Environmental Engineering Reference
In-Depth Information
Chapter 13
Exploring the Molecular Basis of Insecticide
S
é
bastien Marcombe, Rodolphe Poupardin, Frederic Darriet,
St
é
phane Reynaud, Julien Bonnet, Clare Strode, Cecile Brengues,
Andr
é
Y
é
bakima, Hilary Ranson, Vincent Corbel, and Jean-Philippe David
INTRODUCTION
The 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. Unfortu-
nately, vector control programs are facing operational challenges with mosquitoes be-
coming 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.
The present chapter 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 organophos-
phate 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 detoxifi cation enzymes inhibitors
prior to bioassays induced a signifi cant increased susceptibility of mosquitoes to insec-
ticides, revealing the presence of metabolic-based resistance mechanisms. This trend
was biochemically confi rmed by signifi cant 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 detoxifi cation and other insecticide resistance-related enzymes revealed
the signifi cant constitutive over-transcription of multiple detoxifi cation genes at both
larval and adult stages. The over-transcription of detoxifi cation genes in the resistant
strain was confi rmed by using real-time quantitative RT-PCR.
These 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 fi nding have important implications for dengue vector control in Martinique
and emphasizes the need to develop new tools and strategies for maintaining an effec-
tive control of
Aedes
mosquito populations worldwide.
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