EFFICACY OF EXTRACTS FROM HYPTIS SPICIGERA LAM. AGAINST CALLOSOBRUCHUS MACULATUS F. (COLEOPTERA: BRUCHIDAE) IN KERSTING'S GROUNDNUT (MACROTYLOMA GEOCARPUM HARMS)

Abstract

Aqueous foliage extracts from Hyptis spicigera Lam. at 10 and 20 per cent concentrations were applied at 25, 50 and 100 ·C on the seeds of Kersting's groundnut (Macrotyloma geocarpum Harms), to evaluate their bioefficacy against the pulse beetle, Callosobruchus maculatus F. and the effects on viability of the seeds. The experiment was laid out in a completely randomized design with four replications. Data were collected on the infestation and damage caused by the pest, and on the viability of treated seeds. The results showed that the oviposition, progeny emergence, developmental period, adult longevity of the pest, and damage on the seeds were significantly affected by the extract applied. All the extract treatments were found to offer better protection than the untreated seeds in most of the parameters evaluated. Insecticidal efficacy was found to show a dose- and temperature-dependent response. Extracts at 20 per cent concentration, treated at 50 ·C or 100 ·C, offered protection comparable to that of the synthetic insecticide, Pirimiphosmethyl at 20 g kg". Extracts treated at 100 ·C, however, showed significant reduction in the germination percentage of the seeds. The implications of these findings are discussed with the view to developing more sustainable means of protecting Kersting's groundnut grains from bruchid attack so as to minimise the rampant postharvest losses to the crop in the savanna ecology of Ghana.