Abstract
Two unique housefly strains, MSS and N-MRS, were selected and used to clarify mechanisms of sex-associated malathion resistance in the housefly, Musca domestica. Compared with the lab-susceptible CSS strain, susceptible females and resistant males were observed in the malathion-susceptible MSS strain, while the malathion-resistant near-isogenic line, N-MRS, achieved similar resistance level between genders. Significant synergistic effect of the esterase-inhibitor DEF on resistant houseflies pointed to the important involvement of esterase in this specific malathion resistance. Examination of the carboxylesterase gene MdαE7 in malathion resistant housefly populations found seven, non-synonymous SNP mutations (Ser250-Thr, Trp251-Ser, Met303-Ile, Leu354-Phe, Ser357-Leu, Trp378-Arg and Ser383-Thr), not found in susceptible houseflies, revealing a strong correlation between these mutations and the development of malathion resistance. Further genetic analysis conducted with bioassays by topical application and nucleotide polymorphism detection provided a first line of molecular evidence for a linkage between a male-determining factor and MdαE7 gene in the MSS and N-MRS males. This linkage results in a much higher level of malathion resistance for males than females in the MSS strain. Lastly, quantitative real-time PCR showed that MdαE7 was over expressed in the resistant strain due to the increased transcription level of mRNA rather than gene duplication.
Highlights
The housefly, Musca domestica L. is a serious threat to human and animal health by carrying more than 100 pathogens[1]
Given that the carboxylesterase gene MdαE7 was suggested to be responsible for malathion resistance of houseflies[2,17], in this manuscript we report the establishment of a Near-isogenic lines (NILs) of malathion-resistant (N-MRS) housefly to minimize the differences in genetic backgrounds, theoretically enabling clarification of the involvement of multiple mutations and MdαE7 overexpression in sex-specific malathion resistance
The synergistic ratios for the MSS males, N-MRS females, and N-MRS males pretreated with DEF were 176, 294, and 127, respectively, while the corresponding value for the MSS females was 1.86
Summary
The housefly, Musca domestica L. is a serious threat to human and animal health by carrying more than 100 pathogens[1]. In several dipteran and hemipteran insects, it is generally accepted that OP resistance is mainly mediated by enhanced metabolic detoxification or sequestration through quantitative changes in activity of general esterases[5] Quantitative changes, such as gene duplication or up-regulation, or a combination of both, lead to the overproduction of enzymes[6]. The same mutation Gly137Asp in both genes was proposed to be responsible for diazinon resistance, while another substitution Trp251Leu in LcαE7 and Trp251Ser in MdαE7 was involved in malathion resistance[2,16,17] Since these seminal studies, mutation of esterase genes mediating OP resistance has been identified in many insect species[18]. Several insect NILs have been utilized for genetic analyses of insecticide resistance[28,29,30,31], resistance gene mapping and cloning[32], and fitness tests[33]
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