1

Introduction

5

these function as a perfect mechanical spring. During flapping, movements

occur either at low, medium or high frequencies. It may be noted that insects

cannot fly if the resilin gets damaged or dissected. The resilin helps in wing

folding at rest.

(2)

A large number of longitudinal veins are present within the wing which

strengthen the wing membrane. The venation pattern of wings differs from

order to order in insects. Venation also plays an important role in insect clas-

sification and identification at various levels. Aeroelastic effects in moving

flexible wings are mainly responsible for developing structural deformations

and aerodynamic forces which contribute to the flight.

(3)

Wing venation and resilin influence the aeroelasticity of the wings signifi-

cantly during flight by way of axial stretching, buckling and resulting damped

vibrations. This needs further study.

(4)

The wing membrane is formed by two thin layers of integument which are

sandwiched and enclose the trachea, nerve, haemolymph and veins.

(5)

Resilin present at the wing base is four times more elastic than natural

rubber. It stores up to 80% of potential energy during its wingbeat. It is

an important protein-based elastomeric biomaterial. Resilin has 100 times

higher storage capacity for elastic energy than muscle. It does not undergo

fatigue as compared to muscles.

(6)

The direct and indirect muscles of the thorax play a major role in insect

flight. The indirect muscles, i.e., Dorso-Longitudinal Muscle (DLM), span

the tergum. Dorso-Ventral Muscles (DVM) extend from tergum to sternum.

The direct muscles are attached to pleuron and sclerites at the wing base.

(7)

Direct flight muscles are attached to the wing base of mayflies and dragon-

flies which are primitive insects. Indirect flight muscles are generally well

developed in advanced insects like honey bee, housefly and plant bugs, and

they are attached to the thorax.

(8)

In mayflies and dragonflies, a small downward movement of the wing base

lifts the wings themselves upward. Indirect flight muscles are attached to the

thorax. The deformation of the thoracic tergum leads to the movement of

the wings. This partly explains the role of direct and indirect flight muscles

during flight.

(9)

There are also accessory indirect flight muscles that help in modifying wing

movements including wing rotation.

(10)

The linear or rotatory wing movements of flapping flexible wings are quite

complex. Approximately, a figure of ‘8’ is traced at the wingtips, which can

be observed through a stroboscope in Cicada, soapnut bugs and house flies.

(11)

Generally, large insects like dragonflies, cockroaches, grasshoppers, butter-

flies and moths have larger wings exhibiting a low wingbeat frequency.

Smaller insects like mosquito, housefly, drosophila, etc. flap their wings at

high wingbeat frequency (250–1000 Hz). During hovering, wingtips trace a

figure of ‘8’.