[Surveillance of populations in Jiangsu Province in 2020].

OBJECTIVE

To investigate the seasonal population fluctuation and the resistance of populations to common insecticides in Jiangsu Province in 2020, so as to provide insights into vector-borne infectious diseases control.

METHODS

One village was randomly sampled from each of Xinbei District of Changzhou City and Zhangjiagang County of Suzhou City in southern Jiangsu Province, Hai'an County of Nantong City and Yandu District of Yancheng City in Central Jiangsu Province, and Suining County of Xuzhou City and Sihong County of Suqian City in northern Jiangsu Province during the period between May and October, 2020. A small ponding container was sampled, and larval mosquitoes were collected using straws once each in early and late stages of each month. All larvae were bred in laboratory to adults for population identification. In addition, larval breeding were observed in all small ponding containers in and out of 30 households that were randomly sampled from six surveillance sites, and the larval mosquito density was estimated using Breteau index. Larval mosquitoes were sampled around Cuiyuan New Village in Jintan District of Changzhou City, and bred in laboratory to the first offspring generation, and the susceptibility of adult female mosquitoes to deltamethrin, lambda-cyhalothrin, malathion, and propoxur was tested using the filter-paper bioassay recommended by WHO.

RESULTS

A total of 1 165 larval mosquitoes were captured from small ponding containers in six surveillance sites of Jiangsu Province in 2020, and all were identified as following eclosion. The largest number of larvae captured was found in July. A total of 1 152 households were investigated in six surveillance sites, and the mean Breteau indexes were 9.58, 13.20, 13.71, 13.20, 12.18 and 5.58 from May to October, respectively, while a high transmission risk was seen in Xinbei District of Changzhou City, with a higher Breteau index than in Suining ( = 23.667, = 0.001) and Sihong ( = 22.500, = 0.003) counties. The field-captured from Cuiyuan New Village in Jintan District of Changzhou City remained sensitive to malathion, but was resistant to propoxur, and developed high-level resistance to deltamethrin and lambda-cyhalothrin.

CONCLUSIONS

was present in southern, central and northern Jiangsu Province in 2020, and the larval density peaked in July. captured from Cuiyuan New Village in Jintan District of Changzhou City has developed high-level resistance to pyrethroid pesticides.