Background

Mosquito larval control through the use of insecticides is the most common strategy for suppressing West Nile virus (WNV) vector populations in Connecticut (CT), United States. To evaluate the ability of larval control to reduce entomological risk metrics associated with WNV, we performed WNV surveillance and assessments of municipal larvicide application programs in Milford and Stratford, CT in 2019 and 2020. Each town treated catch basins and non-basin habitats (Milford only) with biopesticide products during both WNV transmission seasons. Adult mosquitoes were collected weekly with gravid and CO₂-baited light traps and tested for WNV; larvae and pupae were sampled weekly from basins within 500m of trapping sites, and Culex pipiens larval mortality was determined with lab bioassays of catch basin water samples.

Results

Declines in 4^th instar larvae and pupae were observed in catch basins up to 2-weeks post-treatment, and we detected a positive relationship between adult female Cx. pipiens collections in gravid traps and pupal abundance in basins. We also detected a significant difference in total light trap collections between the two towns. Despite these findings, Cx. pipiens adult collections and WNV mosquito infection prevalence in gravid traps were similar between towns.

Conclusion

Larvicide applications reduced pupal abundance and the prevalence of host-seeking adults with no detectable impact on entomological risk metrics for WNV. Further research is needed to better determine the level of mosquito larval control required to reduce WNV transmission risk.

The .zip file contains .csv data files corresponding to larval and adult mosquito and West Nile virus surveillance in Milford and Stratford, Connecticut, United States from 2019 - 2020. The data files are: 1) mosquito larval collections from catch basins in each town for each year of collection, 2) adult mosquito collections and arbovirus detections from gravid and light trap collections in each town for each year of data, and 3) multipe summary files of Culex pipiens collections in each trap type with corresponding larval sampling data. Briefly, the data was analysed using functions available in R packages for generalized linear mixed effects models. Please see the manuscript for specific methodologies and data restrictions.

To use this data set, someone would need working knowledge of R (or equivalent softwares); specific usage of each program is described in the associated manuscript. A solid foundation in vector-borne disease surveillance systems and statistical analyses is also recommended.