Callosobruchus maculatus (Fab.) (Coleoptera: Chrysomelidae) infestation and tolerance on stored cowpea seeds protected with Anchomanes difformis (Blume) Engl. extracts

The study was conducted to evaluate the infestation and tolerance of Callosobruchus maculatus to stored cowpea treated with Anchomanes difformis extracts.

Different concentrations of A. difformis extracts were admixed with 20g of uninfested cowpea seeds in 250ml plastic dishes. Ten unsexed adult C. maculatus were released into each treatment and toxicity was assessed at 24 hrs interval days after infestation, number of eggs laid on cowpea seeds was counted. At the end of the experiment, seeds were reweighed, number of emerged adult and damaged seeds were recorded.

All extracts were significantly toxic to C. maculatus as concentration increased. Ethyl acetate (EA) extract exerted highest mortality ranged 90-100%, while methanol recorded highest longevity. Maximum reduction in egg laid was observed with EA extract (51.44-74.45%), followed by methanol extract at 100 (58.69%) and 150 µl (69.56%). While maximum adult emergence inhibition was observed at 150 µl (93.33%) with EA. Cowpea seeds in control dishes suffered the heaviest infestation (31.76%) compared to EA and acetone extracts that recorded zero infestation at 100 and 150 µl concentration respectively. Susceptibility of cowpea seeds treated with extracts was significantly lower compared to control with 100%infestation.

No hindrances was encountered during the study.

The study revealed that A. difformis possesses oviposition deterrent and adult emergence inhibition properties against C. maculatus that can be utilize for the management of C. maculatus in stored cowpea seeds. Further studies are recommended for exploring the active compound responsible for its insecticidal activities and toxicological effect using albino rats as a model.