The production of bioinsecticide using Bacillus thuringiensis

This study aims at determining the ability of Bacillus thuringiensis to induce a biocidal effect on mosquito larvae. The B. thuringiensis used in this work was isolated from soil samples obtained from the root of plantain trees in a garden at Umuoma community in Uli Town. Soil samples were subjected to high temperature of about 50oC in order to exclude other microbes that may contaminate the culture, B. thuringiensis was able to survive the heat condition because they are spore formers. To further enhance purity of the culture, the organism was cultured in Luria Bertani medium which is selective for Bacillus spp. Before the toxicity tests were carried out, various morphological tests such as endospore stain, Gram stain, macroscopic examination and biochemical tests such as starch hydrolysis, oxidase test, motility test, citrate test, methyl red test, indole test, sugar fermentation test and catalase test were carried out to identify the organism. The results showed the isolates to be Bacillus thuringiensis. To ensure the ability of the isolate to produce spores needed for toxicity testing, the isolate was subcultured in nutrient agar and incubated at 37oC for 7 days after which there was formation of spores in the growth medium. The isolate was then inoculated in sterile water containing mosquito larvae in other to test for its toxicity against the mosquito larvae. At intervals, observations were made to determine the rate at which the Isolates induce the lethal effects on the larvae by using the sterile loop to check for viable larva remaining at each set up. The viability is deduced from the ability of the viable larva to retain their motility when agitated with the sterile wire loop. The result for toxicity testing showed that set-up Pr1 had the highest number of dead larvae at 1 – 4 hours respectively, while Gr1 had the lowest number of dead larvae at 1.  Statistical representation of the results showed that there was significant difference of p > 0.05 between time and the parasporal crystals of Bacillus thuringiensis against mosquito larva. Two- factor ANOVA without replication also showed that there was a significant difference between the set-­ups Pr1, Pr2, Gr1 and Db2, and the positive control used gave significant difference of p < 0.05. This study successfully demonstrated the toxicity of the parasporal crystals of Bacillus thuringiensis against mosquito larvae.