Transcriptome Profiling and Genetic Study Reveal Amplified Carboxylesterase Genes Implicated in Temephos Resistance, in the Asian Tiger Mosquito Aedes albopictus

Abstract

BackgroundThe control of Aedes albopictus, a major vector for viral diseases, such as dengue fever and chikungunya, has been largely reliant on the use of the larvicide temephos for many decades. This insecticide remains a primary control tool for several countries and it is a potential reliable reserve, for emergency epidemics or new invasion cases, in regions such as Europe which have banned its use. Resistance to temephos has been detected in some regions, but the mechanism responsible for the trait has not been investigated.Principal findingsTemephos resistance was identified in an Aedes albopictus population isolated from Greece, and subsequently selected in the laboratory for a few generations. Biochemical assays suggested the association of elevated carboxylesterases (CCE), but not target site resistance (altered AChE), with this phenotype. Illumina transcriptomic analysis revealed the up-regulation of three transcripts encoding CCE genes in the temephos resistant strain. CCEae3a and CCEae6a showed the most striking up-regulation (27- and 12-folds respectively, compared to the reference susceptible strain); these genes have been previously shown to be involved in temephos resistance also in Ae. aegypti. Gene amplification was associated with elevated transcription levels of both CCEae6a and CCEae3a genes. Genetic crosses confirmed the genetic link between CCEae6a and CCEae3a amplification and temephos resistance, by demonstrating a strong association between survival to temephos exposure and gene copy numbers in the F2 generation. Other transcripts, encoding cytochrome P450s, UDP-glycosyltransferases (UGTs), cuticle and lipid biosynthesis proteins, were upregulated in resistant mosquitoes, indicating that the co-evolution of multiple mechanisms might contribute to resistance.SignificanceThe identification of specific genes associated with insecticide resistance in Ae. albopictus for the first time is an important pre-requirement for insecticide resistance management. The genomic resources that were produced will be useful to the community, to study relevant aspects of Ae. albopictus biology.

Genome sequence of the Asian Tiger mosquito,Aedes albopictus, reveals insights into its biology, genetics, and evolution

“…aegypti (35) and Ae. albopictus (36), is present in Ae. albopictus as two tandemly duplicated genes (AalBCCE013 and AalbCCE014).…”

Susceptibility profile and metabolic mechanisms involved in Aedes aegypti and Aedes albopictus resistant to DDT and deltamethrin in the Central African Republic

“…aegypti in Brazil [53] and Santiago Island in Cape Verde [54] and in Ae. albopictus in Greece [55]. Insecticide resistance results from extensive, long-term use [20, 21]; thus, for example, in Brazil, resistance to temephos compromises its use by the national dengue control programme [56, 57].…”

Whole genome sequencing reveals high complexity of copy number variation at insecticide resistance loci in malaria mosquitoes

“…quinquefasciatus resistance to permethrin is associated with increased expression of Cyp9m10, due in part to a duplication [22] Similarly, amplification of esterase genes leading to elevated expression provides increased resistance to organophosphates in the mosquitoes Cx. pipiens [23] and Aedes albopictus [24], and to several insecticides in the peach-potato aphid Myzus persicae [25,26]. In brown planthoppers, neofunctionalisation of a duplicated copy of Cyp6er1 has even created a novel gene variant providing resistance to the neonicotinoid imidacloprid [27].…”