, e
d
.). B
yp
erm
i
ss
i
on o
f
Aca
d
em
i
c Press, Inc. an
d
t
h
e aut
h
ors.]
decreases from 6.8–7.
5

to 3.
5
–4.
5
. The combined effect of water resorption and pH chang
e
is to cause massive precipitation of uric acid. Useful organic molecules such as amino acid
s
and sugars are also resorbed through the rectal wall. The Malpighian tubule-rectal wal
l
excretor
y
s
y
stem thus shows certain functional analo
g
ies with the vertebrate ne
p
hron. The
excret
i
on o
f
ur
i
cac
id in
D
ixippus
i

s summar
i
ze
di
nF
ig
ure 18.4A
.
In
Rh
o
dniu
s
,w
h
ose tu
b
u
l
es s
h
ow structura
l diff
erent
i
at
i
on a
l
on

g
t
h
e
i
r
l
en
g
t
h
,t
h
e
p
ro
-
c
ess o
f
excret
i
on
i
s
b
as
i
ca
ll

yt
h
e same as
i
n
Di
x
ipp
us
.
However,
in
R
hod
niu
s
o
n
l
yt
he
d
istal portion of the tubule is secretory and resorption of water and cations begins in the
p
roximal
p
art. Sli
g
ht chan
g

ein
p
H occurs (from 7.2 to 6.6) as the fluid
p
asses alon
g
5
4
5
N
ITR
O
GEN
O
U
S
EXCRETION
A
ND
S
ALT AND
WA
TER BALANC
E
t
he tubule and this is sufficient to initiate uric acid precipitation. Further water and salt
r
esor
p
tion occurs in the rectum (

p
H 6.0), causin
gp
reci
p
itation of the remainin
g
waste
(
F
ig
ure 18.4B).
A
l
t
h
ou
gh
a
ll
anto
i
n
i
st
h
ema
j
or n
i

tro
g
enous waste
i
n man
yi
nsects,
i
ts mo
d
eo
f
excret
i
on
appears to
h
ave
b
een stu
di
e
di
non
l
y one spec
i
es, Dysdercus fasciatus
(
Hem

i
ptera) (Berr
id
ge
,
196
5
). This insect is required, because of its diet, to excrete large quantities of unwanted
i
ons (ma
g
nesium,
p
otassium, and
p
hos
p
hate). This, combined with the insect’s inabilit
y
t
o
act
i
ve
ly
resor
b
water
f
rom t

h
e rectum, resu
l
ts
i
nt
h
e
p
ro
d
uct
i
on o
f
a
l
ar
g
evo
l
ume o
f
ur
i
ne.
Because no resor
p
t
i

on or ac
idi
ficat
i
on occurs w
hi
c
h
cou
ld
cause
p
rec
ipi
tat
i
on o
f
ur
i
cac
id,
thi
smo
l
ecu
l
e
i
sno

l
onger use
d
as an excretory pro
d
uct. T
h
us, a
ll
anto
i
n, w
hi
c
hi
s10t
i
mes
m
ore soluble than uric acid (yet of equally low toxicity), is preferred. However, the insec
t
d
oes not possess a mechanism for actively transporting this molecule from the hemolymph
t
otu
b
u
l
e
l

umen; t
h
at
i
s, a
ll
anto
i
non
ly
moves
p
ass
i
ve
ly
across t
h
ewa
ll
o
f
t
h
etu
b
u
l
e. It
is

th
ere
f
ore ma
i
nta
i
ne
di
n
high
concentrat
i
on
i
nt
h
e
h
emo
ly
m
ph
to ac
hi
eveasu
f
fic
i
ent rate o

f
diff
us
i
on
i
nto t
h
etu
b
u
l
e. W
h
et
h
eras
i
m
il
ar mec
h
an
i
sm occurs
i
not
h
er a
ll

anto
i
n-excret
i
n
g
i
nsects remains to be seen. It may be significant that many other allantoin producers are
h
erbivorous and have the problem of removing large quantities of unwanted ions.
The
p
h
y
siolo
g
ical mechanisms for excretion of other nitro
g
enous wastes are
p
oorl
y
un
-
d
erstoo
d
.A
q
uat

i
c
i
nsects are
p
resume
d
to excrete ammon
i
a
i
nver
y dil
ute ur
i
ne, w
h
ereas
l
ar
-
va
eof
m
eat-eat
i
ng
fli
es suc
h

as Lucilia cu
p
rin
a
a
n
d
S. bullata
p
ro
d
uce
hi
g
hl
y concentrate
d
,
ammonia-rich excreta, apparently by actively transporting ammonium ions across the ante
-
r
ior hindgut wall. Urea probably moves passively into the Malpighian tubules and becomes
concentrated in the hind
g
ut because of its inabilit
y
to
p
ermeate the cuticular linin
g

as water
r
esor
p
t
i
on occurs.
3
.3.
S
torage Excretion
An alternative strate
gy
to the removal of wastes throu
g
h the Mal
p
i
g
hian tubule-rectum
s
y
stem use
dby
some
i
nsects
i
s stora
g

e excret
i
on, t
h
e retent
i
on o
f
t
h
e wastes
i
n “out o
f
t
he
way
pl
aces” w
i
t
hi
nt
h
e
b
o
dy
.InDysdercu
s

,f
or exam
pl
e, ur
i
cac
id i
s
d
e
p
os
i
te
dp
ermanent
ly
i
nt
h
eep
id
erma
l
ce
ll
so
f
t
h

ea
bd
omen,
f
orm
i
ng
di
st
i
nct, w
hi
te transverse
b
an
d
s (Berr
id
ge,
196
5
). Adult Lepidoptera convert much of their waste nitrogen into pteridines that are stored
i
n the integument, eyes, or wing scales, giving the insects their characteristic color pattern
s
(
Cha
p
ter 11, Section 4.3)
.

A
tot
h
er t
i
mes stora
g
eo
f
urate occurs even w
h
en t
h
etu
b
u
l
es are wor
ki
n
g
norma
lly
a
n
d
may
b
e regar
d

e
d
as a supp
l
ementary excretory mec
h
an
i
sm
f
or occas
i
ons w
h
en t
he
t
ubules cannot cope with all the waste that is being produced. In the larval stages of many
species uric acid crystallizes out in ordinary fat body cells and epidermis, even though the
Mal
p
i
g
hian tubules are functional. It a
pp
ears that this is caused b
y
the metabolic activit
y
o

f
t
h
ece
ll
st
h
emse
l
ves (
i
.e., t
h
e
y
are not accumu
l
at
i
n
g
ur
i
cac
id f
rom t
h
e
h
emo

ly
m
ph
)
,
a
n
d
cr
y
sta
lli
zat
i
on occurs
by
v
i
rtue o
f
t
h
e
p
art
i
cu
l
ar con
di

t
i
ons (
p
H,
i
on
i
c content, etc.)
e
xisting in the cells. During the later stages of pupation the crystals disappear, the uri
c
a
cid apparently having been transferred to the meconium (the collective wastes of pupal
m
etabolism, released at eclosion) via the excretor
y
s
y
stem. It is worth notin
g
that in man
y
s
p
ec
i
es t
h
eMa

lpighi
an tu
b
u
l
es are ent
i
re
ly
reconst
i
tute
dd
ur
i
n
g
t
h
e
p
u
p
a
l
sta
g
e. T
h
us,

stora
g
eo
f
ur
i
cac
id i
n
f
at
b
o
dy
an
d
e
pid
erma
l
ce
ll
s
i
so
fg
reat
i
m
p

ortance at t
hi
st
i
me. Ye
t
ot
h
er
i
nsects, nota
bl
y term
i
tes an
d
coc
k
roac
h
es, reta
i
n
l
arge quant
i
t
i
es o
f

ur
i
cac
id i
n spec
i
a
l
cells (urocytes) within the fat body. However, as Cochran (198
5
) pointed out, this is not a
5
4
6
C
HAPTER
18
f
orm of storage excretion but an important means of conserving nitrogen in these insects
w
hose normal diet is severel
y
nitro
g
en deficient (Cha
p
ter 16, Section 5.1.1).
T
em
p

orar
y
stora
g
eo
f
ot
h
er mater
i
a
l
sma
y
a
l
so ta
k
e
pl
ace. Ca
l
c
i
um sa
l
ts (es
p
ec
i

a
lly
c
ar
b
onate an
d
oxa
l
ate) are
f
oun
di
nt
h
e
f
at
b
o
d
yo
f
many p
l
ant-eat
i
ng
i
nsect

l
arvae. Dur
i
n
g
metamorphosis they are released and dissolved, to be excreted via the Malpighian tubules
in the adult. Dyes present in food are often accumulated in fat body cells where they appear
to become associated with
p
articular
p
roteins. These
p
roteins are then transferred to the e
gg
d
ur
i
n
g
v
i
te
ll
o
g
enes
i
san
d

t
h
e
dy
es su
b
se
q
uent
ly
“excrete
d
”
d
ur
i
n
g
ov
ip
os
i
t
i
on.
N
e
ph
roc
y

tes (C
h
a
p
ter 17, Sect
i
on 2) accumu
l
ate a var
i
et
y
o
f
su
b
stances, es
p
ec
i
a
lly
p
igments, and their name is derived from the mistaken idea that storage excretion is one o
f
their major functions. As Locke and Russell (1998) pointed out, nephrocytes are involved
in the metabolism of hemol
y
m
p

h macromolecules
.
4
.
S
alt and Water Balanc
e
Salt and water balance involves more than sim
p
l
y
the control of hemol
y
m
p
h osmotic
p
ressure; t
h
ere
l
at
i
ve
p
ro
p
ort
i
ons o

f
t
h
e
i
ons t
h
at contr
ib
ute to t
hi
s
p
ressure must
b
ema
i
n-
ta
i
ne
d
w
i
t
hi
n narrow
li
m
i

ts. T
h
e osmot
i
c
p
ressure o
f
t
h
e
h
emo
ly
m
ph i
s
g
enera
lly
w
i
t
hi
n
t
h
e same
li
m

i
ts as t
h
at o
f
t
h
e
bl
oo
d
o
f
ot
h
er organ
i
sms,
b
ut
i
t can
b
e
i
ncrease
d
cons
id
era

bly
under specific conditions (by the addition, for example, of glycerol, which serves as an
antifreeze durin
g
hibernation). Re
g
ulation of the salt and water content is obviousl
y
related
to t
h
e nature o
f
t
h
e externa
l
env
i
ronment
.
Insects
i
n
diff
erent
h
a
bi
tats

f
ace
diff
erent osmot
ic
p
ro
bl
ems. Nevert
h
e
l
ess, t
h
ese
p
ro
bl
ems
h
ave
b
een so
l
ve
d
us
i
n
g

t
h
e same
b
as
i
c mec
h
an
i
sm
,
name
l
y, t
h
e pro
d
uct
i
on o
f
a “pr
i
mary excretory
fl
u
id
”
i

nt
h
eMa
l
p
i
g
hi
an tu
b
u
l
es
f
o
ll
owe
d
by differential resorption from or secretion into this fluid when it reaches the rectum. Fo
r
c
larity the problems of insects living on land, in fresh water, or in brackish or salt water are
c
ons
id
ere
d
se
p
arate

ly
. However, cons
id
era
bl
es
i
m
il
ar
i
t
yi
nt
h
eso
l
ut
i
on o
f
t
h
ese
p
ro
bl
ems
will b
e seen

.
4.
1
. Terrestr
i
al Insects
T
errestrial insects a
pp
ear able to re
g
ulate their hemol
y
m
p
h osmotic
p
ressure over a
wid
e ran
g
eo
f
con
di
t
i
ons. For exam
pl
e,

in
T
ene
b
ri
o
t
h
e
h
emo
ly
m
ph
osmot
i
c
p
ressure var
i
es
o
nly from 223 to 36
5
mM/l (measured as the equivalent of a sodium chloride solution
)
o
v
e
ra

r
ange of relative humidity from 0% to 100% (Marcuzzi, 19
5
6, cited in Stobbart and
S
haw, 1974). In starvin
g
S
c
h
istocerc
a
there is only a 30% difference in hemolymph osmotic
p
ressure between animals ke
p
t in air at 100% relative humidit
y
and
g
iven onl
y
ta
p
water
an
d
t
h
ose

k
e
p
t
i
na
i
r at 70% re
l
at
i
ve
h
um
idi
t
y
an
dgi
ven sa
li
ne (osmot
i
c
p
ressure e
q
u
i
va

l
ent
to
5
00 mM/l sodium chloride) to drink (Philli
p
s, 1964a)
.
In terrestrial insects water is lost (1) by evaporation across the integument, although
this is considerably reduced by the presence of the wax layer in the epicuticle (Chapter 11
,
S
ection 2); (2) durin
g
res
p
iration throu
g
h the s
p
iracles [man
y
insects
p
ossess devices both
p
h
y
siolo
g

ical and structural for reducin
g
the loss (Cha
p
ter 15, Section 2.2)]; and (3) durin
g
excret
i
on. Des
pi
te t
h
ese a
d
a
p
tat
i
ons,
i
nsects t
h
at
i
n
h
a
bi
t extreme
ly d

r
y
env
i
ronments ma
y
become greatly dehydrated. For example, some desert beetles can survive the loss of 7
5%
o
f their body water. The critical factor for these beetles is to maintain the intracellular
w
ater concentration b
y
usin
g
the water in the hemol
y
m
p
h; in other words, the hemol
y
m
p
h
5
4
7
N
ITR
O

GEN
O
U
S
EXCRETION
A
ND
S
ALT AND
WA
TER BALANC
E
volume is reduced. To avoid the potential osmotic problems that this withdrawal of wate
r
creates, osmoticall
y
active
p
articles can be excreted or rendered inactive; for exam
p
le, ions
are c
h
e
l
ate
d
an
d
am

i
no ac
id
s are
p
o
ly
mer
i
ze
di
nto
p
e
p
t
id
es. T
h
e strate
gy
use
d
a
pp
ears to
b
e corre
l
ate

d
w
i
t
h
t
h
e
i
nsects’
di
et: carn
i
vorous s
p
ec
i
es, w
h
ose
f
oo
d
conta
i
ns a
b
un
d
ant

so
di
um, ten
d
to excrete t
h
e excess
i
ons. T
h
e
di
et o
fh
er
bi
vores,
b
y contrast,
i
s
d
efic
i
ent
in
sodium, so these species use chelation as a means of retaining the sodium within the body
(
Pedersen and Zachariassen, 2002
)

.
T
h
ema
j
or source o
f
water
f
or most terrestr
i
a
li
nsects
i
so
b
v
i
ous
ly f
oo
d
an
dd
r
i
n
k
. Som

e
i
nsects ma
y
eat excess
i
ve
ly
so
l
e
ly f
or t
h
e water content o
f
t
h
e
f
oo
d
.W
h
ere su
f
fic
i
ent water
cannot

b
eo
b
ta
i
ne
db
y
d
r
i
n
ki
ng or
i
n
f
oo
d
,t
h
e
i
nsect must o
b
ta
i
n
i
t

b
yot
h
er means. On
e
source is the water produced during metabolism. Absorption of water vapor from the atmo
-
sphere is a method employed by a few insects (e.g., T
h
ermobi
a
an
d
T
enebri
o
)
that are nor
-
m
a
lly f
oun
di
nver
yd
r
y
con
di

t
i
ons. Interest
i
n
gly
,t
h
es
i
te o
f
a
b
sor
p
t
i
on
i
st
h
e rectum, w
hi
c
h
,
as
i
s note

db
e
l
ow,
i
st
h
es
i
te o
f
u
p
ta
k
eo
f liq
u
id
water
i
not
h
er terrestr
i
a
l
an
d
sa

l
twater
i
nsects
.
S
ma
ll
amounts o
fi
ons are
l
ost
f
rom t
h
e
b
o
d
yv
i
at
h
e excretory system, an
d
t
h
ese ar
e

r
eadily made up by absorption across the midgut wall. Indeed, in terrestrial insects the usual
problem is removal of unwanted ions present in the diet. The food often contains ions i
n
concentrations that are widel
y
different from those of the hemol
y
m
p
h. It is
p
robable that
th
ese
i
ons enter t
h
e
h
emo
ly
m
ph p
ass
i
ve
ly i
nt
h

e same
p
ro
p
ort
i
ons as t
h
e
y
occur
i
nt
h
e
di
et
,
an
d
excesses are su
b
sequent
l
y expe
ll
e
d
v
i

at
h
e excretory system. In ot
h
er wor
d
s, t
h
em
id
gut
d
oes not act as a selectively permeable barrier to the entry of ions (Stobbart and Shaw, 1974)
.
The role of the Malpighian tubules and rectum was investigated by examination of th
e
i
onic com
p
osition of the fluids within them and, more recentl
y
,b
y
the use of radioisoto
p
es
t
o measure t
h
e

di
rect
i
on an
d
rate o
f
movement o
fi
n
di
v
id
ua
li
ons. T
h
e stu
di
es o
f
Ramsa
yi
n
t
he 1950s (see reviews for references) revealed that the fluid in the tubules is isosmotic wit
h
th
e
h

emo
l
ymp
h
(Ta
bl
e 18.2)
b
ut
h
as a very
diff
erent
i
on
i
c compos
i
t
i
on. Part
i
cu
l
ar
l
yo
b
v
i

ou
s
i
s the difference in potassium ion concentration, which is several times higher in the tubule
fluid than in the hemol
y
m
p
h. The sodium ion concentration is usuall
y
lower in the fluid
th
an
i
nt
h
e
h
emo
ly
m
ph
,as
i
st
h
e case w
i
t
h

most ot
h
er
i
ons (exce
p
t
ph
os
ph
ate). T
h
etu
b
u
l
e
fl
u
id
,w
hi
c
hi
s
p
ro
d
uce
d

cont
i
nuous
ly
,a
l
so conta
i
ns a num
b
er o
fl
ow-mo
l
ecu
l
ar-we
igh
t
o
rgan
i
cmo
l
ecu
l
es,
f
or examp
l

e, am
i
no ac
id
san
d
sugars; t
h
us,
i
t
i
s
b
roa
dl
y compara
ble
w
ith the glomerular filtrate of the vertebrate kidney, though it is not produced by hydrostati
c
pressure. The high potassium concentration in the tubule fluid and the demonstration that the
r
ate at which tubule fluid is formed de
p
ends on the hemol
y
m
p
h

p
otassium concentratio
n
l
e
d
Ramsa
y
to su
gg
est t
h
at t
h
e act
i
ve trans
p
ort o
fp
otass
i
um
i
ons
i
s
f
un
d

amenta
l
to t
h
e
pro
d
uct
i
on an
dfl
ow o
f
t
h
e
fl
u
id
.B
l
oo
d
suc
ki
ng
i
nsects t
h
at

h
ave
j
ust
f
e
d
are except
i
ona
l
i
n that both potassium and sodium ions are actively transported into the tubule lumen
.
This modification to the basic plan is necessitated by the heavy sodium chloride load in
t
he
p
lasma fraction of the vertebrate host’s blood and b
y
the need to remove as ra
p
idl
y
a
s
p
oss
ibl
e excess water ta

k
en
i
nto t
h
e
b
o
dy
as a resu
l
to
ff
ee
di
n
g
. Act
i
ve cat
i
on trans
p
or
t
i
s accom
p
an
i

e
dby
t
h
e movement o
f
an
i
ons (
p
r
i
nc
ip
a
lly
c
hl
or
id
e) to ma
i
nta
i
ne
l
ectr
i
ca
l

n
eutrality and by the flow of water into the tubule lumen by osmosis (Pannabecker, 199
5
)
.
M
ost other ions and organic molecules appear to enter the tubule fluid passively. How
-
ev
e
r, active trans
p
ort of sulfate and of some d
y
es and toxic com
p
ounds (e.
g
., alkaloids) has
b
een
d
emonstrate
di
n some
i
nsects, nota
bly
t
h

ose s
p
ec
i
es t
h
at encounter t
h
ese mo
l
ecu
l
es
i
nt
h
e
i
r natura
ldi
et
.
I
t
i
sc
l
ear t
h
at, as t

h
etu
b
u
l
e
fl
u
id
an
dh
emo
l
ymp
h
are
i
sosmot
i
c, t
h
etu
b
u
l
es are no
t
d
irectly concerned with regulation of hemolymph osmotic pressure. Ramsay, using isolated
5

48
C
HAPTER
18
T
ABLE 18
.
2
.
The Osmotic Pressure and Concentration
(
mM/l
)
of Some Ions in the
H
emo
l
ymp
h
(H), Ma
l
p
i
g
hi
an Tu
b
u
l
eF

l
u
id
(MT), an
d
Recta
l
F
l
u
id
(R)
i
n Insects
f
ro
m
D
iff
erent Ha
bi
tats
a
I
on
s
Osmot
i
c pressure
Habitat Species (stage and conditions) Fluid

(
≡
NaCl solution) Na
+
K
+
C
l
−
Te
rr
est
r
ial
Sc
h
istocerca
g
re
g
aria
H
214
1
08 11 115
(
a
d
u
l

t, water-
f
e
d)
MT
2
2
6
20 13
99
3
R
4
33
122
5
Di
x
ipp
us morosus
H
17
1111
887
(adult, feeding)
MT
171
5
14
565

R
390
18 32
7
—
R
h
o
d
nius pro
l
ixu
s
(a
d
u
l
t,
H
2
0
6
1
74 7 155
1
9–29
h
ra
f
ter mea

l)
MT
2
2
8
1
14 104 180
R
358
161 1
9
1
—
S
alt wate
r
A
ede
s
detritu
s
(
larvae,
H
157
—
—
—
in seawater)
MT

—
———
R
5
3
7
———
A
e
d
es
d
etritus
(l
arvae,
H
97
———
i
n
di
st
ill
e
d
water
)
MT
—
———

R5
6
——
—
F
r
es
h
wate
r
A
edes aeg
y
pti
(
larvae,
H
138
87 3 —
i
n distilled water)
MT
130
24 88 —
R1
24
2
5
—
a

D
ata mainl
y
from Stobbart and Shaw (1974)
.
tu
b
u
l
es, s
h
owe
d
t
h
at t
h
e
i
sosmot
i
c con
di
t
i
on
i
s reta
i
ne

d
over a w
id
e ran
g
eo
f
externa
l
c
oncentrat
i
ons. In
di
rect
l
y,
h
owever, t
h
etu
b
u
l
es are
i
mportant
i
nregu
l

at
i
on, as t
h
e rate at
w
hich ions and water are excreted from the body is the difference between their rate of
secretion into the tubule lumen and their rate of resor
p
tion b
y
the rectum.
A
s note
di
n Sect
i
on 3.2,
i
n some
i
nsects t
h
etu
b
u
l
es s
h
ow re

gi
ona
l diff
erent
i
at
i
on,
secret
i
on ta
ki
ng p
l
ace
i
nt
h
e
di
sta
l
part an
d
resorpt
i
on
b
eg
i

nn
i
ng
i
nt
h
e prox
i
ma
l
part o
f
t
h
e
tubule. In most species, however, resorption occurs mainly in the rectum, though the ileum
ma
y
also modif
y
the fluid. In the rectum ma
j
or chan
g
es occur in the osmotic
p
ressure and
c
om
p

os
i
t
i
on o
f
t
h
eur
i
ne (Ta
bl
e 18.2). Genera
lly
,t
h
eur
i
ne
b
ecomes
g
reat
ly hyp
erton
i
ct
o
t
h

e
h
emo
l
ymp
h
,
b
ut w
h
en muc
h
water
i
sava
il
a
bl
ea
h
ypoton
i
c
fl
u
id
may
b
e excrete
d

.
In the rectum, water is resorbed against a concentration gradient; that is, it is an activ
e
p
rocess and ener
gy
is ex
p
ended. Philli
p
s (1964a) showed that in
S
chistocerca
t
h
e
r
ate o
f
w
ater movement across t
h
e recta
l
wa
ll i
s
i
n
d

e
p
en
d
ent o
f
t
h
e rate o
f
sa
l
t accumu
l
at
i
on. T
h
e
rate at which water is resorbed depends on the osmotic gradient across the wall, and, as
the
g
radient increases durin
g
resor
p
tion, the
p
oint is reached at which the rate of active
accumu

l
at
i
on
i
s
b
a
l
ance
dby
t
h
e rate o
fp
ass
i
ve
diff
us
i
on
b
ac
ki
nto t
h
e recta
ll
umen; t

h
at
i
s,
t
h
e concentrat
i
on o
f
t
h
e recta
lfl
u
id
reac
h
es a max
i
mum va
l
ue. However
,
t
hi
sva
l
ue var
i

es
according to the water requirements of the insect. For example, locusts that have been kept
inadr
y
environment and
g
iven stron
g
saline to drink have a rectal fluid whose osmotic
p
ressure
i
sa
b
out tw
i
ce t
h
at o
fi
nsects w
i
t
h
access to ta
p
water. T
h
e
phy

s
i
o
l
o
gi
ca
lb
as
i
so
f
t
hi
s
i
ncrease
d
a
bili
ty to concentrate t
h
eur
i
ne
i
s not
k
nown
.

T
he precise mechanism of water uptake is still unclear. Though models have bee
n
p
ro
p
osed in which wate
r
per
s
e
i
s activel
y
trans
p
orted across the rectal wall, there is now
54
9
N
ITR
O
GEN
O
U
S
EX
C
RETION
A

ND
S
ALT AND
WA
TER B
A
L
A
NC
E
d
irect evidence that water movements occur as a result of active movements of inorgani
c
i
ons, es
p
eciall
y
sodium,
p
otassium, and chloride (secondar
y
trans
p
ort of water) (Philli
p
s,
1977). F
i
ne-structura

l
stu
di
es o
f
t
h
e recta
l
wa
ll
o
f
Calliphora (Berr
idg
ean
d
Gu
p
ta, 19
6
7),
Peri
p
laneta (Osc
h
man an
d
Wa
ll

,19
6
9) an
d
ot
h
er
i
nsects, an
d
t
h
ee
l
e
g
ant wor
k
o
f
Wa
ll
an
d
Osc
h
man (1970) an
d
Wa
ll

e
ta
l.
(1970), w
h
o use
d
m
i
cropuncture to o
b
ta
i
n
fl
u
id
samp
l
es
from the subepithelial sinus and intercellular spaces in the rectal epithelium, led to the
followin
g
scheme for water absor
p
tion from the rectum (Fi
g
ure 18.5). Ions are activel
y
secrete

di
nto t
h
e
i
nterce
ll
u
l
ar s
p
ace
b
etween t
h
e
highly
convo
l
ute
dpl
asma mem
b
ranes
o
f
a
dj
acent e
pi

t
h
e
li
a
l
ce
ll
ssot
h
at
l
oca
lp
oc
k
ets o
f high
sa
l
t content are
f
orme
d
.T
h
us,
an osmot
i
c gra

di
ent
i
s
d
eve
l
ope
dd
own w
hi
c
h
water
fl
ows
f
rom t
h
e recta
ll
umen to t
he
i
ntercellular spaces via the cytoplasm of the epithelial cells. Water may also enter th
e
i
ntercellular spaces directly from the rectal lumen if the apical septate junctions are leaky
as
h

as
b
een
p
ro
p
ose
d
.T
h
e entr
y
o
f
water
i
nto t
h
es
p
aces
p
ro
d
uces a
hyd
rostat
i
c
p

ressure
th
at
f
orces t
h
e
i
ons an
d
water towar
d
t
h
e
h
emo
ly
m
ph
.Ast
h
e
fl
u
id
moves t
h
rou
gh

t
h
e
l
ar
g
er
(i
nner)
i
nterce
ll
u
l
ar spaces an
d
su
b
ep
i
t
h
e
li
a
l
s
i
nus, act
i

ve resorpt
i
on o
fi
ons occurs across
t
he epithelial cell membrane. However, relatively little water moves into the cells because
t
he spaces have a low surface area/volume ratio (i.e., the plasma membrane of the cells i
s
n
ot convoluted in these re
g
ions as it is in the distal intercellular s
p
aces).
Ramsa
y
’s ear
ly
wor
k
on Rh
o
dniu
s
an
d
Dixippu
s

p
rov
id
e
d
a stron
gi
n
di
cat
i
on t
h
at t
h
e
r
ectum
i
sa
l
so capa
bl
eo
f
resor
bi
ng sa
l
ts, an

d
t
hi
s
h
as
b
een confirme
db
yP
hilli
ps (19
6
4
b
)
i
n
S
c
h
istocerca. This author showed that sodium, potassium, andchloride ions are accumulate
d
F
I
G
URE 18
.
5
.

Scheme to ex
p
lain water absor
p
tion from the rectum. Active secretion of solute into the intercel-
l
u
l
ar c
h
anne
l
s
i
n
d
uces pass
i
ve movement o
f
water
i
nto t
h
ec
h
anne
l
s
f

rom t
h
eep
i
t
h
e
li
a
l
ce
ll
san
d
, per
h
aps,
di
rect
ly
f
rom t
h
e recta
ll
umen. T
h
e
i
nterce

ll
u
l
ar
fl
u
id
t
h
us
f
orme
dfl
ows towar
d
t
h
e
h
emocoe
l
,an
d
,as
i
tmovest
h
rou
gh
t

h
e
s
inuses, solute is actively resorbed by the cells for recycling. For further details, see text. [After S. H. P. Maddrell,
1971, T
h
e mec
h
an
i
sms o
fi
nsect excretory systems,
Ad
v. Insect P
h
ysio
l.
8
:199–331. By perm
i
ss
i
on o
f
Aca
d
em
ic
P

ress, Lt
d
.an
d
t
h
e aut
h
or.
]
5
5
0
C
HAPTER
18
against a concentration gradient and independently of the movement of water. Furthermore
,
the rate of accumulation of these ions de
p
ends on their concentrations in the rectal fluid
an
d
t
h
e
h
emo
ly
m

ph
.Int
hi
swa
y
t
h
ere
q
u
i
rements o
f
t
h
e
i
nsect can
b
e sat
i
sfie
d
. In water-
f
e
d
l
ocusts
i

ons are resor
b
e
df
rom t
h
e rectum as
q
u
i
c
kly
as t
h
e
y
arr
i
ve
i
nt
h
e
fl
u
id f
rom t
he
tu
b

u
l
es, an
dl
ow recta
l
concentrat
i
ons are
f
oun
d
(Ta
bl
e 18.2). At t
h
eot
h
er extreme,
i
nsa
li
ne
-
f
ed animals, the rates of resorption are low and a greatly hyperosmotic fluid is produced
.
T
he cr
yp

tone
p
hridial arran
g
ement of Mal
p
i
g
hian tubules increases the
p
ower of th
e
recta
l
wa
ll
to resor
b
water a
g
a
i
nst
high
concentrat
i
on
g
ra
di

ents. T
h
es
y
stem
i
s
p
art
i
cu
l
ar
ly
w
e
ll d
eve
l
o
p
e
di
n
i
nsects t
h
at
i
n

h
a
bi
t
d
r
y
env
i
ronments, ena
bli
n
g
suc
h
s
p
ec
i
es not on
ly
to
extract t
h
e max
i
mum amount o
f
water
f

rom t
h
e
i
r
f
eces
b
ut a
l
so, un
d
er
f
ast
i
ng con
di
t
i
ons,
to take up water from moist air (relative humidity at least 88%) by holding open their anus
(Machin, 1980). According to Ramsay (1964), the perinephric membrane is impermeable
to water, an
d
,un
d
er
d
r

y
con
di
t
i
ons, t
h
e osmot
i
c
p
ressure o
f
t
h
e
p
er
i
ne
ph
r
i
ccav
i
t
yi
sra
i
se

d
ma
i
n
ly b
ecause o
f
t
h
e
p
resence o
fp
otass
i
um c
hl
or
id
e. T
h
us, t
h
e concentrat
i
on
g
ra
di
ent

across t
h
e recta
l
wa
ll i
sre
d
uce
d
,
f
ac
ili
tat
i
ng water upta
k
e. Ramsay suggeste
d
t
h
at potass
i
um
and chloride ions are actively transported into the lumen of the perirectal tubules (whic
h
c
ontain many mitochondria), with an accompanying movement of water. Resorption of ions
and water occurs across the wall of the

p
arts of the tubule bathed in hemol
y
m
p
h. An a
pp
arent
l
ac
k
o
f
m
i
toc
h
on
d
r
i
a
i
nt
h
e
p
er
i
ne

ph
r
i
c mem
b
rane an
dl
e
p
to
ph
ra
g
ma ce
ll
s
l
e
d
Ramsa
y
to
c
onc
l
u
d
et
h
at

i
ons move pass
i
ve
l
y across t
h
e mem
b
rane
i
nor
d
er to
b
a
l
ance t
h
ose remove
d
by the tubule. However, the fine-structural and experimental study of Grimstone
e
ta
l.
(
1968
)
has shown this conclusion to be wrong. These authors found that the leptophragma cells
have a normal com

p
lement of mitochondria. Active trans
p
ort of
p
otassium ions occur
s
across t
h
ece
ll
s, w
hi
c
h
are,
h
owever,
i
m
p
ermea
bl
e to water. C
hl
or
id
e
i
ons

f
o
ll
ow
p
ass
i
ve
ly
.
Th
esc
h
eme
i
s summar
i
ze
di
nF
ig
ure 18.2D.
4
.
2
.
F
reshwater
I
nsect

s
In
f
res
h
water
i
nsects water enters t
h
e
b
o
dy
osmot
i
ca
lly d
es
pi
te t
h
ere
l
at
i
ve
ly i
m
p
erme

-
a
bl
e cut
i
c
l
e(C
h
a
p
ter 11, Sect
i
on 4.2) an
d
must
b
e remove
d
,an
d
sa
l
ts w
ill b
e
l
ost
f
rom t

he
b
o
d
yan
d
must
b
e rep
l
ace
dif
t
h
e
h
yperosmot
i
c con
di
t
i
on o
f
t
h
e
h
emo
l

ymp
hi
sto
b
ema
i
n
-
tained. Freshwater insects can regulate their hemolymph osmotic pressure successfully t
o
the point at which the external environment becomes isosmotic with the hemolymph (Figure
1
8.6). This is achieved b
y
the
p
roduction of urine that is h
yp
oosmotic to the hemol
y
m
p
h
.
B
e
y
on
d
t

hi
s
p
o
i
nt, re
g
u
l
at
i
on
b
rea
k
s
d
own
b
ecause
f
res
h
water
i
nsects are not a
bl
eto
p
ro

d
uc
e
h
yperosmot
i
cur
i
ne; t
h
at
i
s, t
h
ey cannot resor
b
water aga
i
nst a concentrat
i
on gra
di
ent or ex
-
c
rete excess ions (Stobbart and Shaw, 1974). In other words, they become osmoconformers
,
their hemolymph osmotic pressure closely paralleling that of the external medium
.
As in terrestrial insects, the Mal

p
i
g
hian tubules
p
roduce a fluid that is isosmotic with
t
h
e
h
emo
ly
m
ph b
ut o
f diff
erent
i
on
i
c com
p
os
i
t
i
on. Part
i
cu
l

ar
ly
o
b
v
i
ous
i
st
h
e
g
reat
diff
er
-
ence
i
nt
h
e
p
otass
i
um
i
on concentrat
i
on
b

etween t
h
etwoso
l
ut
i
ons, as a resu
l
to
f
act
i
v
e
transport (Table 18.2). When the primary urine enters the rectum, resorption of ions oc
-
c
urs. The osmotic pressure of the fluid that finally leaves the body is much lower than tha
t
o
f the hemol
y
m
p
h but not as low as would be ex
p
ected from knowled
g
e of the extent of
i

on resor
p
t
i
on
i
nt
h
e rectum. T
hi
s
i
s
b
ecause
l
ar
g
e
q
uant
i
t
i
es o
f
ammon
i
um
i

ons a
pp
ear
i
nt
h
e recta
lfl
u
id
.T
h
ese
i
ons cannot
b
e
d
etecte
di
nt
h
eMa
lpighi
an tu
b
u
l
es, an
di

t
i
s
p
re-
sume
d
t
h
at t
h
ey are secrete
ddi
rect
l
y across t
h
e recta
l
wa
ll
, as occurs
i
n
l
arvae o
f
S. bu
ll
ata

(
Section 2.2
)
.
55
1
N
ITR
O
GEN
O
U
S
EXCRETION
A
ND
S
ALT AND
WA
TER BALANC
E
F
I
GU
RE 18
.
6
.
Th
ere

l
at
i
ons
hip b
etween osmot
i
c
p
ressure o
f
t
h
e
h
emo
ly
m
ph
an
d
t
h
at o
f
t
h
e externa
l
me

di
um
in some freshwater insects. [After J. Shaw and R. H. Stobbart, 1963, Osmotic and ionic re
g
ulation in insects
,
Ad
v.
I
nsect P
h
ysio
l
.
1
:315–399. By permission of Academic Press Ltd. and the authors.]
I
n
f
res
h
water
i
nsects,
f
oo
di
st
h
e usua

l
source o
fi
ons t
h
at are a
b
sor
b
e
d
t
h
rou
gh
t
h
e
mid
gut wa
ll
. However,
i
n some spec
i
es
i
ons are accumu
l
ate

d
t
h
roug
h
ot
h
er parts o
f
t
h
e
b
ody, for example, the gills of caddisfly larvae, the rectal respiratory chamber of dragonfly,
d
amselfly and mayfly larvae, the anal gills of syrphid larvae, and the anal papillae o
f
m
os
q
uito and mid
g
e larvae. The role of the anal
p
a
p
illae in ionic re
g
ulation has bee
n

p
art
i
cu
l
ar
ly
we
ll
stu
di
e
d
.Inmos
q
u
i
to
l
arvae a
p
a
i
ro
fp
a
pill
ae
i
s

l
ocate
d
on eac
h
s
id
eo
f
th
e anus (F
i
gure 18.7A). T
h
ey commun
i
cate w
i
t
h
t
h
e
h
emocoe
l
an
d
are we
ll

supp
li
e
d
w
i
t
h
t
racheae. Their walls are a one-cell-thick syncytium (perhaps an adaptation to eliminate
i
ntercellular leakage) and covered with a thin cuticle (Figure 18.7B). Mosquito larvae ca
n
accumulate chloride, sodium,
p
otassium, and
p
hos
p
hate ions a
g
ainst lar
g
e concentratio
n
g
ra
di
ents us
i

n
g
t
h
e
p
a
pill
ae. T
h
ea
bili
t
y
to accumu
l
ate
i
ons var
i
es w
i
t
h
t
h
e
h
a
bi

tat
i
nw
hi
c
h
an
i
nsect
i
s norma
lly f
oun
d
.T
h
us, Culex
p
i
p
ien
s
,
w
hi
c
hi
s
f
oun

di
n contam
i
nate
d
water
,i
s
l
ess e
f
fic
i
ent at co
ll
ect
i
ng
i
ons t
h
an
A
e
d
es aegypti
,
w
hi
c

h
typ
i
ca
ll
y
li
ves
i
n
f
res
h
ra
i
nwater
pools. Indeed, normal larvae of the latter species can maintain a constant hemolymph sodium
concentration when the sodium concentration of the external medium is onl
y6
µ
M/
l. Th
e
h
emol
y
m
p
h sodium concentration under these conditions is onl
y

about 5% below the norma
l
l
eve
l
(S
h
aw an
d
Sto
bb
art, 19
6
3).
4
.3. Brackish-Water and Saltwater Insect
s
Brac
ki
s
h
water may
b
e
d
efine
d
as water w
h
ose osmot

i
c concentrat
i
on
i
s
i
nt
h
e range
3
00 mOsm (about 1.1% sodium chloride) (the osmotic concentration of the hemolymph) t
o
1000 mOsm
(
about 3.
5
% sodium chloride
)(
the concentration of normal seawater
)
, with sal
t
w
ater havin
g
osmotic concentrations
g
reater than those of natural seawater. The definitions
5

52
C
HAPTER
18
F
IGURE 18.7. (A) Poster
i
or en
d
o
f
A
edes aegypti to s
h
ow ana
l
pap
ill
ae; an
d
(B) structura
ld
eta
il
so
f
as
i
ng
l

e
anal
p
a
p
illa. [A, after V. B. Wi
gg
lesworth, 196
5
, T
h
e Princip
l
es o
f
Insect P
hy
sio
l
og
y
,6
t
h
e
d
., Met
h
uen an
d

Co. B
y
p
ermission of the author. B, after V. B. Wi
gg
lesworth, 1933, The effect of salts on the anal
g
lands of the mos
q
uito
l
arva
,
J
.
Exp. Biol.
10
:1–15. By permission of Cambridge University Press.
]
are not entirely arbitrary, as they tend to describe habitats occupied by particular species. Fo
r
example, larvae of the mosquit
o
C
u
l
iseta inornat
a
a
re found in a variety of brackish waters,

includin
g
tidal estuaries and some inland
p
onds, but cannot survive in natural seawater.
In contrast
,l
arvae o
f
A
edes taeniorh
y
nchus
,
w
hi
c
h
occur
i
n coasta
l
sa
l
t mars
h
es
,h
ave a
max

i
mum sa
li
ne to
l
erance equ
i
va
l
ent to 10% so
di
um c
hl
or
id
e. Even more remar
k
a
bl
e are
l
arvae of Ep
h
y
d
ra cinere
a
t
hat are found in the Great Salt Lake of Utah where the salinity may
exceed the equivalent of 20% sodium chloride (i.e., about six times that of normal seawater).

T
he habitat occu
p
ied b
y
brackish-water and saltwater insects can var
y
widel
y
in ioni
c
c
ontent an
d
osmot
i
c
p
ressure. Dur
i
n
gp
er
i
o
d
so
f
warm,
d

r
y
weat
h
er t
h
esa
li
n
i
t
y
ma
yi
ncrease
severa
lf
o
ld
. Converse
ly
,a
f
ter
h
eav
y
ra
i
ns or t

h
eme
l
t
i
n
g
o
f
snow
i
ns
p
r
i
n
g
,t
h
esa
li
n
i
t
y
ma
y
approach that of fresh water. It is not surprising, therefore, to find experimentally that such
insects can regulate their hemolymph osmotic pressure over a wide range of external salt
c

oncentrations (Fi
g
ure 18.8). Larvae of Ae
d
es
d
etritu
s
an
d
E
p
hyd
ra ripari
a
,
inhabitants of
sa
l
t mars
h
es, can surv
i
ve
i
nme
di
a conta
i
n

i
n
g
t
h
ee
q
u
i
va
l
ent o
f
0toa
b
out 7–8% so
di
u
m
chl
or
id
e. Over t
hi
s ran
g
eo
f
concentrat
i

ons t
h
e
h
emo
ly
m
ph
osmot
i
c
p
ressure c
h
an
g
es
by
o
n
l
y 40–
6
0%
.
When their external medium is dilute (i.e., its osmotic pressure is less than that of
the hemolymph), both brackish-water and saltwater insects osmoregulate to keep their
55
3
N

ITR
O
GEN
O
U
S
EXCRETION
A
ND
S
ALT AND
WA
TER BALANC
E
F
IGURE 18.8. T
h
ere
l
at
i
ons
hi
p
b
etween osmot
i
c pressure o
f
t

h
e
h
emo
l
ymp
h
an
d
t
h
at o
f
t
h
e externa
l
me
di
um
i
n
s
ome sa
l
twater
(
sw
)
an

db
rac
ki
s
h
-water
(b
w
)l
arvae. [A
f
ter J. S
h
aw an
d
R. H. Sto
bb
art, 19
6
3, Osmot
i
can
di
on
i
c
r
egulation in insects, Adv. Insect Physiol
.
1

:
315–399. By permission of Academic Press Ltd. and the authors.
]
h
emo
ly
m
ph
osmot
i
c
p
ressure more or
l
ess constant. L
ik
e
f
res
h
water s
p
ec
i
es, t
h
e
yp
ro
d

uc
e
dil
ute ur
i
ne an
d
act
i
ve
ly
resor
b
sa
l
ts t
h
rou
gh
t
h
e recta
l
wa
ll
. Mos
q
u
i
toes

f
rom t
h
ese
h
a
bi
tats
m
ay a
l
so ta
k
eup
i
ons v
i
at
h
e ana
l
pap
ill
ae. However, w
h
en t
h
e externa
l
osmot

i
c pressure
r
ises above that of the hemolymph, leading to loss of water from the body by osmosis
,
saltwater and brackish-water species employ different strategies
.
S
a
l
twater mos
q
u
i
toes, on w
hi
c
h
most ex
p
er
i
menta
l
wor
kh
as
b
een
d

one, counteract
th
e
l
oss o
f
water
by d
r
i
n
ki
n
g
t
h
e externa
l
me
di
um;
f
or exam
pl
e
,
A
.
t
aeniorh

y
nchus
la
r
vae
i
ngest 240% o
f
t
h
e
i
r
b
o
d
ywe
i
g
h
t per
d
ay (Bra
dl
ey, 1987). T
h
e water ta
k
en
i

n, an
d
t
h
e
i
ons
i
t
contains, are then absorbed across the midgut wall, a process that may serve to concentrate
food in the midgut prior to digestion (Phillip
s
e
ta
l.
, 1978). Thus, the problem for thes
e
i
nsects is to rid themselves of the excess ions that enter the hemol
y
m
p
h. As in insects from
ot
h
er
h
a
bi
tats, t

h
eMa
lpighi
an tu
b
u
l
es
p
ro
d
uce a
p
otass
i
um-r
i
c
hfl
u
id i
sosmot
i
cw
i
t
h
t
he
h

emo
ly
m
ph
,an
d
t
h
e
i
rma
i
n
f
unct
i
on a
pp
ears to
b
et
h
e secret
i
on o
f
su
lf
ate. Format
i

on o
f
h
yperosmotic urine occurs as a result of active secretion of ions across the wall of the rectum
,
w
hich in these species is divided into anterior and posterior segments (Figure 18.9). Th
e
p
osterior se
g
ment a
pp
ears to be the more im
p
ortant, secretin
g
sodium, chloride, ma
g
nesium
,
a
n
dp
otass
i
um
i
ons
i

nto t
h
e recta
ll
umen. T
h
ero
l
eo
f
t
h
e anter
i
or se
g
ment
i
s
l
ess c
l
ear,
th
ou
gh
exc
h
an
g

eo
fbi
car
b
onate
f
or c
hl
or
id
e
i
ons occurs
h
ere, as ma
y
t
h
e resor
p
t
i
on o
f
se
l
ecte
di
norgan
i

can
d
organ
i
cso
l
utes (espec
i
a
ll
y
i
n
l
arvae
i
n
dil
ute me
di
a). As a resu
l
to
f
t
hese activities, saltwater mosquitoes are able to strongly regulate their hemolymph osmoti
c
p
ressure and ionic content over a wide ran
g

e of external concentrations (Fi
g
ure 18.8)
.
I
n contrast to sa
l
twater
f
orms
,b
rac
ki
s
h
-water
i
nsects
b
ecome osmocon
f
ormers
i
nex
-
t
erna
l
me
di

a more concentrate
d
t
h
an t
h
e
i
r
h
emo
ly
m
ph
;t
h
at
i
s, t
h
e
i
r
h
emo
ly
m
ph
osmot
i

c
pressure
i
ncreases approx
i
mate
l
y para
ll
e
l
w
i
t
h
t
h
at o
f
t
h
e surroun
di
ng me
di
um (F
i
gure
18.8). Unlike the situation in freshwater species, however, where osmoconformation is
largely because of increases in hemolymph inorganic ion levels (mainly those of sodiu

m
5
5
4
C
HAPTER
18
F
I
G
URE 18
.
9
.
E
xcretor
y
s
y
stem of saltwater mos
q
uito larvae. Known
p
athwa
y
s of active ion trans
p
ort are
shown. AR, anterior rectal segment; MG, midgut; MT, Malpighian tubule; PR, posterior rectal segment. [After
T

.
J
. Bra
dl
e
y
, 1987, P
hy
s
i
o
l
o
gy
o
f
osmore
g
u
l
at
i
on
i
n mos
q
u
i
toes
,

Annu. Rev. Entomo
l
.
32
:
439–4
6
2. Re
p
ro
d
uce
d
,
w
ith
p
ermission, from the Annual Review of Entomolo
gy
, Volume 32

c
1
987 b
y
Annual Reviews, Inc.]
and chloride), in brackish-water species the hemolymph inorganic ion levels remain mor
e
o
r less constant and the increased osmotic

p
ressure is the result of the addition of or
g
ani
c
c
om
p
onents.
In
Culex tarsali
s
l
arvae acc
li
mate
d
to
6
00 mOsm seawater,
f
or exam
pl
e, t
h
e
c
oncentrat
i
ons o

f
am
i
no ac
id
s (es
p
ec
i
a
lly p
ro
li
ne an
d
ser
i
ne) an
d
tre
h
a
l
ose were severa
l
f
old greater than those of insects acclimated to
5
0 mOsm seawater (Bradley, 1987). The use
o

f these molecules to prevent osmotic dehydration is interesting in view of their somewha
t
p
arallel role as cryoprotectants in cold-hardy insects (Chapter 22, Section 2.4.1).
5.
Hormonal Contro
l
As in other systems with a homeostatic role, the activities of the excretory system
,
including both production of nitrogenous waste and osmoregulation, need to be regulate
d
to suit the s
p
ecific but chan
g
in
g
re
q
uirements of the insect. This coordination is effected b
y
h
ormones
.
Th
oug
h
t
h
ere

i
s strong c
i
rcumstant
i
a
l
ev
id
ence
f
or
i
nvo
l
vement o
fh
ormones
i
nt
he
synthesis of uric acid, neither the nature of the factor(s) involved nor the site of action is
k
nown. Changes in the rate of uric acid production, for example, occur at specific stages
in an insect’s life and these can be correlated with fluctuations in the levels of
j
uvenile
h
ormone an
d

ec
dy
stero
id
s. S
i
m
il
ar
ly
, remova
l
o
f
t
h
e cor
p
ora a
ll
ata or cor
p
ora car
di
aca ma
y
mar
k
e
dly

a
ff
ect ur
i
cac
id p
ro
d
uct
i
on t
h
ou
gh
,a
g
a
i
n,
i
t
i
s uncerta
i
nw
h
et
h
er t
h

e res
p
onse
is
direct or indirect, for example, via an influence on amino acid or protein metabolism.
In contrast, the occurrence of both diuretic and antidiuretic hormones is firmly estab
-
l
ished (Philli
p
s, 1983; S
p
rin
g
, 1990; Coast, 1998a, 2001; G¨ade, 2004). In most s
p
ecies,
neurosecretor
y
ce
ll
s
i
nt
h
e
b
ra
i
n

p
ro
d
uce t
h
ese
h
ormones t
h
at are t
h
en store
di
nt
h
e cor
p
ora
c
ar
di
aca, t
h
ou
gh
t
h
ere are man
y
re

p
orts o
fdi
ures
i
s-mo
difyi
n
gf
actors
i
n extracts
f
rom ot
h
er
gang
li
a
i
nt
h
e ventra
l
nerve cor
d
.A
l
most a
ll id

ent
i
fie
d
osmoregu
l
atory
h
ormones are pep
-
tides, though in some insects (e.g.
,
Rh
o
d
niu
s
,
locusts and crickets) serotonin also appear
s
to be an im
p
ortant diuretic factor
.
One or more
di
uret
i
c
h

ormones are re
l
ease
d
a
f
ter
f
ee
di
n
gi
n man
y
terrestr
i
a
li
nsects.
In
Rh
o
dniu
s
,w
hi
c
h
ta
k

es
i
nterm
i
ttent
l
ar
g
e
bl
oo
d
mea
l
s, stretc
hi
n
g
o
f
t
h
ea
bd
om
i
na
l
wa
ll

b
r
i
ngs a
b
out
h
ormone re
l
ease (Ma
dd
re
ll
,19
6
4). In
S
c
h
istocerca, Dys
d
ercu
s
,
an
d
ot
h
e
r

insects that feed more or less continuously, it is probably the stretching of the foregut tha
t
c
auses release of hormone (Mordue, 1969; Berridge, 1966). Diuretic hormones appear to
555
N
ITR
O
GEN
O
U
S
EXCRETION
A
ND
S
ALT AND
WA
TER BALANC
E
act primarily on the Malpighian tubules, stimulating them to secrete potassium ions at
a
g
reater rate, thereb
y
creatin
g
an enhanced flow of water across the tubule wall (Pilcher
,
1970). T

hi
s
p
r
i
mar
y
act
i
on o
fdi
uret
i
c
h
ormone w
ill
a
ff
ect
b
ot
h
osmore
g
u
l
at
i
on an

d
t
h
e
e
xcret
i
on o
f
ur
i
cac
id
. In some
i
nsects,
f
or exam
pl
e Calli
p
hora
a
n
d
S
chistocerc
a
,di
uret

ic
h
ormone
h
as a
d
ua
l
act
i
on, caus
i
ng acce
l
erate
d
secret
i
on t
h
roug
h
t
h
etu
b
u
l
es an
d

as
l
ow
i
ng
d
own of water resorption through the rectal wall. In
Rh
o
d
niu
s
an
d
other insects that have
t
wo diuretic factors, it is believed that these work s
y
ner
g
isticall
y
so that a small chan
g
ein
th
e amount o
f
e
i

t
h
er w
ill i
n
d
uce a
l
ar
g
ec
h
an
g
e
i
nt
h
e rate o
fp
ro
d
uct
i
on o
f
t
h
e
p

r
i
mar
y
fl
u
id
.Inot
h
er wor
d
s, t
hi
s arran
g
ement en
d
ows t
h
e excretor
y
s
y
stem w
i
t
hg
reat sens
i
t

i
v
i
t
y
,
e
na
bli
ng t
h
eMa
l
p
i
g
hi
an tu
b
u
l
es to react qu
i
c
kl
ytoc
h
anges
i
n water

l
oa
d
w
i
t
hi
nt
h
e
b
o
d
y.
A
n ancillary effect of diuretic peptides and serotonin is to stimulate contraction o
f
t
he muscles on the outside of the tubules, enhancing their writhing movements. This will
r
e
d
uce t
h
et
hi
c
k
ness o
f

t
h
e unst
i
rre
dl
a
y
er o
fh
emo
ly
m
ph
a
dj
acent to t
h
etu
b
u
l
e, as we
ll
a
s
i
m
p
rov

i
n
gfl
u
id fl
ow w
i
t
hi
nt
h
etu
b
u
l
e (Coast, 1998
b
).
T
h
e nature an
d
mo
d
eo
f
act
i
on o
f

ant
idi
uret
i
c
f
actors are
l
ess we
ll
un
d
erstoo
d,
an
d
u
ntil recently it was thought that they act only at the level of the rectum, enhancing fluid
u
ptake. One possible means of achieving this would be through stimulation of ion secretio
n
a
s
p
ro
p
osed in the scheme for water resor
p
tion outlined earlier (Fi
g

ure 18.5). A chlorid
e
t
rans
p
ort-st
i
mu
l
at
i
n
gp
e
p
t
id
e (CTSP) (mo
l
ecu
l
ar we
igh
t 8000)
i
so
l
ate
df
rom t

h
e cor
p
or
a
car
di
aca o
f
Schistocerc
a
s
t
i
mu
l
ates resorpt
i
on o
f
t
h
ese
i
ons
f
rom t
h
e recta
ll

umen (Spr
i
ng
,
1990; Phillips and Audsley, 199
5
), but whether it promotes water resorption has not been
d
etermined. Curiously, a second peptide (ion transport peptide [ITP]) from the same sourc
e
a
nd havin
g
a similar molecular wei
g
ht (8500) has been identified (Philli
p
s
e
ta
l
.
, 1998)
.IT
P
al
so st
i
mu
l

ates c
hl
or
id
e
i
on resor
p
t
i
on,
b
ut
i
nt
h
e
il
eum, an
d
t
h
e consensus
i
st
h
at t
h
e
y

ar
e
diff
erent
h
ormones
.
Fo
ra
f
ew
i
nsects,
i
nc
l
u
di
ng
Rhod
niu
s
a
n
d
T
ene
b
ri
o

,
t
h
e ant
idi
uret
i
c
h
ormone acts o
n
t
he Malpighian tubules, inhibiting the active transport of potassium ions across the tubule
wall (Ei
g
enhee
r
et a
l.
,
2002)
.
Af
urt
h
er as
p
ect o
fh
ormona

l
contro
li
st
h
at some
i
nsects
p
ro
d
uce
b
ot
hdi
uret
i
can
d
a
nt
idi
uret
i
c
h
ormones s
i
mu
l

taneous
ly
a
f
ter
f
ee
di
n
g
,anact
i
on t
h
at ma
y
a
pp
ear to
b
e coun-
t
erpro
d
uct
i
ve. Proux
e
t al. (1984) suggeste
d

,
h
owever, t
h
at t
hi
s act
i
on may en
h
ance
fl
u
id
cycling to clear metabolic wastes from the hemolymph.
Because, presumably, there is a direct relationship between the amount of food con-
sumed, the amount of hormone released, and the
q
uantit
y
of water removed across the
t
u
b
u
l
es or resor
b
e
df

rom t
h
e recta
ll
umen,
i
t
i
s
dif
ficu
l
ttosee
h
ow suc
h
as
i
m
pl
e arran
g
e-
me
n
t will wo
r
k othe
r
tha

n
i
n
i
n
sects such as
R
h
o
dniu
s
wh
ose
f
oo
dh
as a constant wate
r
content. The physical stimulus of “stretching” alone would not provide a precise enoug
h
m
echanism for water regulation in insects whose food differs in water content. Some other
control s
y
stem must therefore o
p
erate. Perha
p
s an insect can monitor the water content of it
s

f
oo
d
or, a
l
ternat
i
ve
ly
,t
h
e resor
p
t
i
ve
p
ower o
f
t
h
e recta
l
wa
ll
ma
yb
e contro
ll
e

ddi
rect
ly by
th
e
h
emo
ly
m
ph i
tse
lf
.P
hillip
s (19
6
4
b
)s
h
owe
d
t
h
at t
h
e rate at w
hi
c
h

so
di
um an
dp
otass
i
um
i
ons are resorbed is dependent on the ionic concentration of the hemolymph.
Very little work has been done on the hormonal control of salt and water balance in
aq
uatic insects. However, as a result of his ex
p
eriments on Ae
d
es aeg
y
pti
,
Stobbart
(
1971
)
su
gg
este
d
t
h
at accumu

l
at
i
on o
f
so
di
um
i
ons across t
h
ewa
ll
o
f
t
h
e ana
lp
a
pill
ae
i
sun
d
er
e
n
d
ocr

i
ne contro
l
.Int
h
e water
b
oatman
,
Cenocorixa blaisdell
i
,an
dl
arvae o
f
t
h
e
d
ra
g
on
fly
,
L
ibe
ll
u
l
a

q
ua
d
rimacu
l
at
a
,e
xtracts o
f
t
h
e
h
ea
d
an
d
t
h
orac
i
c gang
li
a, respect
i
ve
l
y, st
i

mu
l
at
e
Malpighian tubule secretion (Spring, 1990).
5
5
6
C
HAPTER
18
6
. Summar
y
T
he removal of nitrogenous wastes and maintenance of a suitable hemolymph salt and
w
ater content are two closely linked processes. In most insects, the predominant nitrogenous
w
aste
i
sur
i
cac
id
,w
hi
c
hi
s remove

df
rom t
h
e
h
emo
ly
m
ph
v
i
at
h
eMa
lpighi
an tu
b
u
l
es as t
h
e
so
l
u
bl
eso
di
um or
p

otass
i
um sa
l
t. Prec
ipi
tat
i
on o
f
ur
i
cac
id
occurs usua
lly i
nt
h
e rectum a
s
a resu
l
to
f
resorpt
i
on o
fi
ons an
d

water
f
rom, an
d
ac
idi
ficat
i
on o
f
,t
h
eur
i
ne. A
ll
anto
i
nan
d
allantoic acid are excreted in quantity by some insects and may be the major nitrogenou
s
w
aste. Urea is of little significance as a waste product, and ammonia is generally produced
o
nl
y
in a
q
uatic s

p
ecies.
Insects are usua
lly
a
bl
etore
g
u
l
ate t
h
esa
l
tan
d
water content o
f
t
h
e
h
emo
ly
m
ph
w
i
t
hin

narrow
li
m
i
ts. In a
ll i
nsects, a pr
i
mary excretory
fl
u
id
,
i
sosmot
i
cw
i
t
hh
emo
l
ymp
hb
ut
dif
-
f
ering in ionic composition, is produced in the Malpighian tubules. Production of tubul
e

fl
uid is driven by active transport of potassium ions. When this fluid reaches the poste-
rior rectum, it is modified accordin
g
to an insect’s needs. In terrestrial insects selective
resor
p
t
i
on o
fi
ons an
d/
or water occurs. Fres
h
water s
p
ec
i
es osmore
g
u
l
ate
by p
ro
d
uc
i
n

g hy-
p
oosmot
i
cur
i
ne
f
rom w
hi
c
h
use
f
u
l
mater
i
a
l
s
h
ave
b
een resor
b
e
d
.Ina
h

yperosmot
i
cme
di
um
they become osmoconformers, their hemolymph osmotic pressure paralleling that of the
medium. Brackish-water and saltwater insects have excellent ability to osmoregulate ove
r
a wide ran
g
e of environmental conditions. In dilute media the
y
behave much like freshwa-
ter s
p
ec
i
es,
f
orm
i
n
g hyp
oosmot
i
cur
i
ne an
d
resor

bi
n
g
use
f
u
l
com
p
onents. In me
di
aw
i
t
h
o
smot
i
c pressures greater t
h
an t
h
at o
fh
emo
l
ymp
h
,sa
l

twater spec
i
es
d
r
i
n
k
excess
i
ve
l
yan
d
p
roduce hyperosmotic urine by secreting ions across the rectal wall; in contrast, brackish
-
w
ater insects osmoconform by increasing the concentration of amino acids and trehalose
in the hemol
y
m
p
h
.
B
ot
hdi
uret
i

can
d
ant
idi
uret
i
c
h
ormones are
k
nown. T
h
e
f
ormer st
i
mu
l
ate Ma
lpighi
an
tu
b
u
l
e
fl
u
id p
ro

d
uct
i
on an
d
ma
yi
n
hibi
t water resor
p
t
i
on
f
rom t
h
e rectum; ant
idi
uret
i
c
hormones mostly appear to act only by stimulating water resorption from the rectal lumen;
however, in a few species the antidiuretic factor inhibits potassium ion transport (henc
e
f
ormation of the
p
rimar
y

excretor
y
fluid) in the Mal
p
i
g
hian tubule.
7.
Literat
u
r
e
F
or
a
dditional information, see Maddrell
(
1971, 1980
)
, Stobbart and Shaw
(
1974
)
,
P
hilli
p
s (1981), and Bradle
y
(1985) [

g
eneral]; Bursell (1967) and Cochran (1975, 1985
)
[
n
i
tro
g
enous waste excret
i
on]; an
d
P
hillip
s (1977) [sa
l
tan
d
water
b
a
l
ance]. Hormona
l
regu
l
at
i
on o
f

excret
i
on
i
s cons
id
ere
db
yP
hilli
ps (1983), Spr
i
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hilli
ps an
d
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58
C
HAPTER
18
R
amsa
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.
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f
so
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