Resistance of the house fly to Bacillus thuringiensis Berliner

Abstract

Resistance to Bacillus thuringiensis Berliner was induced in house flies (Musca domestica Linnaeus) by selecting survivors from treated larval medium during 50 generations of rearing. The degree of resistance, based on the ratios of LD50 values, varied from 8- to 14-fold between the 27th and 50th generation, inclusive. Resistance, developed during 30 generations of selection, appeared to decline slightly during 20 generations without selection pressure. A wild strain subjected to 10 generations of selection did not become more resistant than a laboratory strain with comparable selection. Early and late pupating strains of house flies, with larval periods of 5 and 8 days, respectively, were equally susceptible. As the age of larvae increased from 1 to 4 days, the LD50 values increased from four- to sixfold with each additional day larvae were reared in the absence of spore powder. Mortality occurred primarily in the larval stage when tests were initiated with eggs, and it occurred mainly in the pupal stage when tests were initiated with 2-day-old larvae. The relative increase in LD50 values was the same for both resistant and susceptible strains of house flies when spore powder was autoclaved.