Assessing insecticide susceptibility of Culex pipiens linnaeus (Diptera: Culicidae) in the Aras River basin: implications for disease control.

BACKGROUND

Culex pipiens, the common house mosquito, is the main vector of important medical and veterinary diseases including West Nile fever. This disease is a neglected mosquito-borne disease in Iran, where migratory and resident birds act as the main reservoirs and human and horse act as dead-end hosts of the disease. The Aras River basin is identified as a high-risk area for West Nile fever outbreaks. Chemical vector control stands out as a key method for managing mosquito-borne diseases. So, it is necessary to evaluate the susceptibility of Cx. pipiens to insecticides recommended by the World Health Organization (WHO) in this region in order to control possible outbreaks of the diseases.

METHODS

Specimens were collected from various mosquito larvae breeding places in five villages along the Aras river basin that are politically separated but their agricultural fields are located close to each other. Detailed descriptions of the physical characteristics of each breeding site were recorded and documented. Susceptibility tests were carried out on adult mosquitoes according to WHO guidelines, utilizing five insecticides including DDT 4%, permethrin 0.75%, bendiocarb 0.1%, deltamethrin 0.05%, and malathion 5%.

RESULTS

The larval habitats were characterized as permanent, sunny areas with algae and vegetation, primarily consisting of muddy substrate and rice fields. The results of susceptibility tests showed that the Cx. pipiens mosquitoes were resistant to bendiocarb 0.1% and DDT 4% but were sensitive to malathion 5%. The results for the pyrethroid insecticides varied, with sensitivity to permethrin 0.75% and resistance to deltamethrin 0.05% (based on WHO guideline, with replicated tests).

CONCLUSION

Paddy fields serve as suitable biotopes for Cx. pipiens and some species of migratory birds, facilitating cohabitation and breeding. This close proximity of vectors and disease reservoirs increases the likelihood of West Nile fever outbreaks. Mosquito resistance to insecticides can lead to the failure of disease prevention and control programs. It seems that the agrochemical used in agroecosystems is the main cause of these resistances. Regional agricultural departments must regulate the use of agrochemicals to mitigate resistance in mosquito populations.