Bacteria inhabiting the gut of insects provide many benefits to their hosts, such as aiding in food digestion, reproduction, and immunity, tissue homeostasis, adaptation to environment and resistance to pathogen and pesticides. The cowpea beetle, Callosobruchus maculatus , is a serious cosmopolitan pest of pulses. This beetle has lent itself as a guinea pig for several ecological studies. It harbors a consortium of bacterial communities in its gut, but the evidence for their role in its physiology is fragmentary. In this work, we hypothesized that gut microbiota mediates C . maculatus resistance to dichlorvos (DDVP or O , O -dimethyl O -2,2-dichlorovinylphosphate) and represent the target of Lippia adoensis (Gambian Tea Bush) essential oil (EO). Symbiotic and aposymbiotic beetles were exposed to artificial cowpea seeds earlier treated with DDVP or EO. Adult mortality and changes in gut bacterial community composition and abundance were examined at F 1 and F 5 generations. The susceptibility of experimental beetles to DDVP was significantly affected by their symbiotic status. The adult mortality decreased across generations in DDVP treatments, and remained significantly higher in aposymbiotic groups. In EO treatments, the mortality was consistent irrespective of symbiotic status and experimental generations. When compared to DDVP and the Control, EO treatments had significantly lower bacterial richness and diversity, as well as lower abundance of Proteobacteria, Firmicutes, and Bacteroidetes. These results support our hypothesis and describe the responses of gut microbial communities to pesticide treatments. This could be of interest for developing new management strategies of this pest.

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The resistance status of Nigeria populations of Callosobruchus maculatus (Fab.) to dichlorvos (2,3 -Dichlorovinyl dimethyl phosphate {DDVP}) was investigated in the present study. Bruchids were obtained from five different locations spread across three South-Western states of Nigeria. These include Akure (Ondo state), Ikare-Akoko (Ondo state), Ikere-Ekiti (Ekiti state), Ijan-Ekiti (Ekiti state) and Ibadan (Oyo state). A susceptible laboratory culture of C. maculatus served as the reference population. Bruchid populations were exposed to filter papers impregnated with DDVP (concentration range: 0.00001% -0.01%) and the mortality was assessed after 3, 6, 24 and 48 hours post-treatment. Bruchid mortality varied across locations, DDVP concentration and exposure time. Bruchids obtained from Ibadan required the highest concentration (LC 95 : 185.418 mg ml -1 ) of DDVP, hence they have the highest resistance factor (RF) (RF 95 : 1483.30); while their counterparts from Ijan-Ekiti required the lowest concentration of DDVP (LC 95 : 0.242 mg ml -1 ) with the lowest RF (RF 95 : 1.94). The present study reveals diverse levels of resistance to DDVP in Nigerian populations of C. maculatus.Hence, there is a need for resistance management strategies on the use of DDVP and other organophosphate insecticide in its class across various Nigerian states to minimize cost and health risk implications that could arise from insecticide resistance.