Bioacoustics of Acanthoscelides obtectus (Coleoptera: Chrysomelidae: Bruchinae) on Phaseolus vulgaris (Fabaceae)

Acanthoscelides obtectus (Say) (Coleoptera: Chrysomelidae) is an economically important pest of common bean, Phaseolus vulgaris L. (Fabaceae), in the tropics and subtropics. The larvae are cryptic and spend most of their development time inside the bean seeds. Their presence is almost imperceptible except for circular emergence holes created by the last instar larvae in preparation for their exit as adults. We considered a hypothesis that readily available acoustic detection devices can be used to detect larvae and adults in stored beans. Laboratory experiments were conducted in an anechoic chamber to characterize the sounds of movement and feeding and estimate whether they could be distinguished from background noise in storage environments. The larvae produced low-amplitude insect sound impulses frequently occurring in trains (bursts) of 2 or more impulses (mean = 3.6). The adults produced lower-amplitude impulses, although at a higher rate than the larvae, and there were significantly fewer impulses per burst. These features of the acoustic signals were useful for real-time detection of A. obtectus infestation and discrimination from background noise in stored common beans in sub-Saharan Africa. The use of such technology in the future, especially if its costs can be reduced further, may contribute to efforts to alleviate hunger and poverty in the region.