Assessment of pyrethroid resistance and Wolbachia prevalence in pathogen-related mosquito species from southwest Germany

The increasing incidence of arboviral diseases in Europe, driven by the expansion of mosquito vectors due to globalisation and global warming, poses a growing threat to public health. Notably, the invasive tiger mosquito Aedes albopictus, a primary vector of dengue, has been rapidly expanding its range, with outbreaks becoming more frequent in various parts of the world. Insecticides targeting adult mosquitoes are commonly employed as response and protective measures for vector control, but the effectiveness of such interventions may be undermined by rising insecticide resistance, a phenomenon increasingly reported worldwide. Another promising avenue for vector control is the use of Wolbachia, an endosymbiotic bacterium capable of reproductive manipulation in mosquitoes, offering potential for population suppression. We evaluated permethrin (a pyrethroid insecticide) resistance in key mosquito species, including Aedes and Culex, collected from Germany through generation of LC50 curves utilising topical exposure assays. Additionally, the prevalence of Wolbachia in these populations was determined via PCR amplification of the 16S rRNA gene, followed by sequencing of selected samples. All Aedes populations tested exhibited susceptibility to permethrin, whilst a potential trend toward resistance was observed in the Culex pipiens complex, a vector of West Nile virus. However, low numbers of field-caught Ae. albopictus and Ae. japonicus preclude firm conclusions about resistance in these species. Furthermore, Wolbachia was detected across all tested mosquito populations, marking the first recorded presence of Wolbachia in Ae. japonicus. These findings highlight the continued efficacy of pyrethroids against Aedes populations in Germany and underscore the need for ongoing surveillance of insecticide resistance, particularly in Culex species. Additionally, the detection of Wolbachia in native and invasive mosquito populations opens new avenues for the exploration of biological vector control strategies in Europe. This study provides crucial preliminary data supporting the strategic use of pyrethroids and Wolbachia for arboviral outbreak prevention in Germany.