Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2016
Publication Date: 3/1/2017
Citation: Njoroge, A.W., Affognon, H., Mutungi, C., Richter, U., Hensel, O., Rohde, B., Mankin, R.W. 2017. Bioacoustics of Acanthoscelides obtectus (Coleoptera: Chrysomelidae: Bruchinae) on Phaseolus vulgaris (Fabaceae). Florida Entomologist. 100(1):109-115.
DOI: https://doi.org/10.1653/024.100.0116

Interpretive Summary: Bean weevils are important economic pests of stored beans and other legumes in sub-Saharan Africa. Scientists at the USDA, Agricultural Research Service, Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, Florida, in collaboration with the International Centre of Insect Physiology and Ecology, Nairobi, Kenya, the University of Kassel, Witzenhausen, Germany, and the University of Florida, Gainesville, Florida, investigated sounds produced by larval and adult weevils in beans. It was found that both adults and larvae could be detected easily and that adults produce sounds with different temporal patterns than the larvae. The use of acoustic sensors can be helpful in identifying infestations of internally feeding weevils in beans and can help reduce the economic damage caused by hidden insect pests to farmers and agribusiness in sub-Saharan Africa.

Technical Abstract: Acanthoscelides obtectus (Say) (Coleoptera: Chrysomelidae), is an economically important pest of common bean Phaseolus vulgaris L. (Fabaceae) in the tropics and subtropics. It is difficult to detect the presence of A. obtectus because the larvae are cryptic and spend most of their developmental time inside the bean seeds. Their presence is almost imperceptible except for circular emergence holes created by the last instar larvae as they exit as adults. We considered a hypothesis that readily available acoustic means can be used to detect these larvae. Laboratory experiments were conducted in an anechoic chamber to estimate the acoustic characteristics of A. obtectus larvae and adults on stored common beans. The larvae displayed continuous low-amplitude insect sound impulses frequently occurring in trains (bursts) of two or more impulses (mean = 3.6). In contrast, the adults displayed lower-amplitude impulses with shorter bursts. The rates of bursts and the impulses per bursts for the larvae and the adults were significantly different (P = 0.05). Overall, the larvae and adults of A. obtectus produced varied acoustic signals of utility for real-time detection of A. obtectus infestation in stored common beans in sub-Saharan Africa. The use of such technology in the future, especially if its costs can be reduced, may contribute to efforts to alleviate hunger and poverty in the region.