Introduction

Although flight energetics figure prominently in the ecology of insect migration, direct measurements of metabolism are not available for any migratory insect in free flight. Quantitative analysis of migratory energetics must therefore be approached indirectly. However, there are few data on the aerodynamic and biomechanical processes of migratory flight; even such basic kinematic parameters as airspeeds and wingbeat frequencies are generally unknown. Aerodynamic studies of migratory flight are of particular use in estimating the mechanical and metabolic power required to fly and these biomechanical analyses can elucidate the implications of morphology and flight behaviour for overall migratory performance. For insects that migrate on ambient winds, aerodynamic evaluations of flapping flight are of less significance, but migration within the flight boundary layer (sensu Taylor, 1958) is widespread in insects and an understanding of the biomechanics of wing flapping is essential for estimating the energetic costs of powered flight. Ultimately, such studies can be integrated with behavioural and environmental data for interpretation of the physiological ecology of migration.

Pennycuick (1969) presented the first detailed analysis of migration mechanics in birds (see also Pennycuick, 1978) and this treatment has recently been extended by Rayner (1990) to incorporate recent findings on the structure of vortex wakes for flying vertebrates. In insects, aerodynamic analyses of migratory flight are less well developed, primarily because the requisite kinematic and morphological data have been lacking.