Insect Update – Week of August 2nd – Low mosquitoes overall, high West Nile vectors
August 9, 2021
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August 23, 2021
Results from the August 9th surveillance show that overall mosquito numbers are very low, Culex mosquitoes are high, and more West Nile virus has been found
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 the dry summer continues in Minnesota, overall mosquito numbers remain low as we head into the middle of August. Results from last week's mosquito surveillance showed very low numbers of human-biting mosquitoes. According to MMCD entomologist Diann Crane, "the average mosquito per CO2 trap last week was 12 while the ten year average for that same time period is 118 per trap."
While overall mosquito numbers are down substantially, the numbers of Culex mosquitoes, the primary vector of West Nile virus in our area, is still high, though decreasing from previous weeks. MMCD vector ecologist Kirk Johnson reported that another pool of mosquitoes collected in Ramsey County tested positive for West Nile virus. This is the 12th positive sample so far this year.
Residents are advised to lower their risk of mosquito-borne disease by wearing insect repellent and avoiding peak feeding times of dusk and dawn. With lower annoyance mosquitoes, people may feel less inclined to take precautionary measures, but Minnesota is heading into the peak time of year for West Nile virus transmission.
Here are the mosquito trap counts from last Monday, August 9th:
Mosquito-borne Disease Update from MMCD
West Nile virus is not the only vector-borne disease risk that MMCD monitors; other, less common diseases like La Crosse encephalitis are monitored by disease species. According to MMCD Vector Ecologist Kirk Johnson, "the first La Crosse encephalitis cases of the year have been reported to CDC. There is one case in nearby Dunn County Wisconsin (county seat – Menomonie). Other cases are in North Carolina, Ohio and Tennessee. The Wisconsin case proves that even during a drought, LAC risk persists."
However, two important species for transmission of La Crosse encephalitis - Aedes triseriatus and to a lesser extent Aedes japonicus - are seeing declining numbers due in large part to the drought so risk for this disease remains low.
For the latest updates on mosquito control, disease activity, and planned treatments, follow MMCD on Twitter or Facebook.
