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

Abstract

Background: Aedes albopictus has 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 of Ae. albopictus populations from Greece against major insecticides used in vector control remains largely unknown. Methods: We investigated the insecticide resistance status of 19 Ae. albopictus populations from 11 regions of Greece. Bioassays were performed against diflubenzuron (DFB), Bacillus thuringiensis var. 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, Bti and deltamethrin, but resistance against the OP malathion (range of mortality: 55.30-91.40%). VGSC analysis 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. CCE gene amplifications were recorded in 8 out of 11 populations (overall frequency: 33%). Co-presence of the F1534C mutation and CCEae3a amplification was reported in 39 of the 156 samples analysed by both assays. No mutations at the CHS-1 I1043 locus were detected. Conclusions: The results indicate: (i) the suitability of larvicides DFB and Bti for Ae. albopictus control in Greece; (ii) possible incipient pyrethroid resistance due to the presence of kdr mutations; and (iii) possible reduced efficacy of OPs, in a scenario of reintroducing them for vector control. The study highlights the need for systematic resistance monitoring for developing and implementing appropriate evidence-based control programmes.

Bacterial Toxins Active against Mosquitoes: Mode of Action and Resistance

“…The assessment of the Bti susceptibility of non-treated populations has shown a range of natural variations before the introduction of this microbial larvicide ( Table 2 ). Variations in the resistance ratios (RR) ranged from 0.8- to 8-fold for Aedes species [ 231 , 232 , 234 , 320 , 321 , 322 , 323 , 324 , 325 , 326 , 327 , 328 ], from 1.5 to 12.5-fold for Cx. p. pipiens [ 234 , 329 , 330 ], and from 0.8- to 5.9-fold for Anopheles [ 234 , 303 , 331 ].…”

Effects of Selection to Diflubenzuron and Bacillus thuringiensis Var. Israelensis on the Overwintering Successes of Aedes albopictus (Diptera: Culicidae)

“…In support of our findings, a recent survey revealed 100% mortality of Ae. albopictus populations collected from different regions of Greece at DFB doses below 0.02 mg/L, suggesting also high susceptibility [22]. On the other hand, the estimated LC 50 value for Bti was 4.8 to 7.5-fold lower compared to the respective values recorded for other Greek populations of this species according to the previously mentioned study.…”

“…While a recent study suggests their suitability for the effectiveness control of Ae. albopictus [22], findings regarding other species do not fully confirm this point of view. In particular, high levels (up to 128-fold) of DFB resistance associated with specific mutations in the Chitin synthase gene have been identified in wild Cx.…”

“…albopictus as in our case, are capable of developing appreciable resistance levels. Recent evidences suggest the high suitability of DFB for the Asian tiger mosquito control [22], and this is partially true for other medically important mosquito species. In particular, very high DFB resistance levels have already been detected in wild populations of Cx.…”

“…Upon adult emergence, specimens' identification was performed using a dichotomous key [29] to avoid possible colony contamination by the relative Ae. cretinus species, which is also present in some regions of Greece but at extremely low densities [22]. Larvae and adult rearing procedures of the established population were identical of that described for Cx.…”