Insect wing, Modifications and Copulation

INSECT WING, ITS REGIONS, VENATION AND MODIFICATIONS

v  Insects have a pair of wings in thorax.

v  Wings are located dorso-laterally between the nota and pleura of the meso- and meta-thoracic segments.

v  The wing bearing segments (meso- & metathorax) are called pterothorax.

Wing venation

            The arrangement of veins in the insect wing is called wing venation. Each wing consists of a thin membrane supported by a system of thickened tubular veins. The membranous area between the veins is called cell. The veins strengthen the wings and give rigidity besides aiding blood circulation. Insect wing consists of longitudinal (principal) veins, which runs along the length, and cross veins, which connects the longitudinal veins.

A hypothetical wing will have the veins as follows:

Longitudinal veins/ principal veins	Cross veins
Costa (C) Sub-costa (SC) Radius (R) Median (M) Cubitus (Cu) Anal (A)	humeral (h) radial(r) sectorial(s) radio-medial (r-m) medial (m) medio-cubital (m-cu) cubito-anal (cu-a)

Regions

            Insect wings can be differentiated into many regions. The distal portion of the wing supported by veins is called remigium, while the proximal portion at the base is axillary region / axilla. Below the remigium and in proximity with the basal region are two flexible regions called vannus and jugam. Remigium and vannal lobe or anal lobe is separated by anal or vannal fold, while jugal fold separates vannal lobe and jugal lobe.

Margins

            The anterior margin of insect wings is called coastal margin, the posterior margin beyond remigium is the apical margin, while the jugal and vannal margin constitute the anal margin.

Modifications of insect wings

Modification	Description	Example
Tegmina	Thick and leathery	Forewing of cockroach, grasshopper
Elytra	Sclerotized and horny	Forewings of beetles
Hemelytra	Basal half thick and distal half membranous	Forewings of plant bugs
Halteres	Knob like, at the base sensory cells (Hick’s papillae) & scapal plates present	Hindwings of house fly, forewings of stylopids
Fringed	Bristle like, feathery	Thrips

Pterostigma: Dragonflies and damselflies have a dark rectangular spot along the coastal margin of the fore and hind wings called stigma / pterostigma.

Scales: The wings of butterflies and moths are covered by tile like structure called scales, in an overlapping arrangement. These wing scales are responsible for the bright, attractive, multi-varied coloration in butterflies and moths.

Wing coupling

            In insects, both the fore and hind pairs of wings are closely associated or linked as a single unit, to achieve an efficient flight. This is called wing coupling.

Types of wing coupling

a)    Amplexiform: The broad fore and hind wings are basely overlapping each other. Eg. Swallow tail butterfly

b)    Frenate: large bristles (frenula) of the hind wings interlock with downwardly curved hook (retinaculam) of the forewing. Eg. Fruit sucking moth.

c)    Jugate: A long and finger like structure (fibula) arising from the jugal lobe of forewings lies on the coastal margin of the hind wing during flight. Eg. Few primitive lepidopterans

d)    Hamulate:  A row of curved small hooks (incurving hooklets) called the Hamuli is present along the coastal margin of the hind wing that interlocks with the thickened anal margin of the forewing. Eg. Honey bees.