10 Reasons to Visit the MMCD Booth at the Minnesota State Fair!
August 29, 2024
Weekly Update – September 4th – Mosquito Numbers Declining as We Enter September
September 11, 2024
Mosquito numbers increased again this week, but fell below the late August average.
The rainy summer is starting to catch up with us as mosquito numbers rebound and increase for the third straight week.
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.
Based on the 10-year average, it's common to see a slight uptick in mosquitoes during the last week of August as everyone heads outdoors to enjoy a last blast of summer. Surveillance from the week of August 27th shows another slight uptick in mosquitoes. The Twin Cities received above average rainfall again last month, with about 5.37 inches in the Twin Cities, keeping the trend of a wetter than normal summer. That frequent rain is finally starting to make an impact as some of the more common summer mosquitoes that have not been abundant this summer are starting to rebound. Also, some uncommon species are having a banner year.
According to MMCD Entomologist Dr. Scott Larson, "Most of the mosquitoes collected in the CO2 trap network were Aedes vexans mosquitoes. However, Culex mosquitoes are still abundant across the District. Culex salinarius, in particular, is having a very successful year, almost certainly the most abundant in District history. There was an average of 16 Cx. salinarius collected per CO2 trap last week. In the past 10 years, the highest weekly average we’ve ever recorded for this species was only 2.9, so 16/trap is a huge increase in abundance." Larson also explains that Culex salinarius mosquitoes were caught in sweep net collections by staff last week, which indicates they are attracted to humans. This causes some concern for West Nile virus transmission as Culex mosquitoes are the vectors of that disease.
Here are the maps from Monday-Tuesday, August 26th-27th:
West Nile virus remains a concern. More mosquitoes collected last week from around the District test positive.
West Nile virus continues to be a significant concern throughout the county as 377 cases have been reported in 38 states as of today, with numbers expected to grow during the next few months. In Minnesota there have now been five cases reported including the first two from residents in the metro area - one from Hennepin County and another from Scott County.
According to MMCD Vector Ecologist, Kirk Johnson, 5 mosquito samples collected last week have tested positive for West Nile virus (out of 46 that were tested). These were from Anoka, Dakota, Washington, Carver, and Ramsey Counties which shows the disease is present throughout the metro area. Overall risk to residents in the Twin Cities remains relatively low, with most mosquitoes testing positive being species that don't regularly bite humans. That being said, we are in the peak risk period for West Nile virus transmission, so it's still a good idea to take precautions including wearing insect repellent and removing standing water.
Another mosquito-borne illness has also been making the news lately - Eastern Equine Encephalitis or "EEE" (Triple-E). There have been 6 cases reported this year in 5 states so far in 2024, which is pretty typical for this rare disease. However, several cases and deaths on the East coast have led some communities in Massachusetts and Vermont to suspend evening activities. There has never been a human case of EEE in Minnesota, but this year there has been one in northeastern Wisconsin. The mosquitoes that are capable of carrying EEE (Culiseta melanura) are present in the District so MMCD works to take all preventative measures to ensure an outbreak is unlikely.
Several local news stations have reported on the current mosquito-borne disease situation including KARE 11 and WCCO. Here is Fox 9 providing an update on West Nile virus and EEE:
