Insecticide resistance is one of the primary problems affecting vector control worldwide. Assessing the occurrence of resistant alleles and understanding their origin across the geographic range of vector species is crucial for effective resistance management. In populations of the mosquito Culex pipiens, point mutations conferring resistance to the insecticide diflubenzuron (DFB) were recently found across the Mediterranean basin. In this study, we investigated the possible occurrence of DFB resistance in Cyprus, where West Nile virus outbreaks have been documented in recent years. We sequenced a fragment of the chitin-synthase 1 gene carrying the resistant mutations in individuals collected from 18 populations of Cx. pipiens in Cyprus to investigate the occurrence of DFB-resistant alleles. We then assessed the evolutionary origin of DFB-resistant alleles by reconstructing the phylogenetic relationships between susceptible and resistant alleles found across the Mediterranean basin. Our screening revealed the occurrence of the I1043F allele in all the districts analyzed. Notably, a new gene codon underlying the I1043F allele was detected. To our knowledge, this has not been previously reported in areas with DFB-resistance alleles in Cx. pipiens. In addition, we observed that the I1043F alleles detected in Cyprus have a different genetic background from those reported in other geographic areas, such as Italy and Turkey. To our knowledge, this is the first time in which DFB resistance was revealed in Cx. pipiens populations occurring in Cyprus. Furthermore, we demonstrate that I1043F-resistant alleles have an independent origin in Cyprus, further supporting the hypothesis of a multiple independent origin of DFB resistance across the Mediterranean region. These results stress the need for regular resistance surveillance activities and the urgency of developing new mosquito control strategies.
The invasive Asian tiger mosquito (Aedes albopictus) poses growing health risks across Europe. In Switzerland, a preliminary field trial was conducted to assess the feasibility of integrating the sterile insect technique (SIT) into existing integrated vector management (IVM), which includes breeding site removal and application of biological larvicides. SIT involves repeated releases of irradiated sterile males, which mate with wild females, producing non-viable eggs and leading to population decline. Following a preliminary release test in 2022, a small-scale SIT trial took place in 2023 in Morcote, Switzerland. Approximately 150,000 sterile males were released weekly over a 45-hectare area throughout the entire mosquito activity season, from May to September. This SIT area also received routine IVM. Population dynamics were compared with a control area where only IVM was applied. Monitoring included egg counts, hatch rates, and adult female densities. Generalized additive mixed-effects models (GAMM) and generalized additive models (GAM) accounted for spatial, temporal, and random effects. Model selection used AIC, BIC, and Chi-square tests (significance at 5
BackgroundKnowledge of the distribution and abundance of disease-causing mosquito vectors is fundamental for assessing the risk of disease circulation and introduction. Aedes caspius (Pallas, 1771) and Aedes vexans (Meigen, 1830) have been implicated, to different extents, in the circulation of several arthropod-borne viruses (arboviruses). These two mosquitoes are vectors of Tahyna virus in Europe and are considered potential vectors of Rift Valley fever virus, a virus not present but at risk of introduction on the continent.MethodsIn this work, we analysed abundance data collected during West Nile virus (WNV) surveillance in northern Italy (Po Plain) via 292 CO2-baited traps to evaluate the distribution and density of these two non-target mosquitoes. We modelled the distribution and abundance of these two mosquito species in the surveyed area using two distinct spatial analysis approaches (geostatistical and machine learning), which yielded congruent results.ResultsBoth species are more abundant close to the Po River than elsewhere, but Ae. caspius is present in the eastern and western parts of the plain, linked with the occurrence of rice fields and wetlands, while Ae. vexans is observed in the middle area of the plain.ConclusionsPresence and abundance data at the municipality level were obtained and made available through this work. This work demonstrates the importance of maintaining and improving entomological surveillance programs with an adequate sampling effort.
Pyrethroids, targeting the voltage gated sodium channel (VGSC), are fundamental for the control of arboviral disease circulation. The spread of pyrethroid resistance among vector species represents thus a major public health concern. Culex pipiens is one of the most abundant European mosquito species and main vector of West Nile virus, leading cause of arboviral encephalitis worldwide. Despite this, monitoring of its resistance status and the understanding of underlying mechanisms are widely neglected. Herein, we performed an oligo-hybridization capture approach on 82 Cx. pipiens specimens from Italy and Greece to investigate the whole coding sequence of the vgsc gene for the presence of known and potential knock-down resistance (kdr) mutations associated with target-site resistance to pyrethroids in insects. Among the 26 non-synonymous substitutions revealed by the analysis, the super-kdr haplotype—i.e. the association of kdr-alleles 918T and 1014F, known for conferring a strongly enhanced resistance phenotype in Musca domestica – was revealed for the first time in mosquitoes. Three more potential kdr alleles were detected for the first time in Cx. pipiens and multiple kdr variants were observed for locus 1014, with allele 1014F, reaching frequencies > 80%. Overall, results depict a worrisome situation that could affect the ability to control West Nile virus outbreaks in southern Europe. To avoid this, resistance monitoring needs to be intensified and an enhancement of the diagnostic tool box for the easy detection of different kdr-variants (including in particular the super-kdr haplotype) and for subsequent functional studies on the resistance phenotype of detected variants, is required.
