Chemical and molecular analysis of the pheromone phenylacetonitrile in desert locust, Schistocerca gregaria Forskål (Orthoptera: Acrididae)

Abstract

The desert locust, Schistocerca gregaria (Orthoptera: Acrididae) is a destructive pest when gregarious but harmless in solitary form. Reports demonstrate the involvement of aggregation pheromones in mediating behavior of the desert locust in the gregarious phase. Phenylacetonitrile (PAN), the major component of the adult aggregation pheromone, can act as an adult aggregant for both sexes and as a male homosexual avoidance pheromone. However, the origin of PAN and its biosynthesis pathway are not well understood. In the present study, chemical and molecular approaches were employed to elucidate the site of production and biosynthesis pathway of PAN. In a previous study, wings and legs of mature gregarious adult desert locusts were shown to emit notable amount of PAN. However, the present study revealed that PAN is widely distributed in body parts of both sexes in varying amounts. This is the first study that detects noticeable amounts of PAN in the body parts of female and suggests that the pheromone is present in both sexes but that the release of this pheromone is restricted to sexually mature adult males. Also, there were significant differences in PAN released by sexually mature gregarious males at various time intervals during photophase (day) and scotophase (night). More PAN was emitted during the photophase than scotophase and there was a positive correlation of PAN emitted with temperature. Sexual receptivity of both sexes in relation to PAN production was determined. These results suggest that both sexes of gregarious desert locusts are involved in mate finding, which may be influenced by sight, age and levels of PAN released by both sexes of adults. Subsequently, forward and reverse subtracted cDNA libraries were created using the suppression subtractive hybridization (SSH) technique. The potential genes encode energy metabolism genes and represent the up-regulated genes that could be responsible for triggering aggregation behavior. Relative expression revealed that the genes were up- and down-regulated in gregarious and solitary phenotypes, indicating that there is a molecular mechanism that switches on and off during phase change and PAN production.