Objective To investigate the current status of insecticide resistance and overwintering ecology of Aedes albopictus in Haiyan County, Zhejiang Province, and to provide a theoretical basis for effective control of mosquito population density and scientific prevention of dengue fever outbreaks.

Methods A cross-sectional study was conducted from June to July 2024, Aedes albopictus larvae were collected from five subdistricts (towns) in Haiyan County, and reared to adult mosquitoes in the laboratory. Insecticide resistance was tested using the WHO contact-cylinder method. Concurrently, data on insecticide usage in this area during 2023 covering three professional pest control agencies and the Patriotic Health Campaign Committees of each subdistrict/town responsible for routine vector control management, were collected. Additionally, from January to March 2024, water samples from different habitats and container types were collected for laboratory incubation. Information on the type of water collection site, water quality, presence of symbiotic organisms, and meteorological conditions at the time of collection was recorded simultaneously, and the incubated adult mosquitoes were identified to species.

Results In 2023, 15 kinds of public health insecticides were used in Haiyan County, and 80% of which contained pyrethroids. In 2024, Aedes albopictus showed resistance to 0.40% permethrin, 0.08% beta-cypermethrin, 0.40% beta-cypermethrin, 0.50% malathion, possible resistance to 0.03% deltamethrin, and susceptibility to 2.00% chlorpyrifos and 0.05% propoxur. A total of 982 samples were collected across three streets/towns, of which 966 were brought into the laboratory for rearing and observation. Aedes albopictus larvae or adults were found in 187 samples, resulting an overall positive hatching rate of 19.36% for Aedes albopictus eggs. Statistically significant differences in the hactch positive rates of overwintering Aedes albopictus eggswere observed across different months (12.89% in January, 18.24% in February, 26.39% in March), different habitats (21.94% in urban residential area, 9.79% in rural residential area, 26.96% in parks/scenic spots), different types of water accumulation (11.17% of fixed water accumulation, 8.72% of natural water accumulation, 27.98% of temporary water accumulation, 40.66% of discarded tires), different water quality (9.25% of clear water, 38.05% of turbid water), and different symbiotic organism scenrios (2.88% in habitats without symbionts, 21.35% in habitats with symbionts).

Conclusion In 2023, pyrethroid insecticides were extensively used for Aedes albopictus control in Haiyan County, Zhejiang Province, local mosquitoes have developed resistance to permethrin, beta⁃cypermethrin, and malathion. The hatching rate of overwintering Aedes albopictus eggs is strongly environment-dependent. High⁃positivity sites were characterized by early spring (March), parks/scenic spots, urban residential areas, discarded tires and temporary water accumulations, turbid water, and the presence of symbiotic organisms. In the future, it is necessary to continuously carry out resistance monitoring to guide the scientific and standardized use of insecticides. Targeted elimination of egg-bearing habitats—especially park/scenic spots, urban residential areas, discarded tires, temporary water, turbid water, and water with symbiotic organisms—should be completed before early spring (March) to maximize overall control efficacy.