Fitness Costs of Insecticide Resistance in Natural Breeding Sites of the Mosquito Culex Pipiens

Abstract

Genetic changes conferring adaptation to a new environment may induce a fitness cost in the previous environment. Although this prediction has been verified in laboratory conditions, few studies have tried to document this cost directly in natural populations. Here, we evaluated the pleiotropic effects of insecticide resistance on putative fitness components of the mosquito Culex pipiens. Experiments using different larval densities were performed during the summer in two natural breeding sites. Two loci that possess alleles conferring organophosphate (OP) resistance were considered: ace-1 coding for an acetylcholinesterase (AChE1, the OP target) and Ester, a ''super locus" including two closely linked loci coding for esterases A and B. Resistance ace-1 alleles coding for a modified AChE1 were associated with a longer development time and shorter wing length. The pleiotropic effects of two resistance alleles Ester1 and Ester4 coding for the overproduced esterases A1 and A4-B4, respectively, were more variable. Both A1 and A4-B4 reduced wing length, although only A1 was associated with a longer preimaginal stage. The fluctuating asymmetry (FA) of the wing did not respond to the presence or to the interaction of resistance alleles at the two loci at any of the density levels tested. Conversely, the FA of one wing section decreased when larval density increased. This may be the consequence of selection against less developmentally stable individuals. The results are discussed in relation to the local evolution of insecticide resistance genes.

Gene Dosage and Duplication

“…Another important aspect of insecticide resistance through gene duplication is that at least some of these duplications are actually deleterious in an environment without the pesticide (Raymond et al, 1998;Guillemaid et al, 1999;Bourguet et al, 2004;Foster et al, 2003Foster et al, , 2005. Thus, the impact of gene duplications on fitness can be dependent on the environmental conditions.…”

“…Duplications of genes can be beneficial under stressful conditions but deleterious in a benign environment (Brown et al, 1998;Raymond et al, 1998;Guillemaid et al, 1999;Kondrashov et al, 2002;Foster et al, 2003Foster et al, , 2005Bourguet et al, 2004;Francino, 2005;Lawrence, 2005); thus under stressful conditions the fitness function is closer to linear, or at least fast-growing diminishing returns, whereas in a normal setting the function is more of convex or optimum.…”

Fitness costs of resistance to Bti toxins in the dengue vector Aedes aegypti

“…The cost of insecticide resistance has been described both in selected laboratory strains and in field resistant populations (Bourguet et al 2004;Gassmann et al 2009). Resistance costs can be estimated in two major ways (Roux et al 2005a).…”

“…Resistance costs can be estimated in two major ways (Roux et al 2005a). The first one consists of directly comparing the life-history traits associated with fitness, such as survival, reproduction or behavior, of susceptible and resistant individuals (Bourguet et al 2004;Paris et al 2008;Gassmann et al 2009). In mosquitoes, resistances to chemical insecticides were shown to increase development time or to reduce survival, fecundity, wing length or mating success (De Oliveira et al 2003;Bourguet et al 2004;Berticat et al 2008).…”

Cloning and characterization of ribosomal protein S29, a deltamethrin resistance associated gene from Culex pipiens pallens

“…For example, it has been reported that emergence percentage of the susceptible strain was significantly greater than that of the Kdr-resistant strains in an insecticide-free environment (Berticat et al 2008). AChE1-resistant strains were associated with a longer development time and shorter wing length (Bourguet et al 2004).…”