Larvicidal Activity of <i>Bacillus sphaericus</i> Strain SI-1 and Its Toxins against <i>Culex quinquefasciantus</i> Larvae

Abstract

A local isolate of Bacillus sphaericus strain SI-1 had been investigated for its larvicidal activity against Culex quinquefasciantus mosquito. Wet spores of 72-h grown culture of the strain were sufficiently potent as mosquitocidal agents 3rd instar larvae of C. quinquefasciantus. After lyophilization the toxic potency of the strain increased sharply (165 times). The toxic crystal proteins had been solubilized in a hydroxyl-chloride buffer (pH 12.0) by three successive extractions. The majority of the proteins were found to be solubilized in water under these conditions. Increase of pH in the media by addition of buffer and its effect on the mortality of C. quinquefasciantus larvae had been checked. The extraction buffer was found to be non-lethal although significant rise in pH up to 10.44 was observed. The lethal concentration fifty (LC50) value of the crude protein was found to be 62.0 μg/ml.

Keywords: Bacillus sphaericus SI-1, Biopesticide, Culex quinquefasciantus, Larvicidal activity, Lyophilization

DOI: http://dx.doi.org/10.3329/bjm.v24i2.1256

Bangladesh J Microbiol, Volume 24, Number 2, December 2007, pp 125-128