1. INSECT INTERNAL ANATOMY
Unit 3 - Internal Features of Insects
INSECT INTERNAL ANATOMY
ENT063 - Spring 2006

2. Major Internal Systems of the Insect Body
Respiration Reproduction
Digestion Nervous System
Circulation Hormones
Excretion

3. Unit 3 - Internal Features of Insects
Insect Muscles
Most muscles attach to the inside walls of the exoskeleton.
These muscles control movement:
Mouthparts, legs and wings
Air through the trachea
Food through the digestive system
Most muscle activity is controlled by the nervous system (just as with humans).
ENT063 - Spring 2006

4. Insect Respiratory System
Unit 3 - Internal Features of Insects
Insects breathe through small openings called spiracles that are found along the thorax and abdomen
Insects and some more advanced spiders have spiracles on their exoskeletons to allow air to enter the trachea.[2] In the respiratory system of insects, the tracheal tubes primarily deliver oxygen directly into the animals' tissues. The spiracles can be opened and closed in an efficient manner to reduce water loss. This is done by contracting closer muscles surrounding the spiracle. In order to open, the muscle relaxes. The closer muscle is controlled by the central nervous system but can also react to localized chemical stimuli. Several aquatic insects have similar or alternative closing methods to prevent water from entering the trachea. Spiracles may also be surrounded by hairs to minimize bulk air movement around the opening, and thus minimize water loss.[edit]
ENT063 - Spring 2006

5. Unit 3 - Internal Features of Insects
The respiratory system is important to the pest management professional. For example, some dusts that are otherwise nontoxic can clog the spiracles and thus deprive the insect of the oxygen it needs to live. Many insecticides, such as fumigants, actually diffuse into the insect body through the spiracles, permitting internal penetration through the tracheae and tracheoles.
University of Nebraska-Lincoln
Air travels throughout the body through tubes called tracheae
Unit 3
ENT063 - Spring 2006

6. Drain fly larvae

7. Insect Respiratory System
Some aquatic insects breathe through gills
discoverlife.org

8. Insect Respiratory System
Mosquitoes larvae breathe through siphons
photobucket.com

9. Respiratory Video

10. Unit 3 - Internal Features of Insects
Digestive System
The digestive system is a tube that is divided basically into three sections:
Foregut
Midgut
Hindgut
An insect’s digestive system is basically a tube that runs the full length of its body, which consists of various parts, as well as glands that enable the insect to digest food. These various parts are modified according to the type of food the insects eats. Insects have essentially the same nutritional requirements we do. They too, require fats, carbohydrates, proteins, vitamins and minerals.
ENT063 - Spring 2006

11. Digestive System
Foregut – mostly used for temporary storage, mixing and grinding.

12. Digestive System
Midgut - where most digestion and absorption of food occurs

13. Digestive System
Hindgut - where wastes are removed.

14. Insect Digestive System
University of Nebraska-Lincoln

15. Insect Digestion of Food
Unit 3 - Internal Features of Insects
Insect Digestion of Food
Most insects digest carbohydrates, proteins and fats.
Some insects, such as termites, have microorganisms called “symbionts” in their gut that digest cellulose or other materials for them to use as nutrients.
The required diet is frequently different in the immature stage and the adult stage of the same species. For example, mosquitoes feed on blood as adults and obtain other nutrients in the larval stage.
ENT063 - Spring 2006

16. Insect Circulatory System
Insects have an “open” circulatory system.
Their blood is about 90% liquid (plasma)
Blood travels through some blood vessels, then dumps into an open cavity.
Insects have a dorsal blood vessel that serves as their “heart”.
Accessory pulsating organs help push the blood through the legs, wings and antennae

17. Dorsal Blood Vessel
“Heart”
Aorta

18. Circulatory Video

19. The Insect Circulatory System
Unit 3 - Internal Features of Insects
The Insect Circulatory System
With most insects, blood is not used to transport oxygen
Bloodworms - Hemoglobin binds and holds a reserve supply of oxygen for times when oxygen in water is low.
Flyguys.net
ENT063 - Spring 2006

20. The Insect Circulatory System
Unit 3 - Internal Features of Insects
The Insect Circulatory System
Transports nutrients and waste products
Transports chemicals that are important for insect growth and development (hormones).
Certain cells in the blood heal wounds and also dispose of bacteria and other organisms
Maintains or changes the pressure inside the body
Localized pressure is used to expand the size of the body after molting and to expand the wings. The circulatory system plays an important role in the transport of insecticides to the sites of action within the body – insecticides entering the body by ingestion or through the cuticle are distributed throughout the insect’s body by the circulatory system.
ENT063 - Spring 2006

21. Insect Excretory System
Unit 3 - Internal Features of Insects
Insect Excretory System
Malpighian tubules – insect “kidneys” located at the junction of the midgut and hindgut
Purpose - similar to our kidneys
Remove wastes from the blood and digestive systems.
Filter out water for recycling through the body.
Insecticides that are ingested and broken down by the digestive enzymes usually leave the body through the excretory system. In some instances, such as with cat fleas feeding on an animal treated with systemic insecticide, the materials can pass through the digestive tract faster than they can be absorbed. Thus, the insecticide is relatively ineffective. However, if the flea’s feces is tainted with the insecticide, then the larvae (which feed on adult flea feces) could receive a lethal dose. Some slow-acting toxicants used in cockroach baits are excreted by the affected roaches before they die. Because roaches sometimes feed on one another feces, toxicants can be transferred to roaches that have not fed on the bait, thereby increasing the overall effectiveness of a baiting program.
ENT063 - Spring 2006

22. Insect Excretory System
Unit 3 - Internal Features of Insects
Insect Excretory System
The gastric caeca serve to increase the surface area of the midgut, thus increases both its ability to secrete digestive enzymes and its ability to extract useful products from the partially digested food.
ENT063 - Spring 2006

23. Reproductive System
Most insect species have two genders (sexes) - male and female
Some insects can control the gender of their offspring. For example - bees
unfertilized eggs produce males (drones)
fertilized eggs produce females
they may produce males at certain times of the year only

24. Reproductive System Parthenogenesis - reproduction without mating
All offspring from one female are genetically identical to her. (Example – aphids and whiteflies)
Can increases the likelihood of pesticide resistance developing.

25. Unit 3 - Internal Features of Insects
Nervous System
Insects have a ventral nerve cord (the opposite of mammals and other vertebrates)
They have a collection of nerve cells that compose a “brain”
They have a pair of nerve centers in each body segment, called ganglia
ENT063 - Spring 2006

26. Nervous System Role of the nervous system:
Collect and transmit sensory information such as:
Temperature, light, chemicals, etc.
Control responses (movement, molting, eating, etc.)

27. How the Nervous System Works
Unit 3 - Internal Features of Insects
How the Nervous System Works
Nerves control the muscles
A nerve impulse moves along the nerve cell (neuron).
The impulse then travels across a gap (synapse) between the neuron and the muscle that it controls
Unit 3
University of Nebraska-Lincoln
ENT063 - Spring 2006

28. How the Nervous System Works
Acetylcholine acts as “chemical bridge” across the gap.
Acetylcholinesterase - resets the synapse

29. How the Nervous System Works
Unit 3 - Internal Features of Insects
How the Nervous System Works
Organophosphate pesticides (e.g, Dursban and diazinon, Orthene) inhibit or interfere with acetylcholinesterase and prevent the nerves from resetting.
Result:
nerve keeps sending signals (doesn’t reset)
muscles keep twitching
insect dies
Same affect on human nervous systems
Pyrethroids and pyrethrins block impulse transmission along the nerve fibers. Avermectins block transmission of nerve impulses to muscles.
ENT063 - Spring 2006

30. Hormone Production
HORMONE - a chemical formed in an organ or body tissue that travels through the body and causes some effect on another body part.
Some hormones control
Molting
Growth and maturation to adulthood

31. Hormone Production
Some insecticides mimic these hormones - prevent the insect from molting or maturing or cause it to become an adult too quickly.

32. INSECT GROWTH & METAMORPHOSIS
ADULT
NYMPH
EGG

33. Questions?