title: Contrasting patterns of tolerance between chemical and biological insecticides in mosquitoes exposed to UV-A.
abstract: Mosquitoes are vectors of major human diseases, such as malaria, dengue or yellow fever. Because no efficient treatments or vaccines are available for most of these diseases, control measures rely mainly on reducing mosquito populations by the use of insecticides. Numerous biotic and abiotic factors are known to modulate the efficacy of insecticides used in mosquito control. Mosquito breeding sites vary from opened to high vegetation covered areas leading to a large ultraviolet gradient exposure. This ecological feature may affect the general physiology of the insect, including the resistance status against insecticides. In the context of their contrasted breeding sites, we assessed the impact of low-energetic ultraviolet exposure on mosquito sensitivity to biological and chemical insecticides. We show that several mosquito detoxification enzyme activities (cytochrome P450, glutathione S-transferases, esterases) were increased upon low-energy UV-A exposure. Additionally, five specific genes encoding detoxification enzymes (CYP6BB2, CYP6Z7, CYP6Z8, GSTD4, and GSTE2) previously shown to be involved in resistance to chemical insecticides were found over-transcribed in UV-A exposed mosquitoes, revealed by RT-qPCR experiments. More importantly, toxicological bioassays revealed that UV-exposed mosquitoes were more tolerant to four main chemical insecticide classes (DDT, imidacloprid, permethrin, temephos), whereas the bioinsecticide Bacillus thuringiensis subsp. israelensis (Bti) appeared more toxic. The present article provides the first experimental evidence of the capacity of low-energy UV-A to increase mosquito tolerance to major chemical insecticides. This is also the first time that a metabolic resistance to chemical insecticides is linked to a higher susceptibility to a bioinsecticide. These results support the use of Bti as an efficient alternative to chemical insecticides when a metabolic resistance to chemicals has been developed by mosquitoes.
authors.affiliation: Laboratoire d'Ecologie Alpine, LECA-UMR 5553, Université de Grenoble 1, BP 53, 38041 Grenoble cedex 09, France. guillaume.tetreau@gmail.com
authors.forename: Guillaume
authors.initials: G
authors.lastname: Tetreau
authors.forename: Alexia
authors.initials: A
authors.lastname: Chandor-Proust
authors.forename: Frédéric
authors.initials: F
authors.lastname: Faucon
authors.forename: Renaud
authors.initials: R
authors.lastname: Stalinski
authors.forename: Idir
authors.initials: I
authors.lastname: Akhouayri
authors.forename: Sophie M
authors.initials: SM
authors.lastname: Prud'homme
authors.forename: Muriel
authors.initials: M
authors.lastname: Raveton
authors.forename: Stéphane
authors.initials: S
authors.lastname: Reynaud
mesh_terms: D000818:Animals; D009033:Culicidae / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000528:radiation effects*; D003580:Cytochromes / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation / Q000528:radiation effects; D005786:Gene Expression Regulation / Q000528:radiation effects; D007305:Insecticide Resistance / Q000528:radiation effects*; D007306:Insecticides / Q000633:toxicity*; D007814:Larva / Q000201:enzymology / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D003580:Cytochromes; D007306:Insecticides
keywords: Aedes aegypti; Bioassays; Candidate gene expression; Enzymatic activities; RT-qPCR; Ultraviolet