Spatio-Temporal Dynamics of a Dieldrin Resistance Gene in Aedes albopictus and Culex quinquefasciatus Populations From Reunion Island

Abstract

The control of mosquito populations using insecticides is increasingly threatened by the spread of resistance mechanisms. Dieldrin resistance, conferred by point mutations in the Rdl gene encoding the γ-aminobutyric acid receptor, has been reported at high prevalence in mosquito populations in response to selective pressures. In this study, we monitored spatio-temporal dynamics of the resistance-conferring RdlR allele in Aedes (Stegomyia) albopictus (Skuse, 1895) and Culex (Culex) quinquefasciatus (Say, 1823) populations from Reunion Island. Specimens of both mosquito species were sampled over a 12-month period in three cities and in sites located at lower (<61 m) and higher (between 503 and 564 m) altitudes. Mosquitoes were genotyped using a molecular test detecting the alanine to serine substitution (A302S) in the Rdl gene. Overall, the RdlR frequencies were higher in Cx. quinquefasciatus than Ae. albopictus. For both mosquito species, the RdlR frequencies were significantly influenced by location and altitude with higher RdlR frequencies in the most urbanized areas and at lower altitudes. This study highlights environmental factors that influence the dynamics of insecticide resistance genes, which is critical for the management of insecticide resistance and the implementation of alternative and efficient vector control strategies.

Keywords: dieldrin; dynamics; insecticide; mosquito; resistance.

Graphical abstract

Fig. 1.

Map of Reunion Island showing the cities and sites where Aedes albopictus and Culex quinquefasciatus mosquitoes were collected. This map was modified from the CIRAD AWARE data (https://aware.cirad.fr/layers/geonode:classif_2018_s67_final_code1_com). According to the land use report of Bertrand Ballet of the Ministry of agriculture (https://agreste.agriculture.gouv.fr/agreste-web/download/publication/publie/Dos2103/Dossiers%202021-3_TERUTI.pdf) there was no significant change in the size of agricultural, urbanized, forest and natural areas between 2012 and 2018 on Reunion Island. Therefore, data from 2018 reflects the situation prevailing in 2012 when sampling was carried out. Dark gray corresponds to forest and natural area, light gray to agricultural area and black to urbanized area. In each city, both mosquito species were collected in two sites; the first one at a low altitude (< 61 m) and the other one at a higher altitude (i.e. between 503 m and 564 m).

Fig. 2.

Dynamics of the resistant Rdl^R (A302S) allele frequencies in field populations of Aedes albopictus and Culex quinquefasciatus. Mosquitoes of both species were sampled monthly as larvae in breeding sites set up in three cities (Saint-Benoît, Saint-Denis and Saint-Paul) of Reunion Island. In each city, two sites were selected: the first one at a low altitude (< 61 m) and the second one at a high altitude (between 503 and 564 m). Dots represent the resistant allele frequencies, and the line represent the less smoother line with the associated 95% confidence indicated in grey.