NMCAW: Plymouth Field Staff Cheng Yang and Katie Powell
June 22, 2022
Weekly Update – June 27th – Mosquitoes Remain Below Average, First West Nile Found
July 6, 2022
A drier June has led to a decrease in adult mosquito numbers as we head into 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.
Thanks to below average precipitation in most parts of the District and a few other factors, mosquito numbers continued to dwindle in the third week of June. Across the seven county metro area the average number of human-biting adult mosquitoes collected in CO2 traps was lower than the previous week and similar to where it was at the end of May.
According to MMCD Assistant Entomologist Scott Larson, "human-biting mosquito counts were down significantly, with only 50 traps collecting more than 50 mosquitoes and only 1 trap had over 1000. Of course it was super hot on June 20, so that might also cause mosquitoes to seek shelter and avoid flying out in the open (to some degree, anyway)."
Another 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 have begun to emerge in northern parts of Anoka and Washington County, but not in many other areas. This coming week will better determine how many are out this year.
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 20th:
Surveillance is underway to detect mosquitoes that may be carrying diseases.
Brian F. from MMCD's Rosemount Facility collecting a sample using an aspirator.
Throughout the summer MMCD makes it a priority to find the species that are capable of carrying mosquito-borne disease. Our field staff uses a variety of surveillance methods in addition to sweep net collections and CO2 traps, which include aspirator collections, gravid traps, and other specialized traps. Most of these methods are intended to collect container breeding mosquitoes that are can carry diseases like West Nile virus and La Crosse encephalitis.
Two species of concern for their ability to vector La Crosse encephalitis are Aedes triseriatus and Aedes japonicus. According to MMCD Vector Ecologist Kirk Johnson, "aspirator sampling has indicated that both Ae. triseriatus and Ae. japonicus populations are developing as is typical. The Ae. triseriatus population is lagging about a week behind the average pattern and the Ae japonicus numbers are running slightly higher than average, so far. The cool start to the season is the logical explanation for the later increase in the Ae. triseriatus population."
The risk for mosquito-borne disease increases throughout the summer, so please take precautions and make sure you are wearing the right insect repellant!
For the latest updates on mosquito control, disease activity, and planned treatments, follow MMCD on Twitter or Facebook.
