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Teretrius nigrescensis considered to be a specialized predator of Prostephanus truncatus, a serious pest of stored maize and dried cassava roots. Using a bait-bag behavioral bioassay, this investigation found T. nigrescensto be strongly arrested by dust and frass produced by P. truncatuson maize, whereas responses to maize flour were weak. Attempts to increase the arrestiveness of flour by altering its physical properties (coarseness or particle size range) were unsuccessful. The arrestive property of dust/frass did not degrade with long-term storage nor did it volatilize or degrade with oven baking up to 150°C. However, extraction with methanol and reapplication was successful in transferring the arrestive property from the dust/frass onto maize flour. The prey dust/frass also induced more oviposition than did maize flour, as judged by production of F1 offspring. The results provide strong evidence for the existence of a high boiling point compound(s) in P. truncatusdust/frass that acts as a contact kairomone for T. nigrescens. This, or another compound(s) also seems to act as an oviposition stimulant for female T. nigrescens.

Male Rhyzopertha dominica (F.)(Coleoptera: Bostrichidae) release an aggregation pheromone consisting of a blend of two components, dominicalure 1 (D1) and Dominicalure 2 (D2). Pheromone from single insects, in different contexts, was collected and measured to determine if this signal is phenotypically plastic. Release rates were lowered when males were moved from maize grains to groundnut kernels or when moved from solitary occupation of maize grain to grain occupied by seven females. The pheromone release was increased again once these moves were reversed. The release of D1 was more affected than D2: thus, on groundnuts or in the presence of females, less pheromone was released and the proportion of D1 in the blend was lowered. Possible reasons for the modifications of the signal are discussed.

Intermale variation in pheromone signaling has been confirmed and quantified by measurements of pheromone produced by single adult male Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae). Males varied in both the amounts of the two components of their aggregation pheromone and the ratio of one component to the other. The mean rates of production of the pheromone components T1 and T2 were 1.9 and 0.5 μg/day, respectively. There were repeatable differences among males in the amounts of T2 produced and the proportion of T1 in the pheromone blend over two weeks. Of the 15 males studied, one released a large burst of pheromone in a short period, while the remainder, if they did release, did so over an extended period. This suggested that there may be two alternative release strategies and the significance of this is discussed.

The ability of both male and female Prostephanus truncatusbeetles to distinguish between the aggregation pheromone signals of two closely located conspecific male beetles was investigated by using an olfactometer. Beetles detected variation between male signalers and visited some signalers more than others. Beetles of both sexes were found to make the same choices. These patterns of preference were found to be mirrored in trap catches of dispersing beetles when single males were used to bait flight traps that were placed in pairs in a woodland habitat in Ghana. The results are discussed with reference to the hypothesis that males signal primarily to attract mates and, therefore, features of the aggregation-pheromone signal may be sexually selected. The implications of the results for current and possible future pest-management tools are also explored.