Development of Resistance in Drosophila Melanogaster by Selective Pressure with Malathion (Organophosphate Insecticide)

Abstract

Two strains o f resistant Drosophila melanogaster were cultured by selective pressure with malathion. One group was exposed to a sublethal concentration for its entire life cycle while the other group was exposed to an LC_65 for twenty- four hours. The data obtained indicates that both strains developed equal degrees of resistance representing a four- fold increase in the LC_50. This appears to be the upper limit of resistance for these flies with respect to their genetic limitations. It is possible, however, that this represents a plateau of resistance and further selection might have caused an increase. Upon obtaining resistance in both strains, population studies were conducted to determine the characteristics of the resistance. Lt was found that a cessation of treatment for five generations did not significantly reduce resistance. The cross breeding of wild flies with resistant flies resulted in offspring that had a mortality curve closely matching the projected mortality curve of flies assumed to have resistance caused by a single dominant gene. There was no indication of resistance being sex linked. Finally, it was found that resistant flies are more susceptible t o malathion when they are reared at a higher temperature (30° C. instead of 25 ° C.).