Increased abundance of floodwater mosquito species over three seasons in Forshaga municipality, western Sweden

Abstract

Floodwater mosquitoes are a main cause of mosquito nuisance in several European countries, including Sweden. Since 2002, a large-scale mosquito control programme around the river Dalälven in eastern Sweden targets floodwater mosquito species such as Aedes sticticus. The current study was initiated due to citizen complaints about nuisance mosquitoes around Deje village in Forshaga municipality, a region situated at the river Klarälven in western Sweden. Over three years, 2010-2012, mosquito collections with CDC-light traps and morphological species identification were performed to determine the nuisance causing mosquito species and to describe the seasonality, abundance and species composition of mosquitoes in the area. Over the three years of collections at eight trap sites, mosquito abundance increased with a mean of 282 mosquitoes collected per trap-night in 2010, 702 mosquitoes per trap-night in 2011, and 1,367 mosquitoes per trap-night in 2012. The increase in abundance was mainly due to an increase of floodwater mosquitoes, with Ae. sticticus as the main species. Single traps collected over 5,000 floodwater mosquitoes at several occasions in 2011 and 2012. A correlation between river discharge exceeding 300 m3/s and an increase in floodwater mosquito abundance three weeks later when average air temperatures were around 15 °C could be seen. Interestingly, river discharge was the highest in 2010, however mosquito abundance was higher in both 2011 and 2012. Potentially, the increasing number of diapausing eggs available after each season has contributed to the amplification of the Ae. sticticus population in the region.