Larvicidal toxicity and parasporal inclusion of native Bacillus thuringiensis BK5.2 against Aedes aegypti

Native Bacillus thuringiensis BK5.2, isolated from soil of Baluran National Park, East Java, Indonesia, has been shown to be toxic against Aedes aegypti larvae. This study aims to determine the strength and the speed of the toxicity of B. thuringiensis BK5.2 against A. aegypti larvae in lethal concentration (LC) and lethal time (LT), as well as detection of toxin structure and parasporal inclusion. LC values were determined by the mortality of A. aegypti third instar larvae after 24 and 48 h exposure to five various concentrations of B. thuringiensis BK5.2, while LT values were determined based on the mortality of A. aegypti third instar larvae due to exposure to LC90 concentration at 0; 0.5; 1; 2; 4; 8; 10; 20; 24; and 48 h. Larvicidal toxicity was determined based on value of LC50 and LC90 (CFU/mL), as well as LT50 and LT90 (hours) analysed with Probit analysis. Parasporal inclusion was detected using transmission electron microscope (TEM) and scanning electron microscope (SEM). Based on bioassay, LC50 and LC90 values were 11.6 × 106 and 22.7 × 106 CFU/mL, respectively, at 24 h exposure, as well as 8.3 × 106 and 15.4 × 106 CFU/mL, respectively, at 48 h exposure, while the value of LT50 and LT90 were 19.0 and 26.6 h, respectively. Morphological observation of the dead larvae showed there was damage on abdomen and thorax region. Detection by TEM and SEM showed there was cuboidal parasporal inclusion. Native B. thuringiensis BK5.2 has high toxicity against A. aegypti larvae and detected flatcuboidal toxin in parasporal inclusion.