Introduction to Insects

Introduction to InsectsBIO 402: Field Biology

Bumblebee on thistleSumter National ForestMay 2005

Insects are JumpStart September 7, 2010

PHYLUM ARTHROPODAArthropods are characterized by:Exoskeleton of chitin (must molt to grow)Jointed legsSegmented bodyVariable number of antennae for sensesBreath through a number of branching tubules

marine crab at Riverbanks Zoo

PHYLUM ARTHROPODATwo major subphyla are:

Subphylum Chelicerata (chelicerates)no antennaemouth parts with cheliceraeat least five pair of legs or leg-like appendagestwo distinct body segments

Include: horseshoe crab, sea spiders, arachnids

Sea spider (above)Brown recluse spider(right)Horseshoe crab (below)

PHYLUM ARTHROPODASubphylum Mandibulata (mandibulates)Have antennaeMouthy parts with mandiblesWidely variable number appendagesVariable number of body segments

Include: crustaceans, millipedes, centipedes and insectsMosquito (ul)Millipede (ur)Centipede (ll)Crayfish (lr)

INSECTSTrivia about insects:Over 1 million species worldwide90% are in the tropicsAbout 13,000 species in North CarolinaAbout 10,000 species in South Carolina

Stag Beetle

INSECT CHARACTERISTICSThree body segments (head, thorax, abdomen)One pair antennaeMouth parts containing a labrum, pair of mandibles, pair of maxillae, a hypopharynx and a labiumThree pair of legsOften 1-2 pair of wings (attached to thorax)A gonopore at posterior end of abdomenNo locomotor segments on the abdomen

INSECT DEVELOPMENTInsects grow by molting, commonly resulting in changeProcess leads to metamorphosis

METAMORPHOSIS TYPESSeveral types of metamorphosisSimple gets large with each moltGradual slow development of wings and other structuresIncomplete last molt dramatic:aquatic to terrestrial lifeComplete larvae pupae adultlarval forms commonly hard to identifyInsect Body StructureWe will look at the following components:HeadBody platesThoraxWingsLegsAbdomen

Head structuresCompound eyes typically presentpositioned above or behind the antennaevariation present in:size, shape, color

Ocelli also present are small, simple eyes located between or above the antennae & compound eyes1-3 in number

Head structuresA number of different types of antennae are presentsome are long and of one segment (butterflies)some have may segments (beetles)may also be clubbed (increase in diameter toward apex)

Head structuresMouth parts importantLABRUM - "upper lip"; broad & flap-likeMANDIBLES - heavily sclerotized, commonly tooth-like and nonsegmented- mostly for chewing- modified in some, long & skinny (true bugs)MAXILLAE - pseudotooth-like, segmented- include extentions, palps- modified by some to be long & tubular = styletsLABIUM - "lower lips"; broad, flap-likeHYPOPHARYNX - tongue-like structure

Head structuresIn most cases all the head plates are fused into one structure- can see divisions as sutures

Essentially all insects have one pair antennae- variation important in taxonomy: a) number segmentsb) overall length relative to heard sizec) presence of a capitate apex

Antennae

Body PlatesThree distinct positions:tergum upper, dorsalpleuron lateralsternum lower, ventral

ThoraxThree segments, a pair of legs on each- prothorax: 1st pair legs (no wings)- mesothorax: 2nd pair legs + 1st pair wings- metathorax: 3rd pair legs + 2nd pair wingsUpper or dorsal surface = pronotum, mesonotum, metanotumcommonly a large segment of metanotum between wings differs= scutellum, commonly will be triangularOpenings to tracheal system common on lateral meso- & metathorax (called spiracles)

WingsHave either one or two pair- Are outgrowths of the body cavity- Many wings are membranous and have a venation patternWing movement produced by change in thorax shapeVery important in identification of insects

WingsNumber of veins present (anterior to posterior)Costa (C) - along leading edge of wingsSubcosta (Sc)Radius (R) - commonly branched, R1, R2, etc.Median (M) - almost always branched onceanterior (MA), posterior (MP)Cubital plical (CuP) - Plical (Pl) and Vannals (V) - some groups these as the Anals (A)

WingsVeins connecting between the main veins are the cross veinsThese have names in some groups, as lower case letters- humeral (h)- radial (r)- sectorial (s)- radio-medial (r-m)- bmedial (m)- medio-cubital (m-cu)

The number of cross veins varies greatly- dragonflies (Odonata) with many

Wings

LegsAll have the following (from base to apex)Coxa (coxae) - typically smallTrochanter - typically smallFemur (femora) - typically the longerTibia (tibiae) - typically the longertip commonly has a spur(tympanum of crickets & some grasshoppers)Tarsus (tarsi) - commonly with 3-5 tarsomeres (lobes or parts)- the last typically has the claw(s)- also with a pad = pulvillus

LegsMuch variation present in size & shape of segmentsCommonly may see:- spines: rigid bristles- setae: flexible hairs

AbdomenOf eleven segmentstypically only 7-8 visible1st obscured by thoraxlast modified for reproductive functionsMany have tympanum on the first abdomenal segment (hearing)Spiracles commonly quite visible on the pleuronSome Orders with posterior cerci (pair - ex. Orthoptera) or caudal filament (one)some with all three (the silverfish, Thysanura)Reproductive structures may be quit evidentfemales with ovipositor and/or clapser

Morphological VariationA number of variations in morphology may make identification hardUpon death changes occur- drying causes them to shrink- alcohol causes them to expandGeneral color variation from one location to anotherMorphological VariationImmature forms of primitive orders will have shorter wings, etc.Newly emerged adults may have disproportionate 1) size ratios2) colorsDifference may also be due to sexual dimorphism