The bioactivity of three botanical powders in sole and combination against Callosobruchus maculatus (Fab.) was investigated at 29±3°C and relative humidity (R.H.) OF 65+5% in the laboratory. The appropriate mixing ratio of Cymbopogon citratus (C), Alstonia boonei (A) and Hyptis suaveolens involved seven combinations viz., C:A, C:H, A:H, C:A:H, H2:C:A, A:C2:H, H:C:A2 in simple ratios 1:1, 1:1, 1:1, 1:1, 2:1:1, 1:2:1 and 1:1:2. The sole and combinations of botanicals were separately prepared and applied at the concentrations of 1.25% per 20 g seeds of two susceptible cowpea lines viz., Oloyin and IT845-2246 in the Kilner jars. Newly emerged ten females and five males C. maculatus were introduced separately into each of the Kilner jars, and replicated four times in a completely randomized design. Data were collected on adult mortality, number of eggs laid, offspring emergence, percentage seed damage, weight loss and seed viability. Results indicated that powder of H. suaveolens evoked significant mortality (100%) after 7 days of treatment. However, lower means were recorded in oviposition and adult bruchid emergence in cowpea seed treated with powders of H. suaveolens and A. boonei. Likewise, powder of C. citratus recorded the least seed damage and this implied that the three tested botanicals were observed to be effective bio-insecticide. The combination H:C:A2 produced most desirable results causing higher adult mortality (96.33%), low offspring emergence, lower seed damage (0%), higher seed viability (88.00%), and least seed weight loss (0%) and therefore the most bio-active mixing ratio against C. maculatus. There was however interaction and synergism effect among the different combinations.
Key words: Bioactivity, mixing ratio, bio-insecticide, weight loss, viability.
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