Isolation and Identification of Bacillus thuringiensis from Harpaphe Haydeniana and its Entomotoxic evaluation against Aedes and culex larvae

This study was designed to isolate and identify Bacillus thuringiensis from dead Diplopods (Harpaphe havdeniana) and to evaluate its entomotoxicity to Culicidae larvae, Aedes and Culex. Twenty-three (23) viable colonies were selected and characterized through morphological, physiological, cellular, biochemical and antibiotic sensitivity reactions and observations. Only six (6) isolates were presumptively identified as B. thuringiensis as indicated by its endospores that causes toxicity against various kinds of insects. Entomotoxicity activity of the isolates was evaluated by selective bioassay through dose mortality response of different bacterial densities to Aedes and Culex. McFarland Turbidity standards (0.5, 1, 2, and 3) was used to indicate cell count concentrations. Average mortality rate of both larvae was determined through 50% mortality. Only two (2) presumptively identified strains labeled as IF7 and IF15 were entomotoxic. Determination of toxicity was measured by the assessment o f lethal median concentration (LC50) to both larvae in the minimum hour of observation. Results showed that both isolates exhibited higher mortality rate to Culex than on Aedes larvae. Similarly, lethality rate was more evident to Culex than Aedes based on LC 50 . Final evaluation was done through tests between subject effects (ANOVA). Significant differences between the different bacterial densities and control was indicated and showed that isolate IF7 and IF15 shows efficacy only to Culex larvae.