Geometric Morphometrics of Nine Field Isolates of Aedes aegypti with Different Resistance Levels to Lambda-Cyhalothrin and Relative Fitness of One Artificially Selected for Resistance

Abstract

Aedes aegypti, a mosquito closely associated with humans, is the principal vector of dengue virus which currently infects about 400 million people worldwide. Because there is no way to prevent infection, public health policies focus on vector control; but insecticide-resistance threatens them. However, most insecticide-resistant mosquito populations exhibit fitness costs in absence of insecticides, although these costs vary. Research on components of fitness that vary with insecticide-resistance can help to develop policies for effective integrated management and control. We investigated the relationships in wing size, wing shape, and natural resistance levels to lambda-cyhalothrin of nine field isolates. Also we chose one of these isolates to select in lab for resistance to the insecticide. The main life-traits parameters were assessed to investigate the possible fitness cost and its association with wing size and shape. We found that wing shape, more than wing size, was strongly correlated with resistance levels to lambda-cyhalothrin in field isolates, but founder effects of culture in the laboratory seem to change wing shape (and also wing size) more easily than artificial selection for resistance to that insecticide. Moreover, significant fitness costs were observed in response to insecticide-resistance as proved by the diminished fecundity and survival of females in the selected line and the reversion to susceptibility in 20 generations of the non-selected line. As a practical consequence, we think, mosquito control programs could benefit from this knowledge in implementing efficient strategies to prevent the evolution of resistance. In particular, the knowledge of reversion to susceptibility is important because it can help in planning better strategies of insecticide use to keep useful the few insecticide-molecules currently available.

Insecticide resistance, associated mechanisms and fitness aspects in two Brazilian Stegomyia aegypti (= Aedes aegypti) populations

“…The amount of blood ingested is critical to mosquito vector capacity because it directly influences the quantity of ingested parasites and the number of eggs laid (Belinato et al ., , ; Belinato & Valle, ). Despite its relevance, this parameter is generally neglected when fitness evaluations are concerned (Jaramillo‐O et al ., ; Diniz et al ., ). The present data indicate a decreased ability of Aracaju females to ingest blood in comparison with the control Rockefeller strain.…”

“…In the absence of known insecticide-susceptible Brazilian field populations, and taking into account the need for a control to compare fitness evaluations, the Rockefeller strain, a reference strain of both insecticide susceptibility and vigour, was employed, as it has been previously (Belinato et al, 2012;Martins et al, 2012;Brito et al, 2013;Jaramillo-O et al, 2014;. Although Rockefeller is undoubtedly more adapted to laboratory conditions, in the case of S. aegypti it is necessary to employ a laboratory strain in order to compare fitness performances of populations that are resistant or susceptible to insecticides.…”

“…In these cases, although resistant insects are more likely to survive in the face of exposure to the insecticide, in its absence resistant specimens tend to be less competitive (Brito et al, 2013). Indeed, there are several registers of adaptive costs associated with insecticide resistance in disease vector mosquitoes (Berticat et al, 2002;Rivero et al, 2010;Belinato et al, 2012;Jaramillo-O et al, 2014;Diniz et al, 2015).…”

Assessing the effect of selection with deltamethrin on biological parameters and detoxifying enzymes in Aedes aegypti (L.)

“…These was assessed before regarding the selection forward and reverse for 20 generations with lambda‐cyhalothrin in a strain of Ae. aegypti …”

“…Fecundity although shown to be different between selected lines (F 9 and F 10 ) from the susceptible Rockefeller strain, there were no differences between the selected and non‐selected lines. Life table parameters like net reproductive rate per generation ( R o ) and the intrinsic rate of increase in days ( r m ) showed significant differences between the non‐selected and selected lines; besides the r m parameter did not show differences with the Rockefeller strain . In two populations of Ae.…”