Volume 56, Issue 4
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



The genetic mechanisms that confer larval permethrin resistance were investigated in two strains of , vectors of yellow fever and dengue hemorrhagic fever. Larval resistance to permethrin in an field-collected resistant Couva () strain was associated with the sex-determining locus by analysis of back-crosses to the susceptible Rockefeller () strain. The median lethal concentrations (LCs) of these strains were 23.1 (95% confidence interval = 22.0–24.3) and 2.2 (2.0–2.3) parts/billion of permethrin, respectively. The estimated resistance ratio (RR) for the strain was 10.8 (10.3–11.4) compared with the strain. Resistance was inherited as partly recessive (dominance [D] = - 0.31) with an estimated RR of 2.3 (2.1–2.4) in the F hybrids when the parent was male. There were also significantly male-biased sex ratios for this cross. In contrast, inheritance was slightly dominant (D = 0.19) with an estimated RR of 4.1 (3.8–4.4) when the parent was female, and no significant sex ratio bias of progeny was observed. Analysis revealed a strong paternal-strain effect in bioassay mortality, sex ratio, egg hatch, and fecundity. A maternal-strain effect was also evident for bioassay mortality. Similarly, a strong maternal by paternal strain interaction was also evident for sex ratio. Progeny of single-family backcrosses of F hybrids to were statistically homogeneous for sex ratio, duration of oviposition, fecundity, and hatch rate. A significant increase in male bias was found for only one backcross to , after treatment with permethrin. In contrast, complex patterns of inheritance of life histories were observed among backcrosses to Backcrosses to had greater mean fecundities, shorter mean times to the start of oviposition, and shorter mean oviposition periods than did backcrosses to Hatch rates were statistically homogeneous among backcrosses, but all strikingly reduced relative to the parental generation. Times of start and duration of oviposition were highly negatively correlated with fecundity (first gonotropic cycle only) and rate of egg hatch. Females with lower fecundities had lower hatch rates, and there was a threshold of approximately 80 eggs per female, below which no eggs hatched. Generally all backcrosses had higher LCs than expected from single-locus inheritance. Association between sex bias and inheritance of resistance was apparent, but no single genetic linkage model based on current understanding of sex chromosome genetics was consistent with these observations. These results may have epidemiologic importance considering that permethrin-soaked bed nets are being used in many countries to control the biting activity of disease vectors.


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