ENTM 340 Insect Pests of Trees Turf and Ornamentals
C. Sadof Purdue University
Internal Insect Anatomy
- In this
lecture we will cover the following insect systems to give you an
appreciation for how insects perform critical body functions. As you study this material pay
particular reference to how this information can be used to find a weak
link that can be targeted by insecticides. Use the handouts and the
laboratory exercises to learn the system.
Consumption and processing of food
system- movement of body fluids.
system - breathing
system – enervation of muscles, and production of neurohoromones
System- (Figure 3.13 Gullon and Cranston)
by epithelial wall of cells that is one cell thick and surrounded by
muscles that help move food through gut.
Foregut and Hindgut are lined with cuticle. Midgut, due
its role in nutrient absorption is not lined. Gut pH will vary with insects. The
effect of pH on the chemistry food and tends to influence kind of food
insects by altering the effects of the poisons that plants produce to
defend themselves against insects.
Ingestion, Storage, grinding and transport of food to midgut
goes from mouth through pharynx and oesophagus where it is
stored in the crop until it is
ground by the proventriculus. Paired salivary glands at the anterior of the foregut function to
produce saliva that aids digestion, prevents clotting in animal and plant
tissue, or produce silk in caterpillars.
- Midgut- Biochemical breakdown (digestion
via secretion of enzymes) and nutrient absorption-, Remaining
material enters the hindgut.
passes through ventriculus
that lines the food bolus with a fine chitin/carbohydrate/protein mesh
called the peritrophic membrane. This allows digestion
of food bolus, while protecting the epithelial cells from injury by sharp
food. (See Figure 3.16. Gullon and Cranston)
- Bacillus thuringiensis,
a common biological insecticide, kills insects by ripping holes in the peritrophic membrane of the midgut and damaging this fine epithelial wall.
ceacae increase the surface area available for
short gut for rapid throughput feeders on solid food like caterpillars (GM).
convoluted gut (filter chamber) for liquid feeders like aphids, to
maximize absorption. Hemiptera do not produce peritrophic
Absorption of water, salts and other important minerals, elimination of
feces through anus. Like many animals, water regulation is critical to its
conservation… Most insects need to conserve. (See Fig 3.17 Gullon
and Cranston for Schematic).
- Malpighian tubules filter nongaseous wastes from haemolymph. Urine is excreted from tubules into the
anterior portion of the hindgut.
- Adaptations: Cryptonephridia
tubules are enclosed in a perirectal space and
in a common trunk to conserve water and resorb
it from relative humidity. This is
useful for insects adapted to dry conditions. (Oseto p. 53).
Structure and Function. Insects have an open circulatory system that
moves body fluids around insects bodies. (Figure 3.9 Gullon and Cranston).
Circulation of provides nutrients and oxygen to body tissues, and extracts
metabolic waste through the tendrils of the Malpighian
tubules. Insecticides that attack insect
nervous systems disrupt the muscles that cause fluid circulation.
Dorsal vessel – Open ended at the head, and closed at
the tail end, this functional insect heart is supported by alary muscles. Waves of contraction pumps
fluid toward head. Ostioles are pairs of holes in each segment that via the aid of one-way
valves allows hemolymph (=insect blood) to be sucked into the
vessel with each contraction.
Ventral diaphragm- Located above the ventral nerve
chord acts in concert with thoracic pulsatile organs to pump blood from the head to the
tail of the insect.
never see an insect panting like a dog.
They don’t breath through their mouths. Rather, they breathe through a pair of
holes called spiracles at the
side wall (pleuron) of each segment. Smothering agents, like insecticidal
soap or oil will clog spiracles. Neurotoxins disable coordinated
contractions that facilitate ventilation.
moves through the spiracles though a network vacuum hose like pipes called
a tracheal system (Oseto p.
55-56). Air moves along a main ventral trunk to smaller pipes
called tracheoles. These tracheoles are embedded
into muscle tissue to faciliate the inward diffusion
of oxygen and outward diffusion of CO2.
of the tracheoles is enhanced by active
contraction of thoracic muscles.
Most insects have an open respiratory system that allows direct exchange
of oxygen from atmosphere. Aquatic
insects and internal parasites that live inside the body of other insects
have a closed system that require a gill like
apparatus to extract oxygen. Other adaptions for
very small soil dwelling insects like Collembolla,
other animals, insects transmit signals from sensory organs to central
processing centers or ganglia.
These ganglia send signals to muscles and cause them to
contract. They have reflex arcs,
like humans that bypass the insect brain. Ganglia are connected along a
ventral nerve chord below the digestive tract. Insect brains are fused ganglia in the
head. (See Oseto page 60). Compounds used to transmit nerve
impulses and innervate mammalian muscle contraction perform the same
functions in insects. Insecticides
that target nervous and muscular signal transfer can also be toxic to
Reproductive organs. (Figure 3.20 Gullan and Cranston,
- Ovarioles, produce oocytes
are dropped down from the calyx end of the ovaioles
into the oviducts where they may be fertilized as they pass through the
females have an organ (spermatheca) to store and
maintain sperm after mating
produce sperm that pass through the ejaculatory duct through the intromittent organ.
is deposited with other nutrients into the female genital chamber.
deposited by males are often resorbed by females
and used to help mature oocytes
Kinds of Reproduction
reproduce sexually or asexually via a process known as parthenogenisis. Some insects like aphids, will
vary in how they reproduce, reproducing asexually at some times of year and sexually at others. Some
species, most notably many wasps, have a haplodiploid chromosome system that allows
them to control the sex of their offspring. Males wasps are
produced by unfertilized eggs. Female wasps are produced by fertilized
eggs. In other species, like black vine weevils a pest of nursery
containers, males are unknown. Some
insects like certain aphids give birth to live young (viviparous), others
lay eggs (oviparous). Some eggs
produce individual offspring, other eggs divide multiple times to produce
50 or more clones in a process called polyembryony.
insects need use chemical scents to find each other over long distances.
Called sex pheromones, these
scents are secreted by females to attract potential mates who reside
downwind. Traps, baited with these
materials are often used monitor insect populations. In these cases males
have special feathery antenna to allow them to detect the minute
quantities of scent they use to follow the plume of pheromone to its
control of Insect Systems (Oseto p 78)
All insects grow by molting from
immature to more mature forms. The
molting process and the rate of maturation during each molt is
controlled by two broad classes of hormones that are produced by glands in the
brain and the prothorax.
stimulate the molting process to commence and stimulate maturation.
- Juvenile hormones act to counter
the activity of ecdysone, delaying moulting and maturation.
- The ratio of these 2 compounds
determines the level of maturity of the insect during the next molt.
- Neuropeptides, secreted by glands in the brain, are
protein messengers that regulate many of the systems critical to insect
development, homeostatis, metabolism and
In the 1980’s a new group of
insecticides called insect growth regulators
have been developed. These materials
alter the delicate balance of these hormones and neuropeptides
that kill insects during the moulting process or sterilize
them. Advances in molecular biology in the late 90’s have greatly honed the
ability to identify specific peptides and map their genes will be producing a
wide range of safer insecticides in the near future.
Gullan, P.J. and P. S. Cranston
insects. An outline of entomology. Blackwell
Science, Incorporated. Malden, MA.
the function of the foregut. Besure to include the role of the proventriculus
and the salivary glands.
is a peritrophic membrane and how does it protect the
midgut? How is
this membrane affected by the biological insecticide Bacillus thuringiensis.?
is the relationship between the morphology of the gastric cecae
and absorbtion of nutrients?
to liquid feeders (sap feeders) modify the gut to allow them to absorb
is similar between the function of human kidneys and Malpighian
humans, insects have an open circulatory system. How does the insect pump its haemolymph and where does it flow?
do not have lungs. What kind of respiratory system do they have?
insects do not have respiratory pigments like haemoglobin. How do they move oxygen to the muscle tissue?
is a spermathecae and what is its relation to
fertilization of eggs.
10. Wasps are parthenogenetic, with fertilized eggs becoming females and
unfertilized eggs becoming males. Given what you just learned about spermathecae how can female wasps determine the sex of
11. What is a
12. What are
the names of the two kinds of insect hormones that control moulting?
How does this relate to the development of new insecticides.