A GREGARIZING FACTOR PRESENT IN THE EGG POD FOAM OF THE DESERT LOCUSTSCHISTOCERCA-GREGARIA

The behavioural phase state and coloration of hatchling Schistocerca g regaria were examined in a series of experiments to determine the mean s by which phase characteristics are passed between generations, Both crowding of solitary-reared females at the time of oviposition and hig h egg pod densities promoted behavioural gregarization, although the f ormer appeared to be a rather more potent factor, In contrast, egg pod density alone appeared to promote the development of hatchlings with dark patterns characteristic of the gregarious phase, The phase charac teristics of hatchlings were unaffected when sand previously used for oviposition was used to collect further egg pods, Early separation of presumptive gregarious eggs from egg pods laid by crowd-reared females led to solitarization of the hatchlings, indicating that a factor, ei ther in or around the eggs, removed by early separation promoted grega rization, Both the eggs and foam plugs of egg pods from crowd-reared, gregarious females appeared to be a source of this gregarizing factor, In contrast, there was no evidence for a solitarization factor in egg pods from solitary-reared S. gregaria. Saline extracts of egg pod foa m plugs produced an active factor which promoted gregarization both in eggs from solitary-reared females and in eggs from gregarious females which were separated and washed to removed the factor, Solitary eggs were influenced by the gregarizing factor in foam plug extracts for up to 1 day after oviposition, Saline extracts of foam plug retained the ir activity for up to 1 day, Initial studies on the properties of this factor were made, We conclude that the foam plugs of egg pods from cr owd-reared, gregarious locusts contain a small (<3 kDa), hydrophilic g regarizing factor which is produced at the time of oviposition and whi ch predisposes hatchlings to attain characteristics of the gregarious phase.