Development of a Phytochemical-Based Lure for the Dried Bean Beetle Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae)

The dried bean beetle, Acanthoscelides obtectus, is an economically important, worldwide pest of legume crops including dry beans, Phaseolus vulgaris. Assessment of A. obtectus infestation levels in pre-harvest field crops and post-harvest granaries is difficult to achieve because there is no effective monitoring tool for early detection so that interventions can be deployed as needed. Because A. obtectus is a generic pollen and nectar feeder, we adopted an electrophysiological (EAG) screening approach, using the antennae of female A. obtectus to identify physiologically active, volatile phytochemicals, which could then be investigated for their attractiveness to A. obtectus in laboratory behavioral assays and preliminary field tests. Of the 27 compounds tested in EAG screening, 5 compounds, i.e., methyl anthranilate, methyl eugenol, benzyl alcohol, (RS)-lavandulol, and 2-phenylethanol, elicited stronger EAG responses than the standard (1-phenylethanol). In 4-arm olfactometer bioassays, female A. obtectus preferred the olfactometer arm containing the odor of either methyl anthranilate or benzyl alcohol compared to the solvent control. In preliminary field tests using these 2 compounds as a binary mixture, at least 5 times as many beetles were caught on baited traps compared to non-baited traps. The field data also suggested that benzyl alcohol was primarily responsible for the field activity of the blend. We hypothesize that the attraction of A. obtectus to the combined benzyl alcohol/methyl anthranilate and the single benzyl alcohol baits is connected to the species` nectar- and pollen-feeding behaviour and not to its intraspecific communication. To our knowledge, this is the first evidence that A. obtectus behavior in the field can be modified by the deployment of plant-derived semiochemicals.