Isolation, characterization and evaluation of potency of native bacillus thuringiensis against maize insect pests and aflatoxin producing fungi

Abstract

Bio-control of pests using Bacillus thuringiensis represents the most potential use of biological control agents to date. Among major constraints to maize production, safety and hence food sufficiency in Kenya is infestation, damage and contamination by insect pests. Maize grains are adversely damaged by Prostephanus truncatus which occasionally paves way for the growth of aflatoxin producing fungi. A number of management strategies have been employed for the control of maize insect pests including the use of synthetic insecticides all of which however, have limitations. The focus of this study was to isolate and establish the efficacy of native B. thuringiensis against P. truncatus, Chilo partellus, Aspergillus jlavus and Aspergillus niger for use in both pre-harvest and post harvest maize protection. The isolated B. thuringiensis strains were classified according to their morphological appearance, growth and biochemical characteristics. Based on the preliminary potency tests, isolates KG 411, KG 12-0, KG 20, KG 420, KM 31 and KM 24 caused over 50% mean mortality at the first predetermined discriminate dose of 10 mg/m\. With subsequent log probit analysis KG 411 was significantly more toxic at 95% confidence limit (p <0.001) than all the other isolates, with a median dose of 0.30 mg/ml causing 77.1% mean mortality. Log probit analysis for toxicity of the native B. thuringiensis isolates on the second instar larvae of C. partellus showed significant differences at 95% confidence limit (p<0.00 1), with isolate KM 12causing the highest mean mortality of 76 %. Evaluation of effects of the B. thuringiensis isolates against the above mentioned two fungal strains showed that isolate KM 31 was the most inhibitory, causing 83.33 % and 78.33 % inhibition against A. niger and A. jlavus respectively at 95% confidence (p < 0.001). In conclusion, this result demonstrates the availability of novel native B. thuringiensis which would constitute an alternative biological control option for management of adult P. truncatus, A. niger and A. jlavus III both pre-harvest and post harvest maize protection.