Weekly Update – June 20th – Mosquitoes Decline Heading into July
June 29, 2022
Weekly Update – July 5th – Cattail Mosquitoes Responsible for Surge in Some Areas
July 13, 2022
Not much rain and not very many cattail mosquitoes means that overall mosquito numbers stayed low as we began July.
Every Monday night starting in mid-May through September, the Metropolitan Mosquito Control District sets out a variety of mosquito and black fly traps throughout the district and employs a network of sweep net collections done by employees and volunteers. Any insects collected are brought back to our lab on Tuesday to be identified throughout the week with maps published to show current mosquito and black fly activity.
As we head into the time of year which is usually the peak season for adult mosquito activity, MMCD surveillance data indicates that across the District mosquito numbers are similar to where we were this time last year and significantly below the 10-year average.
According to MMCD Assistant Entomologist Scott Larson, "three CO2 traps had over 1000 mosquitoes each and only a handful had over 300. I think the graph [above] explains things as well as anything (there’s ~600 fewer mosquitoes on average in each CO2 trap compared to the 10-year average)."
One big reason for the low overall count was that cattail mosquitoes (Coquillettidia perturbans) are not emerging at the same levels as they usually do this time of year. This species of human-biting mosquitoes overwinters as larvae and emerges once per year, usually right around now (end of June, early July). Due to last year's drought the MMCD entomology lab predicted that cattail mosquito numbers would be about half what we collected in 2021 and about one fifth collected in 2020. Cattail mosquitoes were present on the border of Carver and Hennepin Counties and northern Washington County, but not in many other areas.
Black flies saw declining numbers in most traps compared to the previous week and we expect the decline to continue as we head into the time of summer when they are less active.
Here are the mosquito trap counts from last Monday, June 27th:
First mosquitoes test positive for West Nile virus in Hennepin County.
From June 22nd trap collections we found our first mosquito sample of the year that tested positive for West Nile virus. A gravid trap in Hennepin County collected Culex mosquitoes which were tested and subsequently found to be positive for West Nile virus, using the RAMP test method.
According to MMCD Vector Ecologist, Kirk Johnson, "temperatures in the forecast for the next ten days are warm enough to expect additional amplification of WNV and positive results from mosquitoes we collect will be more common over the coming weeks." Residents are advised to take precautions by using insect repellent, wearing long sleeves and pants, and avoiding peak feeding times of dawn and dusk.
For the latest updates on mosquito control, disease activity, and planned treatments, follow MMCD on Twitter or Facebook.
