Abstract

Bacillus thuringiensis is ubiquitous, Gram-positive, spore-forming bacteria that act as a larvicide to various Dipteran species due to the toxin it produce. Sporulation process, the production of endotoxins, of the isolated bacterial strain varies in which some isolates sporulate faster while other isolates took some time for sporulation. Thus, the isolate with faster sporulation process were chosen. In determining the LC₅₀, concentration of the bacterial density was based upon the McFarland standard (4 to 0.5×10⁸ cfu/ml) and 1 ml of bacterial culture was added into cups with twenty (20) Aedes aegypti larvae and was observed for 24 - 48 h. Positive control exhibits lethality at an early hour of inoculation having the highest larvicidal potency with LC₅₀ value of 0.36 cfu (colony forming units)/ml at 24 h and 0.57 cfu/ml at 48 h. Among the different B. thuringiensis isolates tested, toxicity and lethality of the bacterial isolates was only observable after 48 h. Isolates from the garden soil exhibits the highest larvicidal potency with LC₅₀ values of 0.85, 0.97, 0.13, and 0.32 cfu/ml. These results suggested that B. thuringiensis isolated from garden soil is promising as larvicide against the target Dengue virus carrying mosquito.

Key words: Larvicidal, sporulation, colony forming units (cfu), Bacillus thuringiensis, Aedes aegypti.