ABSTRACT

The potentials of fungi; Aspergillus niger and Penici/lium oxalicun, in checking weevils, callosobruchus maculahis (Fab) and Silophiliis zeamais (Molt) in stored grains were investigated. A. niger and P. oxalicum spores and mycotoxins harvested from prepared cultures of these fungi were applied to adults and larvae of these weevils in the stored beans and maize. A. niger spores caused mortalities of 57.33% and 51.00% in adult and larvae oC. macu/a/us respectively. In S. zeamais, 40.67% and 41 .00% mortalities were recorded in adults and larvae. In P .oxalicun, spore treatments 59.67% and 58.67% mortalities were observed in adults and larvae of C. mactila/us while in & zeamais 40.00 and 30.33% mortalities in adults and larvae were obtained. The toxicity of the mycotoxins obtained from broth culture filtrate was assessed at different concentrations. The concentrations 0.5 — 40.0% were observed to affect the activities of the weevils. In adult emergence, A. niger filtrate treatments suppressed emergence of C. macu/a/us at 1.0— 5.0% filtrate concentrations within 7 — 21 days post= treatments and 2.0 — 10.0% concentrations affected S. zeanais emergence within 14 — 21 days post treatments. In P. oxailcum treatments, it was observed to have suppressed adult emergence of C. macu/a/us at 10.0 — 20.0% concentrations within 7 — 21 days post treatment and 10.0% concentration within 5days treatment in S. zeamais In the level of damage caused to stored grains, increased concentration of treatments gave decreased percentage damage for instance 20.0% concentration of A .niger did not allow significant damage in maize just as did 40.0% concentration of P. oxalicum filtrate. In C. macu/a/us, the treatments were significantly different with A. niger at 5.0% concentration (P0.001), while P. oxalicum treatment appeared to be the same in S. zeamais. The level of perforations to the grains was used as confirmatory test to the efficacy of the fungal - toxins on treated grains. The concentrations 5.0 40.0% of A. niger produced the least perforations by C. maculalus within 5 — 21 days post treatments while in P. oxalicuin, it was at 40.0% concentration. For S .zeamais, A .niger is efficient at 2.0 -40.0% within 2ldays post treatment while I'. oxalicum was effective at 10.0 - 40.0% concentration within 14 — 21 days post treatment. For protective action and persistence in grains by the mycotoxins used, the Weevil Perforation Index (WPI) was adopted; (WPI> 50 = negative protectant, WPI< 50 = positive protectant). A. niger toxin gave positive protectant in cowpea from 0.5 — 40.0% filtrate concentration against C .maculaius, in maize, from 2.0 — 20.0% concentration as against S. zearnais. In P. oxalicum treatments, it was from 1.5 — 20.0 for C. maculatus and 10.0 — 40.0 in S. zeamais. The data obtained in this work were transformed using arc-sine in percentage damage, square root transformation in level of perforations, and logarithm transformation in weevil emergence. Transformed values were analysed based on analysis of variance (ANOVA) and DMRT; LSD (0.005). The fungal treatments both as spores and toxins have proved highly effective in the control of grain weevils (P0.001) especially in C. maculalus. In the viability test, 85% germination was recorded in P. oxalicum treated maize and 78% germination in A. niger treatment. In cowpea, 50% germination was observed in I'. oxalicuin treatment and 45% germination in A. luger treatment. In the control measures of the grain weevils based on the market survey, more than 90% of the respondents used chemicals irrespective of their potential adverse side effects. For cost — effectiveness, fungi materials are cheap, sustainable and available as against conventional insecticides.