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 degrees 41' latitude in Florida to 44 degrees 2' in Maine) in which the percentage of standard XY(M) males increased with increasing latitude. In Florida, 100% of the males possessed the M factor on the third autosome (III(M)). North Carolina had 20% III(M) males and 2.35% with both Y(M) and III(M). Fewer III(M) 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 A(M)): CS (III(M)) and SRS (V(M)). 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% III(M) 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.

House flies were collected from four dairies in Maine, New York, North Carolina, and Florida, where high levels of resistance to permethrin have been documented. Regions of two genes, CYP6D1 and Vssc1, having alleles that confer resistance to permethrin (and other pyrethroids) were analysed from individuals at each collection site. The combinations of resistance alleles for Vssc1 and CYP6D1 were highly variable between each state. The resistance allele CYP6D1v1 was found at a high frequency (0.63-0.91) at all sites. Individuals homozygous susceptible for CYP6D1 were very rare and detected only at the dairy in Maine. In addition to the typical Vssc1 mutation responsible for resistance, kdr (L1014F), we also identified individuals with a L1014H mutation. Although house flies homozygous for the L1014H mutation had a lower level of resistance to permethrin, compared to L1014F, the H1014 resistance allele was frequently detected. No individuals with the super-kdr allele (M918T + L1014F) were detected from the field collections. The intron 3 bp downstream of the kdr mutation was found to be extremely variable, providing an opportunity to reconstruct a phylogeny of Vssc1 alleles. Based on this analysis it appears the kdr-his mutation had multiple evolutionary origins, but that the kdr mutation may have had a single origin. The impacts of these findings on resistance management are discussed.

Sex determination is one of the most rapidly evolving developmental pathways, but the factors responsible for this fast evolution are not well resolved. The house fly, Musca domestica, is an ideal model for studying sex determination because house fly sex determination is polygenic and varies considerably between populations. Male house flies possess a male-determining locus, the M factor, which can be located on the Y or X chromosome or any of the five autosomes. There can be a single M or multiple M factors present in an individual male, in heterozygous or homozygous condition. Males with multiple copies of M skew the sex ratio toward the production of males. Potentially in response to these male-biased sex ratios, an allele of the gene transformer, Md-traD, promotes female development in the presence of one or multiple M factors. There have been many studies to determine the linkage and frequency of these male determining factors and the frequency of Md-traD chromosomes in populations from around the world. This review provides a summary of the information available to date regarding the patterns of distribution of autosomal, X-linked and Y-linked M factors, the relative frequencies of the linkage of M, the changes in frequencies found in field populations, and the fitness of males with autosomal M factors vs. Y-linked M. We evaluate this natural variation in the house fly sex determination pathway in light of models of the evolution of sex determination.

The lesser mealworm, Alphitobius diaperinus (Panzer), is an important pest in poultry facilities. The toxicity of cyfluthrin and tetrachlorvinphos to five strains of the lesser mealworm was compared with the toxicity to a susceptible laboratory strain. Bioassays were carried out with both larvae and adults. For the susceptible strain, cyfluthrin and tetrachlorvinphos had similar toxicity to adults, but cyfluthrin was 5 times more toxic to larvae when compared with tetrachlorvinphos. High levels of resistance to tetrachlorvinphos in two beetle strains were detected in both larvae and adults, although these strains were heterogeneous and still contained susceptible individuals. Resistance to cyfluthrin ranged from 1.7- to 9.5-fold for adults and from 0.5- to 29-fold for larvae at the LC(95). Overall, the patterns of resistance did not mirror the insecticide use patterns reported at these facilities. The implications of these results to management of the lesser mealworms are discussed.

2016-11-03T14:11:40

In the house fly, Musca domestica L. (Diptera: Muscidae), sex is usually determined by a dominant factor, M, located on the Y chromosome. However, there are autosomal male (A(M)) populations in which the M factor is located on one or more of the five autosomes (I-V), most commonly on the third chromosome. Herein we report the use of isogenic strains to determine the relative fitness of Y(M) versus III(M) males in three different experiments. First, cages were started with 50% Y(M) and 50% III(M) males, and the frequencies of Y(M) and III(M) males were evaluated across generations. Second, mating competition studies were preformed with these isogenic strains. Third, the relative emergence rates of III(M) versus Y(M) male pupae held at three temperatures for 3 d were examined. All three studies indicate that III(M) males have a greater fitness than Y(M) males. In the cage competition studies, >90% of the males were III(M) after seven generations. III(M) males were more likely to mate than Y(M) males, and a higher percent of III(M) males emerged after being held as pupae at 4, 16, or 28 degrees C for 3 d. The implications of these studies to the distribution of III(M) and Y(M) males in field populations are discussed.

No abstract

In the housefly, Musca domestica L., sex is usually determined by a dominant factor, M, located on the Y chromosome. However, there are 'autosomal male' (AM) populations in which the M factor is located on one or more of the five autosomes (I-V) or on X. We examined changes in the frequency of AM and YM males in North Carolina populations of houseflies after 4 years in the laboratory (NC Lab 02:06) and after 4 or 5 years in the field (NC 2006 and NC 2007). In 2002, 77.7% of the male houseflies were III/III;XYM, 20% were IIIM/III;XX, and 2.3% were IIIM/III;XYM. After 4 years in the laboratory, IIIM/III males disappeared and 17.4% of the males were XMYM. Conversely, 4 years later, the field population was relatively unchanged from 2002. Thus, there was a strong selection against IIIM/III males in the laboratory, but not in the field. Field-collected flies from 2007 indicated a slight increase in the frequency of XYM males and a slight decrease in the frequency of IIIM/III males (relative to 2002 and 2006), suggesting that the relative frequency of XYM and IIIM/III can vary slightly over time in field populations. The detection of XMYM males in 2007 offered the opportunity to evaluate the frequency of the female-determining FD factor, which was found to be present in both the laboratory and field populations, but frequencies varied greatly. The present study represents the first report of FD in houseflies from North America. The significance of these results, relative to observed clines in AM versus YM males, is discussed.