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Insects External Anatomy Adult insects are known for having three major body regions, six legs, one pair of antennae and usually two pair of wings as adults. head thorax abdomen Adult insects develop as a composite of fused segments with specific body part associations. from the 1995 Physiology or Medicine Nobel Poster HEAD antennae compound eyes The first body region is the head. Insect heads can be highly variable, but most possess eyes, antennae and mouthparts. head mouthparts Antennae beetle butterfly ant fly termite June beetle Antennae are used by insects as major sensory devices, especially for smell, and can be adaptive for the insect in many ways. Two Examples of Mouthparts chewing piercing/sucking Insect mouthparts are also highly modified for the insect. Chewing, biting, or sucking, are a few examples. Mouthparts of an immature insect may differ from those of the same insect in its adult stage. Arthropod Vision • Simple eyes – Light sensitive cells share a common lens • Compound eyes – Thousand of closely packed units called ommatidia Simple ocelli. Complex lensed ocelli. Compound eyes made of ommatidia. Compound & Simple Eyes Picture of bodyparts The middle body region is called the thorax and is composed of three fused segments. All legs and wings are located on the thorax. Thorax swimming digging suction Legs grasping Like the mouthparts and antennae, insect legs are quite variable in form and function and reflect the insect's lifestyle. Walking Walking involves the coordinated movement of uniramous appendages in different planes. Walking Subphylum Myriapoda Millipedes (Class Diplopoda) have two legs per segment on each side. Slow but powerful. Centipedes (Class Chilopoda) have one leg per segment on each side. Fast but not as powerful. Flying Hemipterans (flies) Indirect flight muscles allow wings to beat faster than neural transmission. Dorsoventral and longitudinal muscles. Flexible thorax. The last body region is called the abdomen. It is composed of many segments connected by flexible sections allowing it great movement. Abdomen Insects possess an exterior covering called the exoskeleton. They do not have internal bones. This segmented "shell" is what gives insects shape and can be very hard in some insects. It is often covered with a waxy layer and may have "hairs" called setae. seta ( hair) waxy layer Exoskeleton x-sec Internal Anatomy Inside the insect we find the systems for respiration, circulation, nerves, and digestion, but there is little resemblance to the same systems found in man or other mammals. Digestive System foregut hindgut Digestive sys midgut The digestive system is a tube that opens at the mouth and empties at the tail end of the insect. It is divided into three parts called the foregut, midgut, and hind gut. In some insects such as the honey bee, the foregut acts as a crop to carry or hold liquids which can be regurgitated later. Circulatory System “ heart ” aortic pumps Circ system The circulatory system is not composed of a central heart, veins and arteries which circulate blood cells and transport oxygen. The insect circulatory system is a simple tube down the back which is open at both ends and slowly pulses body fluids and nutrients from the rear of the insect to the head. Insects have a less centralized nervous system than humans. The nerve chord runs along the ventral or bottom aspect of an insect. The brain is divided into two main parts. The largest lobes control important areas such as the eyes, antennae, and mouthparts. Other major concentrations of nerve bundles called ganglia occur along the nerve chord and usually control those body functions closest to it. two lobed brain Nervous system nerve bundles (ganglia) Nervous System The respiratory system is composed of air sacs and tubes called tracheae. Air enters the tubes through a series of openings called spiracles found along the sides of the body. The largest spiracles are usually found on the thorax where greater musculature from wings and legs require more oxygen. There are no spiracles on the head. spiracles Respiratory System tracheal tubes “Brain” is 2-3 ganglia with specific functions. Ganglionated ventral nerve cord. Sense organs (sensilla) protrude out of cuticle. Can be slit in cuticle. Membranous drums. Chemoreceptors with thin cuticle. How do Arthropods reproduce and develop? Most gonochoristic with formal mating and internal fertilization. Life Cycles The many diverse orders of insects have four different types of life cycles. These life cycles are called "metamorphosis" because of the changes of shape that the insects undergo during development. egg Without Metamorphosis nymphs adult Without meta The first type is "without" metamorphosis which the wingless primitive orders such as silverfish (Thysanura) and springtails (Collembola) possess. The young resemble adults except for size. Incomplete Metamorphosis egg naiads adult Incomplete meta The second type is "incomplete" metamorphosis which is found among the aquatic insect orders such as mayflies (Ephemeroptera) and dragonflies (Odonata). Gradual Metamorphosis The third type is "gradual" metamorphosis seen in such orders as the grasshoppers (Orthoptera), termites (Isoptera), thrips (Thysanoptera) and true bugs (Hemiptera). This life cycle starts as an egg, but each growth, or nymphal stage looks similar, except it lacks wings and the reproductive capacity that the adult possesses. egg nymphs adult Complete Metamorphosis The fourth type is "complete" metamorphosis found in butterflies (Lepidoptera), beetles (Coleoptera), flies (Diptera), and bees, wasps, and ants (Hymenoptera). This life cycle has the four stages of egg, larva, pupa, and adult. Each stage is quite distinct. egg larvae pupa adult It should be noted that because insects are hard-bodied, they cannot grow larger gradually. Instead they grow larger in steps by shedding the hard exoskeleton for a brief period of expansion. The brief periods between or within stages are called molts. Insects are soft-bodied and vulnerable during this time. recently molted roach Molting • Secretion of "molting fluid" to dissolve old endocuticle. • New cuticle formed under old exocuticle. • Break out of old cuticle – Old cuticle breaks at line of weakness Growth stages • Arthropod passes thru 3-20+ growth stages in life cycle. • Some stop molting as adults (insects, most spiders) • Some continue to molt (crayfish, tarantulas) Soldier Beetles Order Coleoptera Family Cantharidae David Laughlin Life History: Adults on flowering shrubs and trees. Larvae in soil. Prey: Aphids, locust eggs, snails, slugs, millipedes, earthworms, caterpillars, and maggots. Ground Beetles Order Coleoptera Family Carabidae Life History: Nocturnal, in or on soil, some live up to four years. Prey: Caterpillars, soil and tree insects, earthworms. Top: Harpalus sp. Bottom: Calosoma sp. Vera Krischik Tiger Beetles Order Coleoptera Family Cicindellidae Life History: Stalking predators, fast runners. Prey: Whatever they can catch. John Davidson Rove Beetles Order Coleoptera Family Staphylinidae Life History: Nocturnal predators. Prey: Soil-dwelling insects. Lady Beetles Order Coleoptera Family Coccinellidae Life History: Many species, both larvae and adults are predaceous. Jeff Hahn Prey: Aphids, scale insects, mealybugs, whiteflies, spider mites, insect eggs. Pink Lady Beetle (Coleomegilla maculata), a native lady beetle Convergent Lady Beetle Order Coleoptera Family Coccinellidae Hippodamia convergens Life History: Native and common in the Midwest; larvae and adults are both predaceous. Prey: Aphids. John Davidson Multicolored Asian Lady Beetle Order Coleoptera Family Coccinellidae Harmonia axyridis John Davidson Life History: Introduced, invades homes in fall. Prey: Aphids and scales. John Davidson John Davidson Robber Flies Order Diptera Family Asilidae Whitney Cranshaw Life History: Larvae live in soil and decaying wood; adults are fast fliers. Prey: Butterflies, wasps, bees, dragonflies, grasshoppers, beetles, and other flies. Larvae feed on soft-bodied insects such as grasshopper eggs, white grubs, and other insect larvae. Gall Midges Order Diptera Family Cecidomyiidae Life History: Tiny adults feed on honeydew and nectar, larvae are predaceous. Prey: Larvae feed on aphids, mites, scales, whiteflies, and thrips. Whitney Cranshaw Top and bottom: Aphidoletes aphidimyza feeding on aphids Syrphid or Hover Flies Order Diptera Family Syrphidae Life History: Adults feed on nectar and pollen. Larvae are predaceous. One generation every 2 to 4 weeks. David Laughlin Prey: Larvae feed on aphids, scales, and other insects. Tachinid Flies Order Diptera Family Tachinidae John Davidson Life History: Adults lay eggs on plants or hosts. Larvae develop inside hosts and pupate in 4 to 14 days. One or more generations per year. Prey: Caterpillars, adult and larval beetles, sawfly larvae, true bugs, grasshoppers, and others. Minute Pirate Bugs Order Hemiptera Family Anthocoridae Life History: One generation takes 20 days to complete, multiple generations per year. Orius insidiosus adult Prey: Spider mites, insect eggs, aphids, thrips, scales, caterpillars. Seed and Big-Eyed Bugs Order Hemiptera Family Lygaeidae Life History: Many Lygaeids feed on plants, but some are predaceous. Prey: Insect eggs, aphids, mealybugs, spider mites, leafhoppers, plant bugs, whiteflies, caterpillars, and beetle larvae. Top and bottom: Geocoris species John Davidson Pirate Bugs Order Hemiptera Family Miridae John Davidson Life History: Most mirids feed on plants, but some are predaceous. Prey: Mites and plantfeeding insects; lace bugs, cotton aphid, tobacco budworm. David Laughlin Top: Deraeocoris nebulosus adult Bottom: Pirate bug adult (L) and nymph (R) Stink Bugs Order Hemiptera Family Pentatomidae Life History: Most feed on plants, but some are predaceous. Many discharge a distasteful smell when handled. Whitney Cranshaw Predatory stink bug feeding on elm leaf beetle larva Prey: Caterpillars and beetles such as Colorado potato beetle and Mexican bean beetle. Stink Bugs David Laughlin CW from top left: Podisus maculiventris adult attacking tussock moth caterpillar, Perillus bioculatus nymph feeding on beetle larva, P. bioculatus nymph feeding on hornworm Whitney Cranshaw John Davidson Assassin Bugs Order Hemiptera Family Reduviidae Life History: Assassin bugs feed by piercing prey with their beaks to suck out juices. Prey: Caterpillars, small flying insects, aphids, and leafhoppers. Wheel bug (Arilus cristatus) Aphelinid Wasps Order Hymenoptera Family Aphelinidae Life History: Solitary, lay eggs in or outside hosts. Females usually reproduce parthenogenetically, males are rare. John Davidson Encarsia formosa adult Prey: Aphids, mealybugs, psyllids, scales, and whiteflies. Braconid Wasps Order Hymenoptera Family Braconidae Life History: Life cycle is 10–14 days. Larvae are internal parasitoids; many pupate outside hosts. More females than males. John Davidson Prey: Aphids, larvae of beetles, flies, sawflies, and caterpillars; tomato hornworm, imported cabbageworm, gypsy moth. Chalcid Wasps Order Hymenoptera Family Chalcidae Life History: Larvae are internal parasitoids of other insects. John Davidson Prey: Moths, butterflies, beetles, flies, other wasps. David Laughlin Encyrtid Wasps Order Hymenoptera Family Encyrtidae John Davidson Life History: Larvae are parasitoids; adults live 2–3 days. Prey: Ticks, insect eggs, larvae, and pupae; beetles, bugs, moths, mealybugs, scales. John Davidson Top: Encyrtus fuscus reared from hemispherical scale Bottom: Parasitized hemispherical scales turned black Ichneumonid Wasps Order Hymenoptera Family Ichneumonidae Life History: Larvae are internal or external parasitoids. Whitney Cranshaw Prey species: Larvae and pupae of beetles, wasps, and caterpillars; armyworms, cabbage looper, fall webworm, oakworms, tent caterpillars, tussock moths, European corn borer. Scelionid Wasps Order Hymenoptera Family Scelionidae Life History: Larvae are internal parasitoids of other insects and spiders. Prey: Insect and spider eggs, especially those of true bugs and moths. John Davidson Trichogramma Wasps Order Hymenoptera Family Trichogrammatidae University of California at Berkeley Life History: Larvae are internal parasitoids of other insects. Prey: Sawfly and moth eggs; cabbageworm, tomato hornworm, corn earworm, codling moth, cutworm, armyworm, cabbage looper, European corn borer, tomato fruitworm. Vespid Wasps Order Hymenoptera Family Vespidae Life History: Many have annual colonies with queens, workers, and males. John Davidson Yellowjacket with caterpillar Prey: Caterpillars and other insects. May bother people at picnics. Paper wasp (Polistes species) Ants Order Hymenoptera Family Formicidae Life History: Annual colonies with queens, workers, and drones (males). Prey: Other arthropods, as well as pollen, nectar, and human food. Workers with eggs Jim Occi, BugPics, www.insectimages.org Ants Clemson University, USDA Cooperative Extension Slide Series, www.forestryimages.org Above: Carpenter ant (Camponotus sp.) Right: Red imported fire ants (Solenopsis invicta) with cerambycid larvae Herbert A. "Joe" Pase III, Texas Forest Service, www.insectimages.org Green Lacewings Order Neuroptera Family Chrysopidae Life History: Oval, white eggs laid singly on stalks 8 mm long. Small gray larvae spin cocoons and pupate on undersides of leaves when they are 10 mm long. One to ten generations per year. Prey: Larvae feed on aphids and other small insects. Adults feed on honeydew and pollen. Brown Lacewings Order Neuroptera Family Hemerobiidae John Davidson Life History: Oval, white eggs laid singly. Small gray larvae spin cocoons and pupate on undersides of leaves when they are 10 mm long. One to ten generations per year. Prey: Mites, aphids, mealybugs, scales, whiteflies, and other soft-bodied arthropods. Mantidflies Order Neuroptera Family Mantispidae David Laughlin Life History: Nocturnal insects that resemble mantids. Both larvae and adults are predaceous. Prey: Spider egg sacs, bee and wasp larvae. Predatory Thrips Order Thysanoptera Families Aleolothripidae and Phlaeothripidae Life History: Sexual or asexual reproduction. Nymphs resemble adults in size and color. Several generations per year. John Davidson Prey: Pest thrips, aphids, mites, whiteflies, and other soft-bodied insects. Centipedes Class Chilopoda Life History: Nocturnal; in gardens and houses. Prey: Small arthropods. Tree of Life http://tolweb.org/tree/phylogeny.html Tree of Life http://tolweb.org/tree/phylogeny.html Left: Lithobius forficatu Above: House centipede (Scutigera coleoptrata)