Insecticide resistance genes induce a mating competition cost in Culex pipiens mosquitoes

Abstract

Resistance to organophosphorus insecticides (OP) in Culex pipiens mosquitoes represents a convenient model for investigating the fitness cost of resistance genes and its origin, since both the environmental changes in nature and the adaptive genes are clearly identified. Two loci are involved in this resistance--the super-locus Ester and the locus Ace.1--each displaying several resistance alleles. Population surveys have shown differences in fitness cost between these resistance genes and even between resistance alleles of the same locus. In order to better understand this fitness cost and its variability, the effects of these resistance genes on several fitness-related traits are being studied. Here, through competition experiments between two males for the access to one female, we analysed the effect on paternity success associated with three resistance alleles--Ester4, Ester1 and Ace.1R--relative to susceptible males and relative to one another. The eventual effect of female genotype on male mating success was also studied by using susceptible and resistant females. The strains used in this experiment had the same genetic background. Susceptible males had a mating advantage when competing with any of the resistant males, suggesting a substantial cost of resistance genes to this trait. When competing against susceptible males, the paternity success did not vary among resistant males, whatever the genotype of the female. When competing against other resistant males, no difference in paternity success was apparent, except when the female was Ester1.

Seasonal fluctuation in susceptibility to insecticides within natural populations of Drosophila melanogaster. II. Features of genetic variation in susceptibility to organophosphate insecticides within natural populations of D. melanogaster

“…Until now, reversion to susceptibility has often been observed in laboratory or field populations of insects, and fitness costs or deleterious effects of resistance genes have been observed (mosquito Culex pipiens: Berticat et al, 2002;Berticat et al, 2004;Bourguet et al, 2004 : Foster et al, 2003;Foster et al, 2005). If resistance factors have disadvantageous effects on fitness, it is expected that the frequencies of resistance factors within insect populations tend to decrease under no insecticide environments, which results in the tendency towards a decrease in levels of resistance to insecticides within insect populations (Crow, 1957).…”

Fitness evaluation of two Brazilian Aedes aegypti field populations with distinct levels of resistance to the organophosphate temephos

“…Mating efficiency was inversely proportional to the temephos resistance ratio. Using a different approach, Berticat et al (2002) demonstrated that OP resistance significantly affects the insemination rate of Cx. pipiens, resistant males being less competitive.…”

“…Several parameters of insect biology can be affected by pesticide resistance, such as development time, adult longevity, behaviour, reproduction and the immune system (Berticat et al 2002, Rivero et al 2010. Once altered, these aspects have the potential to influence both the dynamics of insecticide resistance dissemination and the relationship among vectors and the parasites they transmit.…”

Insecticide resistance genes confer a predation cost on mosquitoes, Culex pipiens

“…Four strains sharing the same genetic background and only differing by their genotype at Ester and/or ace-1 locus were used: the insecticide-susceptible strain S-LAB, homozygous for ace-1 S and Ester 0 (Georghiou et al, 1966) ; the resistant strains SA1 and SA4, homozygous for ace-1 S and for the resistance alleles Ester 1 and Ester 4 , respectively ; and finally, the resistant strain SR, homozygous for Ester 0 and for the resistance allele ace-1 R (Berticat et al, 2002 a). Before all experiments, all strains were reared under the same standardized conditions for a minimum of 5 generations, preventing possible maternal effects.…”