Evaluation of Resistance Against Bacillus thuringiensis israelensis WDG in Dengue Vector from Lahore, Pakistan

In the present study, resistance against biological insecticide i.e. Bacillus thuringiensis israelensis (Bti) WDG (water dispersible granules) was evaluated in Aedes aegypti larvae. Early 4th instars larvae were collected from the slum area of Misri Shah, Lahore, province Punjab, Pakistan during the period of May 2009 to January 2010. Larval bioassays were carried out with early 4th instars susceptible (laboratory-reared) colony to find out diagnostic dose. A range of known concentrations (100, 40, 20, 10, 5, 2.5 and 1.25 ppm) of Bti WDG was used for fixed time period (60 min). A diagnostic dose of 10ppm was found post 30 min. exposure whereas, the same concentration cause hundred percent mortality of field collected larvae in 60 min. exposure. The resistance level was expressed as resistance ratio (RR) of lethal time for 50% death determined in field collected and susceptible strain. The results indicated that the field collected larvae were 10 times more resistant than susceptible population with respect to dose, while RR LT50 - RR LT90 ranged 1.97-2.22 against Bti (WDG) in Aedes aegypti larvae.