Abstract
BackgroundVector-borne diseases are major public health concerns, and their control is threatened by the spread of insecticide resistance in vector populations. In this context, the use of repellents is an alternative approach to limit vector-host interactions. However, prior exposure to repellents is suspected to affect mosquito behavior at the subsequent exposure, possibly reducing the efficacy of the compound. Despite this, the effect of mosquito experience on repellent efficacy remains poorly documented. In the present study, we tested whether a first blood meal successfully obtained upon a DEET-treated net would affect the success at taking a second blood meal in spite of DEET in the malaria mosquito Anopheles gambiae (s.s.). The impact of DEET on mosquito life history traits after the first and the second exposure was also measured, in order to assess the long-term consequences of multiple exposures to DEET in vector insects.ResultsA first blood meal obtained upon a DEET-treated net did not influence the success of An. gambiae females to take a second blood meal in spite of DEET. However, data showed that a prior exposure to DEET negatively affected all life history traits tested in this study related to fecundity and fertility. DEET pre-exposed females displayed a reduction in blood engorgement at the second exposure, as well as a reduction in the number of eggs laid and in the proportion of offspring that reach adult stage. Also, an increase of mosquito activity was observed during the second blood meal in DEET-pre-exposed females. Taken together, these data suggest an overall impact of DEET exposure on mosquito fitness.ConclusionsOur results did not evidence any effect of a prior exposure to DEET on its efficacy during the second exposure. However, data show a negative impact of DEET exposure on mosquito fitness. These results give insights to understand the long-term efficacy of the most used mosquito repellent, and highlight that DEET induces deleterious effects on mosquito fitness in addition to repellency, potentially increasing its efficacy for controlling vector-borne diseases.
Highlights
Vector-borne diseases are major public health concerns, and their control is threatened by the spread of insecticide resistance in vector populations
We examined in An. gambiae (s.s.) the effects of a blood meal successfully obtained upon a DEET-treated net on the success of taking a second blood meal in spite of DEET presence using a biologically relevant time period between the two blood meals (i.e. 3–4 days)
Emanations of such impregnated net were measured in regards to sprayed DEET on skin according to the guidance for the use of DEET
Summary
Vector-borne diseases are major public health concerns, and their control is threatened by the spread of insecticide resistance in vector populations. The mixture restored a knockdown effect and mortality similar to pyrethroids against multi-loci resistant mosquitoes [13, 14] Such synergistic effect was observed, when used against pyrethroid-resistant mosquitoes, between repellents (both DEET and IR3535) and a pyrethroid insecticide impregnated with long-lasting polymer coating [15]. All together, these studies suggest that repellents may have important potential in vector control when impregnated singly or in mixtures on fabrics. The use of repellents appears to be a promising tool to target vector insects that are not reached by current insecticide-based methods, for instance conferring an outdoor protection [16]
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