Weekly Update – July 16th – Have We Passed the Mosquito Peak for 2024?
July 25, 2024
Weekly Update – July 30th – West Nile Virus Activity Increases
August 8, 2024
The week of July 23rd saw some of the lowest mosquito counts since the beginning of the year.
Mosquito numbers continue to decline as we head into the later months of summer and see slightly drier conditions.
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.
Overall mosquito numbers dropped sharply last week, and there are likely multiple causes. For one, it's been drier the past several weeks with fewer inch or more rain events in July than in June. For another, it was raining last Monday night when our traps were set out so it's possible fewer mosquitoes were collected than would normally have been. Finally, the 10-year average indicates that mosquito numbers drop sharply at the end of July and this year is following that pattern.
According to MMCD Entomologist Dr. Scott Larson, "Even though all the groups of mosquitoes were down last week, Culex mosquitoes were still very common all across the District. Some of the later season species are starting to appear in greater numbers, so it really feels like the summer is winding down a bit."
Black flies are finally starting to decline along the rivers in the south metro, though several traps are still collecting high numbers, especially in southern Carver and eastern Dakota counties.
Below are the maps from Monday-Tuesday, July 22-23rd:
Mosquitoes in several counties test positive for West Nile virus
As we've mentioned in past weeks, the number of Culex mosquitoes, which are the primary vector of West Nile virus in our region, have been above average this year. Until recently, most samples that have been tested for the disease came back negative, but in the past week eight new samples have tested positive. The positive samples from last week came from mosquitoes collected on either July 10th or July 17th and they were located in Anoka County, Washington County, Ramsey County (3), Carver County (2), and Dakota County. These are in addition to the positive samples found in Anoka and Dakota Counties earlier this summer.
According to MMCD Vector Ecologist, Kirk Johnson, "The increase in the number of positive samples last week follows a typical pattern for [West Nile virus]. Amplification of West Nile virus is strongly influenced by temperature, warmer temperatures increase the rate of amplification. We usually observe an increase in the WNV infection rate in mosquitoes one to two weeks after temperatures rise."
While the infection rate for the year is still low, it's clear that West Nile virus is present in our area, so it is recommended that residents take the usual precautions which include wearing insect repellent, avoiding peak mosquito feeding times, and removing standing water.
It's Event Season and MMCD Has a Full Schedule!
The last few weeks of summer are packed with county fairs, city festivals, and the Minnesota State Fair at the end of August and MMCD will be at many events throughout the next few weeks. Recently, we tabled at the Scott and Anoka County Fairs and appeared in the Slice of Shoreview and Leprechaun Days (Rosemount) Parades. Here are some of our upcoming events:
- Today - Sunday, August 4th - Washington County Fair
- Friday, August 2nd - Minnesota Mosquitoes at the Oakdale Library
- Sunday, August 4th - Canadian Days Parade (Little Canada)
- Monday, August 5th - Sunday, August 11th - Dakota County Fair
- Wednesday, August 7th - Sunday, August 11th - Carver County Fair
- Friday, August 9th - Sunday, August 18th (Weekends) - Game Fair
- Saturday, August 10th - Stockyard Days Parade (New Brighton)
At tabling events we will have LIVE mosquito larvae along with microscopes, handouts, and lots of great educational materials. At our parades we will have a giant, inflatable mosquito and you may even come across our mascot, Vectoria! Below is a photo of staff at the Slice of Shoreview Parade and Ramsey County Commissioner Nicole Frethem who donned the costume for the day:
