Arthropods

Insects and their relatives

Insects and Their Relatives

Characteristics– Exoskeleton (external covering)– Molts or sheds exoskeleton to grow– Undergo metamorphosis or pass through a

number of distinct growth stages during their lives

Metamorphosis

Simple or gradual– three changes

• egg• nymph

– 3-5 instars• adult

– adults and nymphs • eat same food

Metamorphosis

Complex or complete– four changes

• egg• larva• pupa• adult

– larvae and adults• eat different food

– larvae are destructive

External structure

Insects– 3 body regions

• head• thorax• abdomen

– 3 pair legs attached to thorax– 1 pair antennae– wings usually present in adult state.

External structure

Arachnids (spiders and mites)– 2 body regions

• cephalothorax• abdomen

– usually 4 pair legs – no wings– no antennae

Other Arthropods

Crustaceans– Pillbugs– Sowbugs

Mollusca– snails– slugs

Gray garden slug photo Ohio State University

Pillbugs - photo J. Kalish -UNL

Other Arthropods

Diplopoda– Millipedes

Chilopoda– Centipedes

Photo J. Kalish - UNL

Insect Orders

Beetles - Coleoptera

Largest order of insects (25,000 species in North America)Many species are plant feeders, some are predaceous (lady beetles)The term weevil refers to a snoutedbeetle

Beetles

Metamorphosis– Complete or complex

Mouth parts– Chewing (both adult and larvae)

Beetles - Adults

• Wing: 2 pair, the front pair (elytra) are greatly thickened and shell-like and when at rest meet in a straight line down the back. Hind membranous wing pair is protected by front pair.

Beetles - Larvae

Larvae that feed externally on plants are typical “grub” with head capsule, 3 pair of legs on the thorax, and no legs on the abdomen

Beetles - Larvae

Larva that feed internally in plants (e.g. bark beetles, weevils, woodborers) typically lack legs. Chewing mouthparts

Earwigs- Dermaptera

Introduced from EuropeMetamorphosis: gradual or simpleMouthparts: chewing, general feeders on decaying organic matter, occasionally feed on plants and insects. Can pinch with mouthparts.

Earwigs

Wings: 2 pair; front wings are short leathery without venation and meet in a straight line down the back when at rest. Can be confused with those of beetles, but beetles do not have forceps-like cerci.

Earwigs

Body: Elongated, flattenedCerci: Tail-like pinchers. The cerci on males are bowed, while straight on females. Cerci cannot produce a painful pinch.Habit: Over winters as adults. During the day, earwigs like to hide in dark, moist areas.

Flies, Gnats, Midges, Mosquitoes- Diptera

Second only to beetles in number.Feeding habits vary widely– Scavengers (house flies, blow flies)– Blood feeding (mosquitoes)– Plant galls (gall midges)– Predators (flower flies, robber flies)– Aquatic

Flies, Gnats, Midges, Mosquitoes

If the fly is a Diptera, the name is written as two words (house fly, deer fly). If the fly is not a Diptera, the name is written as one word (sawfly, butterfly, whitefly)

Flies, Gnats, Midges

Metamorphosis : Complete

Flies, Gnats, Midges -Adult

Wings: 1 pair of wings (an easy ID forDiptera). Adults are typically soft bodied and often hairy.– Note: They may look like bees, wasps or

flies---count the wings! On many Hymenoptera the wings may be attached and the hind wings may be hidden under the front wing.

Flies, Gnats, Midges- Adult

Mouthparts: highly variable– Sponging (house fly)– Cutting-lapping (horse fly)– Piercing-sucking (mosquito)

Flies, Gnats, Midges - larvae

Vary greatly in appearance. Larva of advanced forms, like the house fly, are maggot type having mouth hooks and not head capsule or legs.

Lower forms, such as mosquitoes, have a small head capsule.

HemipteraTrue bugs: plant bugs, squash bugs, stink bugs

Order includes many important predators.If the bug is a Hemiptera the name is written as two words (stink bug, water bug, squash bug). If the insect is not aHemiptera, the name is written as one word (ladybug)

True Bugs

Metamorphosis: gradual or simpleMouthparts: piercing-sucking. Mouthparts usually easily visible and appears to arise from front of head, ahead of eyes. By contrast Homopteramouthparts are not very visible and appear to arise from the area between the front pair of legs.

True Bugs

Wings: 2 pair. Front wings (calledhemielytra) are thickened at base and membranous at end, and overlap at tips when at rest. Hind wings are membranous. Nymphs have no wings, but wing pads may be visible in older nymphs.

True Bugs

Body: Usually broad and somewhat flattened; a triangular plate (thescutellum) is located between the base of the wings.

HomopteraAphids, cicadas, leafhoppers, mealybugspsyllids, scales, whitefiles

All species are plant feeders, often feeding on phloem sap.Excretion of honey dew is common to many members of the order.

Insects in this order are carriers (vectors) of several plant pathogens.

honeydew

Aphids and Psyllids, etc

Metamorphosis: gradual; nymphs and adults similar in appearance (except scales and whiteflies)

Aphids and Psyllids, etc

Mouthparts: Piercing-sucking; jointed beak-like mouthparts. Not very visible and appear to arise from the area between the front pair of legs. By contrast,Hemiptera mouthparts are usually easily visible and appear to arise from the front of the head, ahead of the eyes.

Aphids and Psyllids, etc

Wings: 2 pair of membranous wings; generally held roof-like over the body when at rest. Many wingless forms occur. No wings on nymphs, but wing pads may be observed on older nymphs.

HymenopteraAnts, bees, horntails, sawflies, wasps

Order includes many important parasites and predators.The order has the most highly developed insect behaviors and social patterns.

Bees, Wasps, Sawflies

Metamorphosis: completeMouthparts: chewing or chewing-sucking

Bees, Wasps, Sawflies - Adult

Wings: 2 pair membranous wings, often hooked together. Hind pair are usually smaller.Mouthparts: typically chewing or chewing-sucking

Bees, Wasps, Sawflies - Adult

Body: Adults are rather soft-bodied or slightly hardened bodies. Most species have a distinct constriction between the thorax and abdomen (wasp waist). Exception: sawfly/horntail group does not have the wasp waist.

Antennae: jointed sometimes elbowed.Stinger: female abdomen usually provided with a saw, piercing organ, or stinger.

Bees, Wasps, Sawflies - Larvae

Larva of most species are rarely observed, often developing in a nest or as an internal parasite.Head: a distinct head capsuleMouthparts: chewing

Bees, Wasps, Sawflies - Larvae

Legs: none (except some sawfly larva)– Note: Sawfly larva may look like

caterpillars. Caterpillars have up to 5 pair of prolegs on abdomen. Sawfly larvae have 6+ pair prolegs on abdomen.

LepidopteraButterflies, moths, skippers

Metamorphosis: completeMouthparts: coiled sucking tube (lapping) as adults. Some adults don’t feed at all. As larvae have chewing mouthparts

Butterfly Cocoon Caterpillar Egg Mass

Butterflies, Moths, Skippers -Adult

Wings: 2 pair often large, covered with small overlapping scales, often but not always brightly colored.

Black Swallowtail

Black swallowtail larva

Butterflies and Moths- Adults

Butterflies have slender bodies, the wings are held vertical when at rest, and the antennae are slender and club like at the tips. They are day fliers.Moths have stout bodies and wings are held

in a roof like horizontal position over the body when at rest. Antennae are variable in form, but usually filamentous of featherlike. Most fly at night

Skippers - Adults

Skippers dart or skip through the air in flight during the day. Their bodies are intermediate in form, between the moths and common butterflies. Their wings are held erect when at rest. The antennae of skippers are club-like at the tips, and often have hook-like ends of the club or knob.

Lepidoptera larvae:Caterpillars

Legs: 3 pair of legs on thoraxProlegs: Up to 5 pair of prolegs (fleshy leg-like structure with hook-like crochets on the end) on some abdominal segments.)– Note: Sawfly larvae look like smooth

bodied caterpillars but have more than 5 pair of prolegs on the abdomen. Their bodies also taper from the head.

Caterpillars

Decorations: Often highly colored or decorated with spines or other appendages.Mouthparts: Chewing mouthparts with voracious appetites.

Variegated Fritillary LarvaVariegated Fritillary Adult

ThysanopteraThrips

Very common insects, but due to the tiny size are rarely observed.Feeding leaves the plant looking scarred, as they rasp the leaf or flower surface and suck plant fluids.

Thrips

Thrips

Metamorphosis: a variation of gradualMouthparts: rasping-suckingWings: 4 (2 pair) slender wings fringed with hairs, often absent.Tarsi: Feet are 1 or 2 segmented, each with a balloon-like structure on the end.Size: minute, less than 1/8 inch long.

OrthopteraCrickets, grasshoppers, katydids

Most are plant feeders. A few are predators.Note: Some books place Mantodea(mantids), Phasmida (walking sticks) and Blattaria (roaches) in the orderOrthoptera.

Grasshoppers and Crickets

Metamorphosis GradualMouthparts: chewingWings: Usually have 2 pair of wings. Front wings more or less parchment-like with distinct venations. Wings may overlap at rest. Wings may be used to make sounds.

Grasshoppers and Crickets

Legs: Hind legs designed for jumping.Antennae: thread-like.Cerci: 1 pair tail-like appendages on most adults.

Insect relatives - Mites

Two body segments 8 legs.Tiny soft- bodied organisms that appear almost everywhere.Adult and immatures have sucking mouthpartsTwo types– spider mites– eriophyid mites

Spider mites

Mites

Foliage, buds, stems, and fruit of infested plants may become red, bronze, yellow, white or brown. Spider mites spin webs.

Stippling or mottling symptom of spider mite feeding.