Entomology By Dr. Fan dong

Insect Thorax The thorax consists of three segments - the prothorax (front), the mesothorax (middle) and the metathorax (back). Each of these segments bears a pair of jointed legs.

In winged insects, the meso- and metathoracic segments each bear a pair of wings--the forewings and hindwings forewings hindwings

In many insects one or both pairs of wings have been lost, or modified into other structures, during the course of evolution.

Construction of thorax Prothorax: Pronotum Propleuron: pleural sulcus-episternum and epimeron prosternum

Construction of Pterothorax Notum: three sulcus: antecostal sulcus, prescutal sulcus, scutoscutellar sulcus Acrotergite, prescutum, scutum, scutellum Anterior notal wing processes and posterior notal wing processes

scutellum

Construction of Pterothorax Pleuron : pleural sulcus-episternum and epimeron Sternum : two sulcus: presternal sulcus and sternacostal sulcus Eusternum (presternum , basisternum , sternellum) and intersternite

Thoracic legs coxa trochanter femur tibia tarsus pretarsus: claws pulvillus arolium

Mosquito’s femur (2070x)

Drosophila: claw and pulvillus

Types of thoracic legs Walking legs : ambulatorial legs Jumping legs : saltatorial legs Grasping legs : raptorial legs Digging legs : fossorial legs Swimming legs : natatorial legs Clasping legs Pollen-carrying legs : corbiculate legs Clinging legs : scansorial legs

Walking legs

Digging legs

Jumping legs

Grasping legs

Pollen-carrying legs

Clasping legs

Swimming legs

Clinging legs

Insect wings

Functional wings exist during the adult stage Membranous, parchment-like, or heavily sclerotized Most insects have two pairs of wings -- one pair on the mesothorax and one pair on the metathorax

Purpose of Flight in Insects Search for food or a resting habitat Escape from enemies and search actively for mates Be able to spread over the globe; if conditions became unfavorable in one place, they took to the air to find another                                                          

Function of wings serve as organs of flight protective covers (Coleoptera and Dermaptera) thermal collectors (Lepidoptera) gyroscopic stabilizers (Diptera) sound producers (Orthoptera) visual cues for species recognition and sexual contact (Lepidoptera).

In most cases, a characteristic network of veins runs throughout the wing tissue.   These veins are extensions of the body's circulatory system.   They are filled with hemolymph and contain a tracheal tube and a nerve.   In membranous wings, the veins provide strength and reinforcement during flight.   Wing shape, texture, and venation are quite distinctive among the insect taxa and therefore highly useful as aides for identification.

Structure of insect wing

Apical angle of a mosquito (80x)

Special wing modifications include the structures called halteres found in the Diptera (true flies), and the structures called elytra (singular: elytron) found in the Coleoptera (beetles) and Dermaptera (earwigs):

Membranous wings: such wings are very thin and like cellophane Types of insect wings Membranous wings: such wings are very thin and like cellophane

Elytra -- hard, sclerotized front wings that serve as protective covers for membranous hind wings Coleoptera

Hemelytra -- front wings that are leathery or parchment-like at the base and membranous near the tip Hemiptera

Tegmina -- front wings that are completely leathery or parchment-like in texture

lepidotic wings: Scaly wings -- front and hind wings covered with flattened setae (scales) Lepidoptera

Piliferous wings: Hairy wings -- front and hind wings clothed with setae Trichoptera

Fringed wings -- slender front and hind wings with long fringes of hair                                                 

Halteres -- small, club-like hind wings that serve as gyroscopic stabilizers during flight

Halteres

front wings and hind wings

Jugate form

Frenulum -- Bristle near base of hind wing that holds front and hind wings together Lepidoptera

amplexi form

Hamuli -- tiny hooks on hind wing that hold front and hind wings together Hymenoptera

fold form

Wing Venation Insect contained 7 longitudinal veins. These veins (and their branches) are named according to a system devised by John Comstock and George Needham -- the Comstock-Needham System

longitudinal veins Costa (C) -- the leading edge of the wing Subcosta (Sc) -- second longitudinal vein (behind the costa), typically unbranched Radius (R) -- third longitudinal vein, one to five branches reach the wing margin Media (M) -- fourth longitudinal vein, one to four branches reach the wing margin Cubitus (Cu) -- fifth longitudinal vein, one to three branches reach the wing margin Anal veins (A1, A2, A3) -- unbranched veins behind the cubitus Jugal veins ( J )

Crossveins crossveins abbreviation longitudinal veins ligated humeral crossvein radial crossvein sectorail crossvein radiomedial crossvein medial crossvein mediocubital crossvein h r s r-m m m-cu C/Sc R1/R2 R5/R4, or R2+3/R4+5 R4+5/M1+2 M2/M3 M3+4/Cu1

Variation of veins Increase：accessory veins –R1a, R1b intercalary veins—IM1 Decrease: combination

Cells Cell Enclosed cell Open cell Open cell Enclosed cell

Veins and cells

Articulation Articulation is an important condition for wing’s all sort of activities. At the end of wings there are some ossicles as joints-pteralia Humeral plate Axillary plates First axillary plates; second axillary plates; third axillary plates Median plates Inner median plate Outer median plate tegula

Wings’ placement When insect is resting , wings’placement have three types: Open and flat: dragonfly ; some moths; mosquitoes Upright on the back: mayfly ; some butterflies Fore wings cover the back wings: beetles; bugs,grasshoppers

Flying Wing’s movement: up and down; back and forth