Resistance of Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) Populations in Nigeria to Dichlorvos

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.