The larvicidal activity of two entomopathogenic bacteria Bacillus thuringiensis H-14 and B. sphaericus 1593 against mosquito larvae of Culex pipiens has been evaluated. According to LC50 values obtained, B. thuringiensis (4.6 x 105 spores/ml) proved to be highly pathogenic to fourth instar larvae than fi. sphaericus (4.2 x 106 spores/ml).

Larval treatment with LC50 levels of both pathogens affected the reproductive potential of surviving adults during two successive gonotrophic cycles. These treatments caused insignificant changes in some basic morphometric characteristics of mosquito females that developed from surviving larvae.

The larvicidal activity of the pathogen Bacillus thuringiensis H-14 against mosquito larvae of Aedes aegypti (L.) and Culex pipiens L. has been evaluated.

The results showed that the susceptibility of culicine larvae to this pathogen was closely correlated with mosquito species tested and its larval instars. The toxicity curves indicated that the serotype H-14 had a higher pathogenicity against A. aegypti than C. pipiens. LC50 values showed that, for both mosquito species tested, the second instar larvae were more susceptible to the pathogen used than the fourth instar larvae.

Apart from lethal action, larval treatments with B. thuringiensis H-14 led to a decrease in the reproductive potential of female mosquitoes that emerged from these treatments.