Abstract
BackgroundThe yellow fever mosquito Aedes aegypti is a major vector of dengue and hemorrhagic fevers, causing up to 100 million dengue infections every year. As there is still no medicine and efficient vaccine available, vector control largely based on insecticide treatments remains the only method to reduce dengue virus transmission. Unfortunately, vector control programs are facing operational challenges with mosquitoes becoming resistant to commonly used insecticides. Resistance of Ae. aegypti to chemical insecticides has been reported worldwide and the underlying molecular mechanisms, including the identification of enzymes involved in insecticide detoxification are not completely understood.ResultsThe present paper investigates the molecular basis of insecticide resistance in a population of Ae. aegypti collected in Martinique (French West Indies). Bioassays with insecticides on adults and larvae revealed high levels of resistance to organophosphate and pyrethroid insecticides. Molecular screening for common insecticide target-site mutations showed a high frequency (71%) of the sodium channel 'knock down resistance' (kdr) mutation. Exposing mosquitoes to detoxification enzymes inhibitors prior to bioassays induced a significant increased susceptibility of mosquitoes to insecticides, revealing the presence of metabolic-based resistance mechanisms. This trend was biochemically confirmed by significant elevated activities of cytochrome P450 monooxygenases, glutathione S-transferases and carboxylesterases at both larval and adult stages. Utilization of the microarray Aedes Detox Chip containing probes for all members of detoxification and other insecticide resistance-related enzymes revealed the significant constitutive over-transcription of multiple detoxification genes at both larval and adult stages. The over-transcription of detoxification genes in the resistant strain was confirmed by using real-time quantitative RT-PCR.ConclusionThese results suggest that the high level of insecticide resistance found in Ae. aegypti mosquitoes from Martinique island is the consequence of both target-site and metabolic based resistance mechanisms. Insecticide resistance levels and associated mechanisms are discussed in relation with the environmental context of Martinique Island. These finding have important implications for dengue vector control in Martinique and emphasizes the need to develop new tools and strategies for maintaining an effective control of Aedes mosquito populations worldwide.
Highlights
The yellow fever mosquito Aedes aegypti is a major vector of dengue and hemorrhagic fevers, causing up to 100 million dengue infections every year
This mechanism may result from two distinct but additive genetic events: i) a mutation of the enzyme protein sequence leading to a better metabolism of the insecticide, and/or ii) a mutation in a non-coding regulatory region leading to the over-production of an enzyme capable of metabolizing the insecticide
The level of resistance to temephos of the Vauclin strain was significantly reduced in the presence of piperonyl butoxide (PBO), DEF and DMC indicating the involvement of P450 monooxygenases (P450s), CCEs and in a lesser extent glutathione S-transferases (GSTs) in the resistance of larvae to temephos
Summary
The yellow fever mosquito Aedes aegypti is a major vector of dengue and hemorrhagic fevers, causing up to 100 million dengue infections every year. Most of dengue vector control programs implemented worldwide are facing operational challenges with the emergence and development of insecticide resistance in Ae. aegypti [2] and Ae. albopictus [3]. Metabolic-based resistance involves the bio-transformation of the insecticide molecule by enzymes and is considered as a key resistance mechanism of insects to chemical insecticides [8,9]. The rapid expansion and diversification of these socalled 'detoxification enzymes' in insects is likely to be the consequence of their adaptation to a broad range of natural xenobiotics found in their environment such as plant toxins [13] These enzymes have been involved in mosquito response to various anthropogenic xenobiotics such as heavy metals, organic pollutants and chemical insecticides [14,15,16]
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