Abstract

Migratory locust, Locusta migratoria (Orthoptera, Acrididae) changes phase in response to population density. By rearing nymphs from a solitarious (isolated-reared) and gregarious line at three different densities, we examined the effects of rearing density on body coloration and morphometry at the last nymphal instar, adult stage and hatchlings of the subsequent generation. Changes in density lead to phase transformation shown by a shift in the body coloration and size to either direction depending on population density. Nevertheless, the complete shift of solitarious locusts to gregarious phase cannot be acquired in the first generation of crowding and solitarious body coloration still appears even at high density (100 locusts/cage). In both phases, the shift of body colour in response to the variation of population density was more rapid than the morphometry. Adult rearing density affected also the progeny body colour and size. However, the parental prehistory and the environmental conditions of the offspring were also important to modify the phase characteristics. The most important gregarious characteristics of hatchlings (black body colour and large size) were observed if parents were maintained at the density of 40 per cage. These characteristics depend not only on parents phase state but also depend on the food abundance. We found a positive correlation between the darkness of body colour and size of hatchlings and this effect was more pronounced in gregarious line.

Key words: Locusta migratoria, rearing density, phase characteristics, progeny, parents’ prehistory.