Assessing the Effects of Aedes aegypti kdr Mutations on Pyrethroid Resistance and Its Fitness Cost

Abstract

Pyrethroids are the most used insecticide class worldwide. They target the voltage gated sodium channel (NaV), inducing the knockdown effect. In Aedes aegypti, the main dengue vector, the AaNaV substitutions Val1016Ile and Phe1534Cys are the most important knockdown resistance (kdr) mutations. We evaluated the fitness cost of these kdr mutations related to distinct aspects of development and reproduction, in the absence of any other major resistance mechanism. To accomplish this, we initially set up 68 crosses with mosquitoes from a natural population. Allele-specific PCR revealed that one couple, the one originating the CIT-32 strain, had both parents homozygous for both kdr mutations. However, this pyrethroid resistant strain also presented high levels of detoxifying enzymes, which synergistically account for resistance, as revealed by biological and biochemical assays. Therefore, we carried out backcrosses between CIT-32 and Rockefeller (an insecticide susceptible strain) for eight generations in order to bring the kdr mutation into a susceptible genetic background. This new strain, named Rock-kdr, was highly resistant to pyrethroid and presented reduced alteration of detoxifying activity. Fitness of the Rock-kdr was then evaluated in comparison with Rockefeller. In this strain, larval development took longer, adults had an increased locomotor activity, fewer females laid eggs, and produced a lower number of eggs. Under an inter-strain competition scenario, the Rock-kdr larvae developed even slower. Moreover, when Rockefeller and Rock-kdr were reared together in population cage experiments during 15 generations in absence of insecticide, the mutant allele decreased in frequency. These results strongly suggest that the Ae. aegypti kdr mutations have a high fitness cost. Therefore, enhanced surveillance for resistance should be priority in localities where the kdr mutation is found before new adaptive alleles can be selected for diminishing the kdr deleterious effects.

Fitness costs of key point mutations that underlie acaricide target‐site resistance in the two‐spotted spider miteTetranychus urticae

“…In contrast, using near‐isogenic lines, the kdr and/or super‐kdr mutations in VGSCs of various insect species have previously been shown to induce changes in life‐history parameters [for instance oviposition in A. aegypti (Brito et al., 2013) and survival to adulthood in C. quinquefasciatus (Berticat et al., 2008)]. Moreover, these mutations also appear to affect nerve functioning and behavior in insect species.…”

“…Moreover, these mutations also appear to affect nerve functioning and behavior in insect species. For example, a pyrethroid‐resistant strain of Musca domestica responds differently to changes in temperature (Foster et al., 2003) and pyrethroid resistance in A. gambiae and A. aegypti is associated with a lowered ability of host seeking and an increased locomotor activity, respectively (Brito et al., 2013; Diop et al., 2015). It is therefore possible that we have missed a potential pleiotropic effect of the L1024V mutation on the behavior of T. urticae .…”

“…Excluding a number of studies that have focused on mosquitoes [ Culex pipiens quinquefasciatus (Berticat, Boquien, Raymond, & Chevillon, 2002; Berticat et al., 2008; Gazave, Chevillon, Lenormand, Marquine, & Raymond, 2001), Aedes aegypti (Brito et al., 2013), and Anopheles gambiae (Diop et al., 2015)], the Australian blow fly L. cuprina (McKenzie, 1990, 1994), and the peach aphid Myzus persicae (Foster, Denholm, & Devonshire, 2000), the majority of previous work that assesses pesticide resistance‐related fitness costs in arthropods suffers from multiple design weaknesses [see also reviews by ffrench‐Constant and Bass (2017) and Kliot and Ghanim (2012)]. A common design flaw is the evaluation of genetically unrelated populations in the experimental setup.…”

“…An elegant solution to overcome this experimental limitation is to backcross the target‐site mutation of interest into a susceptible genomic background over multiple generations, hereby generating near‐isogenic lines. This procedure maximizes the chance that the observed difference in population growth is caused by the target‐site mutation under investigation (Bajda et al., 2017; Brito et al., 2013; Riga et al., 2017). Unfortunately, the biological characteristics of many insect and mite pests render the generation of near‐isogenic lines extremely difficult and time‐consuming.…”

Identifying genomic changes associated with insecticide resistance in the dengue mosquito Aedes aegypti by deep targeted sequencing

“…Indeed, recombination events are probably countering such association, especially as the VGSC gene and amplified detoxification genes are located on distant genomic regions. In addition, fitness costs associated with both kdr mutations and gene amplifications have been identified (Kondrashov 2012;Brito et al 2013;Katju and Bergthorsson 2013;Rinkevich et al 2013 …”