The responses of Prostephanus truncatus (Coleoptera: Bostrichidae) and Sitophilus zeamais (Coleoptera: Curculionidae) to pheromone and synthetic maize volatiles as lures in crevice or flight traps

Flight traps and crevice traps for catching Prostephanus truncatus (Horn) and Sitophilus zeamais Motschulsky were studied in Kenya. The traps were baited with pheromones of these beetles, with or without synthetic maize volatiles. Ln the case of P. truncatus, which has a two component pheromone consisting of Trunc-call 1 (T1) and Trunc-call 2 (T2), the components were tested singly or in a 1:1 combination. The addition of synthetic maize volatiles to pheromone traps did not result in an increase in trap catch of either S. zeamais or P. truncatus. The pheromone of S. zeamais was an effective lure in both crevice and flight traps but the actual numbers captured were low. Captures with traps baited for P. truncatus were much greater. The response of P. truncatus to the two components of its pheromone was affected by the type of trap used. Crevice traps baited with either component alone caught fewer beetles than those baited with a mixture. in contrast, flight traps baited with T2 or the mixture were equally effective while traps with only T1 caught significantly fewer than either of these. These observations clarified apparent discrepancies between earlier studies in Tanzania and Mexico and are used to derive an hypothesis about the roles of T1 and T2; T2 appears to be a long-range attractant and T1 important for modifying the response to T2 to facilitate close-range orientation. Adult P. truncatus arriving at the traps were sexed, and in both flight and crevice traps the majority of captures were females even though in the experimental maize cribs the beetles were present in a roughy equal sex ratio. The role of the pheromone is discussed in the light of this observation.