Résumé
Understanding the dynamics of insecticide resistance genes in mosquito
populations is pivotal for a sustainable use of insecticides. Dieldrin
resistance in Aedes albopictus is conferred by the alanine to serine
substitution (A302S or RdlR allele) in the γ-aminobutyric acid (GABA)
receptor encoded by the Rdl gene. On Reunion Island, dieldrin resistance
was initially reported in natural Ae. albopictus populations sampled in
2008 despite the ban of dieldrin since 1994. To monitor insecticide
resistance in Ae. albopictus on the island and to identify its drivers, we
measured (i) the frequency of resistance alleles in 19 distinct natural
populations collected between 2016 and 2017, (ii) fitness costs associated
with dieldrin resistance in laboratory-controlled experiments, and (iii)
the resistance conferred by RdlR to fipronil, an insecticide widely used
on the island and reported to cross-react with RdlR. The results show a
persistence of RdlR in Ae. albopictus natural populations at low
frequencies. Among the measured life history traits, mortality in
pre-imaginal stages, adults’ survival as well as the proportion of
egg-laying females were significantly affected in resistant mosquitoes.
Finally, bioassays revealed resistance of RdlR mosquitoes to fipronil,
suggesting that the use of fipronil in natura could select for the RdlR
allele. This study shows that dieldrin resistance is persistent in natural
mosquito populations likely as a result of combined effects between
fitness costs associated with RdlR and selection exerted by cross-reacting
environmental insecticides such as fipronil.