Evaluation of resistance to insecticides in the mosquito larvae of Anopheles gambae Giles and its control by microbial bacterial pathogens

Abstract

It was found that resistance factors of mosquito larvae were near unity for dieldrin, and 2 to 3 times for Malathion at both Ahero and Mwea, and 2 times for DDT at Ahero. These low resistance factors indicated little or no resistance by the mosquitoes to these insecticides. However, resistance factors to fenitrothion at Ahero of times 30.5 and at Mwea of times 5.4, and to DDT at Mwea of 16.5, were high indicating resistance to these insecticides. This was explained by the fact that these 2 insecticides have been regularly used for rice pest control, and therefore, the mosquitoes had become used to them. Comparative bioassays showed that younger active larval instars were most susceptible to these bacterial pathogens as determined by both spore counts compared to international toxic unit system methods for measuring toxicity of the bacterial isolates. Although the toxic activity of the bacterial formulations was reduced under field condition, it was concluded that this method of control could be an effective alternative for the management of malaria vector mosquitoes in rice irrigation schemes