A cline in frequency of autosomal males is not associated with insecticide resistance in house fly (Diptera: Muscidae)

Abstract

Geographic variation in the chromosomal location of the male sex determining factor (M) was studied in four house fly, Musca domestica L., populations from the eastern United States. We found a strong clinal trend (29° 41′ latitude in Florida to 44° 2′ in Maine) in which the percentage of standard XYM males increased with increasing latitude. In Florida, 100% of the males possessed the M factor on the third autosome (IIIM). North Carolina had 20% IIIM males and 2.35% with both YM and IIIM. Fewer IIIM males were found in New York (4.35%). Populations from Maine contained 100% XY M males. In two of three standard laboratory-susceptible strains, all males carried M on an autosome ("autosomal males" or AM): CS (IIIM) and SRS (VM). Insecticide bioassays of four field-collected strains led us to conclude that resistance is not correlated with sex determination over a broad range of insecticides. For example, high levels of resistance to permethrin (86-99% survival at a diagnostic concentration) were found in all four field-collected strains. The five other insecticides evaluated showed varying levels of resistance among field strains. We conclude that a cline is present in house fly populations from the eastern United States with 100% IIIM males in the south and entirely Y M males in the north and that insecticide resistance is not a key factor influencing the evolution or linkage of M. © 2005 Entomological Society of America.