Floodwater mosquito abundance before and after initiation of mosquito control in Forshaga municipality, western Sweden

Abstract Floodwater mosquitoes cause extreme nuisance and are the target for mosquito control in several European countries. In Forshaga municipality, western Sweden, high abundance of the floodwater mosquito Aedes sticticus has been reported in past years. This study describes mosquito abundances in Forshaga before and after initiation of mosquito control using VectoBac G ® , a larvicide based on the pre-toxins of Bti, administered by helicopter. Adult mosquitoes were collected with CDC-miniature light traps baited with carbon dioxide, and larval counts were performed in flooded areas. Both EU and Swedish national regulations determine when mosquito control can be used, and in 2019 abundance of adult mosquitoes reached the national requirement to initiate mosquito control the following year. In 2020 and 2021, flooding caused by the spring-flood in river Klarälven and rainfall induced hatching of floodwater mosquito larvae. In both years larval abundance reached the requirement to perform a mosquito control action. Both control actions were successful with >97% decrease in larval abundance and <1,000 adult mosquitoes collected per trap-night. The Bti-applications did not affect the abundance of non-floodwater mosquitoes; thus, it controlled the extreme nuisance without impact on mosquito community as a whole.