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

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

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). http://www.cals.ncsu.edu/course/ent425/library/tutorials/external_anatomy/locomotion.html ENT063 - Spring 2006

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

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

Drain fly larvae

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

Insect Respiratory System Mosquitoes larvae breathe through siphons photobucket.com

Respiratory Video

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

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

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

Digestive System Hindgut - where wastes are removed.

Insect Digestive System University of Nebraska-Lincoln

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

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

Dorsal Blood Vessel “Heart” Aorta

Circulatory Video

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

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

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

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

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

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.

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

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

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

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

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

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

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

INSECT GROWTH & METAMORPHOSIS ADULT NYMPH EGG

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