DEVELOPMENT OF A HIGH-LEVEL OF RESISTANCE TO BACILLUS-SPHAERICUS IN AFIELD POPULATION OF CULEX-QUINQUEFASCIATUS FROM KOCHI, INDIA

Field resistance to Bacillus sphaericus was observed in a population o f Culex quinque-fasciatus in Kochi, India, exposed to 35 rounds of spr aying with a formulation of B. sphaericus 1593M over a 2-year period. Larvae from the sprayed area gave LC(50) and LC(90) values that were 1 46 and 180 times greater than corresponding values for a susceptible s train from an unsprayed locality. When the resistant strain was coloni zed in the laboratory and subjected to moderate selection pressure at each generation, resistance rapidly increased and by the 18th generati on it was 6,223 and 31,325 times greater at the LC(50) and LC(90) leve ls in comparison with the susceptible strain. There were no significan t differences among 6 susceptible strains tested. Tests were repeated and validated using the standard primary powder SPH88, B. sphaericus 2 362. No cross resistance was observed against B. thuringiensis H-14.