Sexual Maturation and Yellow Coloration of Adult Males in the Gregarious Desert Locust, Schistocerca gregaria, in Relation to Volatiles Emitted (Caelifera: Acrididae)

Abstract

Two strains of the desert locust, Schistocerca gregaria (Forskal 1775) originating from Nigeria and Mauritania, were used to identify locust-borne volatiles emitted by male and female adults as well as to analyse the processes of sexual maturation and yellow coloration. The volatiles were collected at various steps during the adult maturation period. A GC-MS system was applied for separation and identification of target compounds. High-boiling material was collected by washing the body surface of yellow males [MM] with pentane. Significant differences between the head-space extracts of grouped mature MM and females [FF] were reported. Benzyl cyanide [BC] was detected only in grouped yellow MM. Maturation and yellow coloration were found to be independent processes. In the head-space of grouped immature MM, phenol [PH] and guaiacol [GA] were dominant, similarly to what happened with FF. Reduced amounts of both compounds were present in mature insects and BC became dominant in grouped MM. Isolation of yellow MM resulted in a total loss of BC in the volatiles emitted after about one week, but the yellow coloration of the body was maintained. FF did not stimulate BC release, which was induced only by species-specific mature MM and their pentane surface extract. Yellow MM were able to accelerate the yellow coloration of grouped immature MM, which could neither be achieved by the application of BC alone, nor by the volatiles present in the locust breeding room and by mixtures of volatiles. Pentane cuticle extracts from yellow MM accelerated the synchronization of maturation in both sexes, in the same way as yellow MM did.