A radar and aerial‐trapping study of an early spring migration of moths (Lepidoptera) in inland New South Wales

The migrations of a number of species ofnoctuid and pvralid moths were studied with a specialpurpose radar unit and by direct sampling with a kite‐borne net at a locality in central‐western New South Wales during the early spring of 1980. The observations coincided with the appearance of very large numbers of moths throughout much of south‐eastern Australia, and immediately followed a major caterpillar plague in south‐western New South Wales. The migrations occurred mainly at night, and were most intense during periods of warm weather. Several different directions of migration were observed, but the movements were always approximately downwind; distances of a few hundred kilometres were typically covered during a single night. A number of quantitative measures of the migration intensity have been estimated for some of the flights. The migrating population frequently exhibited a degree of mutual alignment, which was sometimes in a direction different from that of the migration. Migrants became concentrated into layers at high altitudes (up to 1900 m) on two occasions during the night. Similar high‐altitude migrations were also detected during daylight. It is inferred that an early spring re‐invasion of drought‐affected inland areas, and of areas on the continental periphery which have a cool winter climate, by means of long‐distance migrations from inland areas where autumn and winter conditions have been favourable for larval development, is an almost regular feature of the population dynamics of several moth species that are of economic importance in south‐eas‐tern Australia. These migrations are interpreted as an adaptation to the geographie and climatic factors that control larval development and moth flight in this region, and especially to the erratic rainfall regime of the inland source areas.