Insects All Materials © Cmassengale
Phylum Arthropoda Subphylum Uniramia Class Insecta
Characteristics
- Largest arthropod group
- Found in freshwater & terrestrial habitats, especially tropical areas
- Legs, mouthparts, & antenna jointed
- Body segmented into three sections — head, thorax, & abdomen
- Six legs & up to two pairs of wings located on thorax
- Have compound & simple eyes
- One pair of antennae on head
- Abdomen has 11 segments
- Exoskeleton, covering & protecting body, is made of chitin & must be molted to grow
- Elaborate mouthparts include:
* Mandibles – jaws
* Maxillae – paired sensory structures that move food to mouth
* Labium – lower lip
* Labrum – upper lip
* Palpi – used for tasting - Known as mandibulates
- Spiracles on abdomen open into tracheal tubes for oxygen & carbon dioxide exchange
- Tympanic membranes on 1st abdominal segment aid in hearing
- Thorax divided into 3 sections — prothorax, mesothorax, & metathorax
- One pair of legs on each thoracic segment
- Wings located on mesothorax & metathorax
- Ovipositor located on the end of the abdomen in female insects & used to dig hole & lay eggs
Common Insect Orders
- Orthoptera – grasshoppers, crickets, & cockroaches 2 pairs of straight wings & chewing mouthparts)
- Isoptera – termites (feed on wood)
- Dermaptera – earwigs (pincers on end of abdomen)
- Anoplura – sucking lice (wingless parasites)
- Hemiptera – true bugs (have triangular-shaped scutellum & last 1/3 of wings membranous)
- Homoptera – aphids & cicadas (membranous wings held roof-like over body
- Ephemeroptera – mayflies (have 2 cerci on tail, membranous wings, & nonfunctional mouthparts in adults)
- Odonata – dragonflies & damselflies (2 pairs of equal size, membranous wings, strong fliers, feed on other insects)
- Neuroptera – Dobson flies & lacewings (2 pairs of membranous wings)
- Coleoptera – beetles (hard forewings or elytra, membranous hindwings)
- Lepidoptera – butterflies & moths (powdery scales covered wings
- Diptera – flies & mosquitoes (one pair of wings, 2nd pair modified into balancing structure called halteres)
- Siphonaptera – fleas (parasites on birds & mammals, wingless as adults)
- Hymenoptera – bees, ants, & wasps (stinger on abdomen for protection, may live together in groups, pollinators)
Click Here for Pictures of Insect Orders
Success of Insects
- Found everywhere except in deep part of ocean
- Very short life span & rapidly adapt to new environments
- Small size helps minimize competition in habitats
- Flight helps escape predators & move into other environments
Environmental Impact
- Pollinate almost 2/3’s of all plants
- Serve as food for fish, birds, & mammals
- Help recycle materials (termites recycle wood)
- Make useful byproducts such as silk & honey
- Some spread disease
- Agricultural pests
Grasshoppers
External Structure
- Head with antenna, compound eyes, & chewing mouthparts
- Walking legs on prothorax & mesothorax; jumping legs on metathorax
- Tarsus are lower leg segments with spines, hooks, & pads
- Leathery, protective forewings on mesothorax & membranous hindwings for flight on metathorax
- Covering over thorax called pronotum
Internal Structure
Digestive & Excretory Systems
- Cutting & chewing mouthparts (labium, labrum, mandibles, & maxillae)
- Saliva added to food in mouth
- Esophagus carries food to crop for temporary storage
- Gizzard has chitinous plates to grind food
- Midgut (insect’s stomach) has gastric caeca (pouches) to secrete digestive enzymes to break down food
- Food is absorbed into the body cavity or coelom in the hindgut (composed of the colon & rectum)
- Malpighian tubules filter chemical wastes from the blood & deposit them in the rectum where they leave through the anus
Circulatory System
- Open circulation of blood
- Aorta is the largest blood vessel carrying blood to the body cells
- Hearts are muscular regions of the aorta in the posterior end of the abdomen that pump blood toward head
- Blood flows back toward abdomen carrying digested food & re-enters the aorta through openings called ostia
Respiratory System
- Air enters through openings called spiracles along the sides of the abdomen & enters into tracheal tubes that branch into smaller tracheoles where gas exchange with body cells occurs
- Tracheal tubes carry oxygen to body cells & return carbon dioxide to leave the body though spiracles
Nervous System
- Simple brain, nerve cords, & ganglia
- Three simple eyes or ocelli (detect light) & a pair of compound eyes (can detect movement but not images)
- Tympanic membrane on 1st abdominal segment
- Pair of antenna contains sense organs for touch, taste, & smell detects sound
- Sensory hairs found on parts of the body
- Palpi for taste
Reproductive System
- Reproductive organs (ovaries & testes) located in abdomen
- Male deposits sperm into female’s seminal receptacle
- Stored sperm fertilizes eggs as they are released by female
- Ovipositor on tip of female’s abdomen is used to lay eggs
- Separate sexes
- Lay large number of eggs to ensure survival
Development
- Most insects go through changes in form & size called metamorphosis
- Some insects such as silverfish don’t go through metamorphosis
- Incomplete metamorphosis goes from egg to nymph (immature form that looks like adult but without fully developed wings) to adult (3 stages)
- Instars are growth periods between molts of nymphs & larva
- Grasshoppers, termites, & true bugs go through incomplete metamorphosis
HEMIPTERAN (TRUE BUG) NYMPH
- Complete metamorphosis goes from egg to larva (segmented & wormlike) to pupa to adult (4 stages)
BUTTERFLY LARVA (CATERPILLAR)
- Butterflies, beetles, & flies go through complete metamorphosis
- In pupal stage, larval tissues break down & cells called imaginal disk develops into tissues of the adult
- Cocoon or chrysalis is a protective case formed around the pupa
BUTTERFLY COCOON
- Metamorphosis controlled by hormones
* Brain hormone stimulates the release of molting hormone (ecdysone)
* When juvenile hormone level high, larva molts
* When juvenile hormone level low, larva pupates
* When juvenile hormone absent, adult emerges from pupal case - Different stages of metamorphosis eliminates competition between larva & adults for food & space
- Multi-stage life cycle helps insects withstand harsh weather
- Different stages have different functions (caterpillar/growth & adult/reproduction)
Defense Mechanisms
- Bombardier beetle sprays noxious chemical
BOMBARDIER BEETLE
- Wasps & bees can sting
- Some insects use camouflage to blend into their environments
- Some insects taste bad & have warning colorations
PAPER WASP
- Mullerian mimicry – poisonous or dangerous species have similar patterns of warning coloration so predators avoid all the species (black & yellow stripes on bees & wasps)
- Batesian mimicry – species that are nonpoisonous or not bad tasting have colorations that mimic other poisonous or bad tasting species (Viceroy butterfly mimics bad tasting Monarch)
Insect Communication
- Insects may communicate with each other using sound (cricket chirps), light (firefly), or “dances” (honeybee)
- Pheromones are chemicals released by some insects to attract mates or mark trails
Insect Behavior
- Insects may be solitary or social
- Social insects (bees, ants, & some wasps) live together in groups & share work (division of labor)
- Social insects have a caste system with different individuals doing different jobs
- Honeybee caste system:
* Workers
– sterile females
– care for queen & feed her honey and pollen
– make beeswax for hive
– fan wings to cool hive
– eat honey
– collect nectar, pollen, & royal jelly
– live about 6 weeks
– nurse bees care for larva
– secrete royal jelly to feed new queen
* Drones
– males
– mate with queen
– feed by workers
– driven out of hive to conserve food during winter
* Queen
– reproductive female
– mate only once but store sperm for up to 5 years in seminal receptacles
– feed by workers
– secretes chemical called queen factor that prevents other females from sexually maturing
– leaves hive with 1/2 the workers if there is overcrowding
HONEYBEE HIVE
Smithers thinks that a special juice will increase the productivity of workers. He creates two groups of 50 workers each and assigns each group the same task (in this case, they’re supposed to staple a set of papers). Group A is given the special juice to drink while they work. Group B is not given the special juice. After an hour, Smithers counts how many stacks of papers each group has made. Group A made 1,587 stacks, Group B made 2,113 stacks.
Homer notices that his shower is covered in a strange green slime. His friend Barney tells him that coconut juice will get rid of the green slime. Homer decides to check this out by spraying half of the shower with coconut juice. He sprays the other half of the shower with water. After 3 days of “treatment” there is no change in the appearance of the green slime on either side of the shower.
he’s been reading too much Radioactive Man). He decides to perform this experiment by placing 10 mice in a microwave for 10 seconds. He compared these 10 mice to another 10 mice that had not been exposed. His test consisted of a heavy block of wood that blocked the mouse food. he found that 8 out of 10 of the micro waved mice were able to push the block away. 7 out of 10 of the non-micro waved mice were able to do the same.
Krusty was told that a certain itching powder was the newest best thing on the market, it even claims to cause 50% longer lasting itches. Interested in this product, he buys the itching powder and compares it to his usual product. One test subject (A) is sprinkled with the original itching powder, and another test subject (B) was sprinkled with the Experimental itching powder. Subject A reported having itches for 30 minutes. Subject B reported to have itches for 45 minutes.
