Effects of Dennettia tripetalla (Backer), Xylopia aethiopica (Dunal) and Aframomum melegueta Schum Oils against the African Sweet Potato Weevil, Cylas puncticollis (Boheman)

Abstract

Laboratory investigations were performed to ascertain the efficacies of Dennettia tripetalla (G.Backer), Xylopiaa ethiopica (A. Rich) and Aframomum melegueta (K. Schum) for the control of Cylas puncticolis, African sweet potato weevil. Organic solvent extracts of the leaves and fruits of the test plants were separately applied at concentration of 1, 3 and 5% (w/v) for investigation. The biological assays were conducted for six months under ambient temperature, relative humidity (28±3°C, 65±5% RH) and 12Hr light/dark photoperiods; laid out in a completely randomized design with each treatment replicated four times. Results disclosed that 3 and 5% extracts of the three test plants led to significantly (P<0.05) higher mortality of C. puncticollis when compared with 1% and control. 3.75 extract of the tubers. n-hexane extracts of all the test plant products significantly (P <0.05) repelled more than 60% of C. puncticollis within one-hour of exposure. .  Extracts of A. melegueta fruit at 3 and 5% and X. aethiopica fruit at 5% had the most significant (P<0.05) insecticidal activity, followed by extract of D. tripetalla (at 5%). Adult emergence was also significantly higher in control than treated tubers with A. melegueta products giving the lowest significant number of emerged adults. The results of this research demonstrate the efficacies of the test plants extracts for the control of C. puncticollis infesting sweet potato roots during post-harvest storage at the small scale farming level in Calabar, Nigeria.