Insect wings

Studies on Insect wings

1. Structure and modifications of wing venation, modifications and wing coupling apparatus Prepared by Dr. S. Sumaiya

2. Insect wings Two pairs of wings - in pterothoracic segments ( meso - and metathorax ) Only one pair of wings - eg . true flies (house fly, horse fly) No wings ( apterous ) – eg . primitive insects (silverfish, spring tail) Secondarily wingless – eg . Head louse, poultry louse and flea Deciduous wings – eg . Ants and termites

3. Wing venation The principal veins run more-or-less lengthwise on the wing, thus called longitudinal veins . They are connected by cross-veins . A closed area bounded by veins is called a cell . In insects, like dragonfly, damselfly, there is an opaque spot near the costal margin of the wing called pterostigma .  In more primitive insect groups ( Odonata ), the regions between principal veins contain irregular networks of veins. These networks represent the remains of the archedictyon described from insect fossils. These veins (and their branches) are named according to a system devised by John Comstock and George Needham (1898) - the Comstock-Needham System:

4. Longitudinal veins • Costa (C) - the leading edge of the wing • Subcosta (Sc) - 2 nd longitudinal vein, typically unbranched • Radius (R) - 3 rd longitudinal vein, 1-5 branches reach the wing margin • Media (M) - 4 th longitudinal vein, 1-4 branches reach the wing margin • Cubitus (Cu) - 5 th longitudinal vein, 1-3 branches reach the wing margin Anal vein Un branched vein behind the cubitus

5. Cross veins Names of crossveins are based on their position relative to longitudinal veins: c-sc : Between the costa and subcosta r : Between adjacent branches of the radius r-m: Between the radius and media  m-cu : Between the media and cubitus Some crossveins have their own name, like h : Humeral crossvein  s : Sectoral crossvein

6. WING MARGINS Wing is triangular in shape and has three margins and angles. Costal margin : Anterior margin is costal margin. Apical margin : Outer margin is apical margin. Anal margin : Posterior margin is anal margin.  

7. WING ANGLES Humeral angle : Angle at the base of the costal margin of the wing. Apical angle : Angle between the costal margin and the apical margin. Anal angle : Angle between the apical and anal margin.

8. Wing regions The entire body of the wing is divided into basal articular and alar regions. The alar region is divided into three regions -based on the folding of lines and the concentration of veins.   Remigium : The anterior area of the wing supported by veins   Clavus or Vannus : The flexible posterior area is termed as Vannus The two region separated by vannal fold   Jugum : The proximal part of vannus , when well developed is separated by jugal fold . The area containing wing articulation sclerites – Pteralia is called axilla

9. Tegmina : Forewings of cockroach, grasshopper, preying mantis, and earwigs.

10. Elytra : Forewings of beetles and weevils Horny, sclerotized , sheath-like Devoid of veins During flight, they are kept at an angle

11. Hemelytra: Forewings of heteropteran bugs Basal portion of forewing is thickened and leathery (like elytra) Apical/ distal half is membranous Wing blade is divided into 5 regions embolium , corium, cuneus , clavus membrane

12. Halteres : Hind wings of true flies One pair of wing is modified into ‘balancers’. Provides stability during flight. Club shaped - has a basal scabellum , bulbous free end ( capitellum ) and a rod like stem . Scabellum - has 2 large groups of sensory bodies, forming the smaller ‘ Hick’s papillae ’ and large set of scapel plate.

13. Fringed wings: both pairs of Thrips Narrow Membraneous Margins are clothed with long fine hairs

14. Scaly wings: both wings of butterflies & Moths Has unicellular flattened setae, coloured scale like structure Responsible for colouration of the wing

15. Membranous wings Forewing of true flies; hindwing of grasshopper, preying mantids and beetle; and both wings of dragonflies, damselflies, bees and wasps Wing blade is thin, transparent, supplied with a network of veins. Useful in flight

16. Hairy wings

17. TYPES OF WING COUPLING Hamulate : a row of small hooks – coastal margin of the hind wing - Hamuli Engage the folder posterior edge of fore wing Ex: bees Amplexiform : linking structure – absent Coupling achieved by broad overlapping of adjacent margins Ex: Butterfly

18. TYPES OF WING COUPLING Frenate : Fruit sucking moths and Hawk moths

19. Frenate Female frenate : Humeral lobe (near the base of the costal margin) of the hindwings gives rise to a group (2-20 nos.) of bristles called frenulum . It interlocks with retinaculum / catch, composed of several forwardly directed curved hairs on the cubital vein of the forewings. Male frenate : Only a single stout frenular bristle arises on the humeral lobe of the hindwing . It interlocks with the single downward curved spines of the retinaculum present in the radial vein of the forewing.

20. Jugate : Hepialid moths, Sterpsipterans Jugam of the forewings are lobe like It is locked to the coastal margin of the hindwings