AN ANALYSIS OF THE BEHAVIORAL-EFFECTS OF CROWDING AND RE-ISOLATION ONSOLITARY-REARED ADULT DESERT LOCUSTS (SCHISTOCERCA-GREGARIA) AND THEIR OFFSPRING

The time-course of behavioural change in response to crowding and re-i solation was investigated in adults of Schistocerca gregaria Forskal ( Orthoptera, Acrididae) using logistic regression analysis. Crowding so litary-reared adults for a period of 4 h caused them to behave similar ly to crowd-reared insects, with their becoming much more active and m oving towards rather than away from a stimulus group of locusts. Respo nsiveness to crowding was greatest in young adults. The behaviour acqu ired after 48 h of crowding was lost within 1 day of re-isolation. Alt hough experience by solitary-reared adults of crowding for 48 h had on ly transitory effects on their own behaviour, there was also a long-te rm influence on the behaviour of their offspring. The strength of this effect was dependent on the age at which adults experienced crowding, increasing in a graded manner with adult age, and hence the recency o f crowding before oviposition. Parents crowded at a late stage in the reproductive cycle yielded hatchlings which behaved indistinguishably from those from crowd-reared adults. Such an effect is consistent with the idea that females, through their previous experience of crowding, are effectively predicting the probability that their offspring will emerge into a high-density population, and predisposing their hatchlin gs' behaviour accordingly.