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Digestive,
Excretory, &
Endocrine Systems
DIGESTION
Main Points:
• General morphology: mouthparts, esophagus, crop,
proventriculus, midgut, gastric cecae, hindgut, rectum
•Adaptations for digestion depend on type of food eaten.
• Salivary glands aid ingestion/digestion in various ways.
• Special adaptations include filter chamber (water shunt),
symbiotic microorganisms.
pyloris
from Gullen & Cranston 2000
Digestive and excretory organs
of a typical terrestrial vegetarian
insect.
Digestive system & functions.
from Evans 1984
EXCRETION
Main Points:
• Excretory adaptations driven interactively by:
1) nitrogenous waste elimination &
2) water conservation.
• Waste elimination relies on active ion transport and
osmosis.
• Most important organs of elimination are Malpighian
tubules & rectum.
• Main molecule of nitrogenous excretion = uric acid (but
exceptions).
more water
more energy
uric acid
most insects
ammonia
urea
aquatic insects
vertebrates
Trade-offs in energy vs. water required in synthesis in
different nitrogenous waste molecules.
Malpighian
tubule
from Evans 1984
Excretory organs & functions. As in nutrient absorption, the complex process
utilizes diffusion gradients, osmosis, active ion transport, and pH changes.
Malpighian tubule X-sec.
Major organs and primary
functions of typical terrestrial
insect excretory system.
from Gullen & Cranston 2000
Malpighian tubule X-sec.
Showing nuclei (outlined)
of 2 adjacent cells.
from Evans 1984
Single layer structure
of Malpighian tubule.
Structure of rectum.
from Gullen & Cranston 2000
Nonterrestrial &
Atypical Systems
Aquatic species
May excrete ammonia
May have “chloride cells”
(osmoregulation)
dragonfly nymph
Blood feeders
food: high-N, high water
horse fly
Plant Vascular Feeders
May have a “filter chamber”
shunt
aphid
(proteins, etc.)
from Gullen & Cranston 2000
(water & sugars)
Adult female mosquitoes also face an excess
Diagram of the water
filterwaste
chamber,
modification
of the digestive
problemaafter
taking a blood
meal but
not have
a filter
chamber.
Why the midgut.
system that functions
todoshunt
excess
water
around
would a filter chamber not be necessary?
Fat body, a diffuse organ
with multiple functions:
1)
2)
3)
4)
Carbohydrate & lipid
metabolism
Storage of glycogen, fat,
& protein
Synthesis of blood
proteins
Regulation of blood
sugars
Cell types:
1)
2)
Fat tissue, oenocytes,
and nephrocytes
from Snodgrass 1935
3)
4)
5)
Urocytes, waste storage
Trophocytes, many
functions
Mycetocytes, symbionts
Oenocytes
Nephrocytes
Endocrine System
Main Points:
•Hormonal control is vital to many aspects of insect physiology
& behavior, including: development, molting, & reproduction.
• Major hormonal centers include the brain, corpora allata,
corpora cardiaca, prothoracic gland.
• There are dozens of known insect hormones.
• Best known system = “the Triumvirate” of
1) neurohormones, 2) ecdysteroids, & 3) juvenile hormones.
• Some insect hormone analogs are used as pesticides.
•Legacy insect hormone research at UW
=> PTTH pro-thoracico-tropic-hormone
PTTH (storage)
=> JH juvenile hormone
=> Ecdysone (ecdysteroids)
from Gulen & Cranston 2000
Important aspects of the typical insect endocrine system.
Major Insect Hormone Types
Neurohormones
(peptides)
Most diverse class
Regulate various developmental
and metabolic processes
Modes of action:
Along nerve axons
Through haemolymph
(carrier proteins)
Indirect: through effects on
other glands
Ecdysteroids
(sterols, from diet)
Primarily ß-ecdysone.
Molt-promoting but
many other functions.
ß-ecdysone
Juvenile Hormones
(sesquiterpenes)
Several forms, sometimes >1
produced by same species
Functions:
Control of metamorphosis
Retention of larval characteristics
Inhibition of metamorphosis
Regulation of reproduction
Stimulation of egg yolk deposition in
ovary of mother
Controls accessory gland activity
Controls production of pheromones
Historical Perspective
Demonstrated
involvement of
hormone from
anterior body &
timing of release.
Confirmed
location of
hormone in brain.
from Evans 1984
Kopec’s simple ligation & debraining experiments (ca. 1919).
Insect Hormone Research Legacy
Kopeć (Poland, demonstrated PTTH)
Williams (Harvard,
Riddiford [& Truman]
conditioning via
environment, prothoracic
(recently active at UW, JH
functions in molting, development;
other aspects)
gland target)
Fukuda (U. Tokyo,
Gilbert (UNC, neurosecretory cells)
importance of prothoracic
gland)
Wigglesworth
Edwards (emeritus at UW, insect
(Oxford, confirmed
Kopec’s work,
connection with molting,
timing of release)
glia, other neurobiological aspects)
COLOR
Sources of Color in Insects
1) Incidental
e.g. internal organs, haemolymph, transparent cuticle.
2) Pigments
endogenous metabolic sources, sequestered from plant
host, microbial endosymbionts.
3) Physical (cuticular surface quality) interference,
scattering.
Microstructure of a butterfly
wing scale.
In many species: a teneral or callow state occurs immediately
after molting, before cuticle tans and pigments are deposited.
X-sec
Insect Wings Identical basic veination pattern in all winged
insects indicates a single origin
APTERYGOTA
PTERYGOTA
Predominance of
wings in insects.
a firebrat (THYSANURA), a primitive apterygote
“PALEOPTERA”
NEOPTERA
Modern vs. ancient wings
ODONATA
“EXOPTERYGOTA”
Prevalence of holometaboly
and highly advanced wings
ENDOPTERYGOTA
(~85% of species)
THYSANOPTERA
H
E
M
I
P
T
E
R
A
LEPIDOPTERA
L
E
P
I
D
O
P
T
E
R
A
HYMENOPTERA
COLEOPTERA
DIPTERA
DIPTERA
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