ABSTRACT
ObjectiveTo analyze the interannual fluctuation， seasonal fluctuation， habitat distribution and the correlation of the 3 monitoring indicators of Aedes albopictus in Yangpu District of Shanghai from 2017 to 2021， and to provide a scientific basis for A. albopictus control and rational use of the indicators. MethodsThe density surveillance data of A. albopictus recorded by Breteau index （BI）， Path index （PI） and the mosquito ovitrap index （MOI） from 2017 to 2021 in Yangpu District， Shanghai were compared. Microsoft Excel 2019 software was used for data summary and SPSS 25.0 software was used for statistical analysis. ResultsFrom 2017 to 2021， there were two months with BI>5， and the PI were all above the density control level of Class C， and there were nine months with MOI≥5. In 2017， BI was higher than in the other four years， with statistically significant differences （all P≤0.001）. MOI in 2017 and 2020 was higher than in 2019 （P=0.029， P=0.004） and 2021 （P=0.005， P=0.001）， with statistical significance. MOI for different types of habitats varied significantly， with a statistically significant difference （P=0.004）. A linear correlation was observed between BI and PI （r=0.462， P=0.010）. ConclusionBI， PI and MOI are used simultaneously to reflect the density of A. albopictus in Yangpu District of Shanghai. However， these three monitoring indicators show poor linear correlation. Comprehensively considering the scientific aspects of monitoring methods and seasonal fluctuations of indicators， it is suggested that MOI should be used as the main index to evaluate the density of A. albopictus. In the MOI， attention should be paid to factors such as the distribution of the habitats， the standardization of operating methods， and quality control， which are essential for enhancing the reliability of the MOI.
ABSTRACT
Objective To analyze the density, distribution and insecticide resistance of Aedes albopictus in Ningbo City in 2021, so as to provide insights into formulation of dengue fever control strategies. Methods Four administrative villages were randomly selected from each county (district) in Ningbo City from April to November, 2021, to investigate the indoor population density of Aedes larvae, and the Breteau index (BI) was calculated. The population density of adult mosquitoes was investigated in residential areas, parks/bamboo forests, waste tire stacking sites/waste stations/construction sites in each county (district). On June 2021, larvae of the natural strain A. albopictus were collected from epidemic sites of dengue fever in Ningbo City in 2018, and raised in laboratory. Then, larvae and female mosquitoes without blood feeding were selected for insecticide resistance bioassays, while insecticide-sensitive strains of A. albopictus served as controls. The resistance of A. albopictus larvae to deltamethrin, beta-cypermethrin, propoxur, temephos and dichlorvos using the impregnation method, and the medium lethal concentration (LC50) and resistance ratio (RR) were calculated. The resistance of adult A. albopictus to beta-cypermethrin, permethrin, deltamethrin, propoxur and malathion was determined using the tube bioassay, and the mosquito mortality was calculated. Results A total of 10 072 small water containers from 9 935 households were investigated in Ningbo City in 2021, and there were 1 276 containers with Aedes larvae detected, with an average BI of 12.89. Totally 1 422 mosquito nets were allocated and 954 female A. albopictus were captured, with an average net trapping index of 1.34 mosquitoes/(net·hour). Both larval and adult A. albopictus mosquitoes were found from April to November, and the density of larval A. albopictus peaked in September (BI = 21.21), while the density of adult A. albopictus peaked in August, with a net trapping index of 2.38 mosquitoes/(net·hour). The LC50 values of delta-methrin, beta-cypermethrin, propoxur, temephos and dichlorvos were 0.017 4, 0.000 9, 0.364 1, 0.038 1 mg/L and 0.001 6 mg/L against larvae of natural strains of A. albopicchus, with RRs of 49.66, 25.53, 9.65, 2.24 and 6.06, and the mortality rates of adult mosquitoes were 66.00% (66/100), 69.39% (68/98), 25.00% (25/100), 98.97% (96/97) and 100.00% (98/98) 24 hours post-treatment with 0.08% beta-cypermethrin, 0.03% deltamethrin, 0.4% permethrin, 0.05% propoxur, and 0.5% malathion for 24 h, respectively. Conclusions A. albopictus is widely distributed in Ningbo City, with a high population density and presents high-level resistance to common pyrethroid insecticides. The population density and insecticide resistance of A. albopictus requires to be reinforced.