A male-produced aggregation pheromone facilitating Acalymma vittatum [F.] (Coleoptera: Chrysomelidae) early-season host plant colonization

We conducted field studies to investigate the involvement of volatile cues in early-season host plant colonization by striped cucumber beetle, Acalymma vittatum (F.) (Coleoptera: Chrysomelidae). Wind-directed traps were baited with male or female A. vittatum, potted cucumber (Cucumis sativus) seedlings that were of near-isogenic lines which either contained or lacked cucurbitacin, or combinations of male or female A. vittatum feeding on one or the other cucumber variety. We found no response to undamaged plants of either cucumber variety or plants that were actively being fed upon by A. vittatum females, whereas the response to volatiles associated with male A. vittatum was strong. Both male and female conspecifics and totals of up to sevenfold the number of males in the trap lures were caught overnight. Feeding males attracted more than double the number of conspecifics that responded to nonfeeding males. Active consumption of cucurbitacin in the plant on which the males were feeding, however, had no effect on attraction. A shift in sex ratio from a male to a female bias during field colonization season also supports the hypothesis that host finding is initiated by pioneer males. The importance of this aggregation pheromone in early-season host plant colonization and the evolutionary and adaptive significance of this pheromone are discussed.