Dispersive behaviour of larvae of the common cabbage butterflyPieris rapae crucivora

To investigate the aggregative nature of the larvae of Pieris rapae crucivora, each 50 individuals of the 4th and 5th instar larvae collected from cabbage farms and reared under crowded and solitary conditions were released on an experimental arena and their dispersive behaviour was observed with the lapse of time. Both the 4th and 5th instar larvae showed the trend to approach toward random distribution when they were released under clumped condition, and they maintained random distribution when they were released at random. Therefore, it may be concluded that the larvae have not any aggregative nature caused by the mutual attraction among individuals. However, as the larvae reared in crowds sometimes showed the slight aggregative behaviour, it seems that the larval dispersal is different between densely and sparsely populated plants in field.