A new experimental approach to investigate migration in Pieris brassicae L.

.1 It is possible to correlate distinct sequences of flight behaviour in caged females of the migrant butterfly Pieris brassicae with the main flight direction of released individuals of the same stock. The attempts to escape out of the cage point to the same mean direction as the flights of the released butterflies. This provides an experimental tool to investigate some unsolved questions concerning migration behaviour. 2 This study examines the constancy of the flight direction of a group of butterflies, the specificity of the direction in two populations of different geographical origin, and the frequently reported change in flight direction of subsequent generations. 3 The results indicate that the main flight direction of a tested group is very constant during 2 days of observation. Different directions have been detected in populations originating from Northern Germany and Southern France, respectively. The preferred directions are discussed as an adaptation to the geographical circumstances. Subsequent generations of the population from Northern Germany also show different directions. The spring generation flies to the north, the autumn generation in the opposite direction. This result corresponds to field observations that in P.brassicae a return flight occurs in subsequent generations of a year.