Bioassay and molecular monitoring of insecticide resistance status in Aedes albopictus populations from Greece, to support evidence-based vector control

Background Aedes albopictushas a well-established presence in southern European countries, associated with recent disease outbreaks (e.g. chikungunya). Development of insecticide resistance in the vector is a major concern as its control mainly relies on the use of biocides. Data on the species' resistance status are essential for efficient and sustainable control. To date the insecticide resistance status ofAe. albopictuspopulations from Greece against major insecticides used in vector control remains largely unknown. Methods We investigated the insecticide resistance status of 19Ae. albopictuspopulations from 11 regions of Greece. Bioassays were performed against diflubenzuron (DFB),Bacillus thuringiensisvar.israelensis(Bti), deltamethrin and malathion. Known insecticide resistance loci were molecularly analysed, i.e. voltage-gated sodium channel (VGSC) mutations associated with pyrethroid resistance; presence and frequency of carboxylesterases 3 (CCEae3a) and 6 (CCEae6a) gene amplification associated with organophosphate (OP) resistance and; chitin synthase-1 (CHS-1) for the possible presence of DFB resistance mutations. Results Bioassays showed full susceptibility to DFB,Btiand deltamethrin, but resistance against the OP malathion (range of mortality: 55.30-91.40%).VGSCanalysis revealed a widespread distribution of the mutations F1534C (in all populations, with allelic frequencies between 6.6-68.3%), and I1532T (in 6 populations; allelic frequencies below 22.70%), but absence of V1016G.CCEgene amplifications were recorded in 8 out of 11 populations (overall frequency: 33%). Co-presence of the F1534C mutation andCCEae3aamplification was reported in 39 of the 156 samples analysed by both assays. No mutations at theCHS-1I1043 locus were detected. Conclusions The results indicate: (i) the suitability of larvicides DFB andBtiforAe. albopictuscontrol in Greece; (ii) possible incipient pyrethroid resistance due to the presence ofkdrmutations; and (iii) possible reduced efficacy of OPs, in a scenario of re-introducing them for vector control. The study highlights the need for systematic resistance monitoring for developing and implementing appropriate evidence-based control programmes.