Weekly Update – May 20th – Spring Mosquitoes Already Above Average for 2024
May 29, 2024
Weekly Update – June 3rd – Mosquito Hot Spots Remain in Carver, Anoka Counties
June 11, 2024
The first few weeks of mosquito surveillance of 2024 show us above average, similar to how things looked in 2023.
Continuous rain has kept mosquito and black fly activity elevated as we head into the end of May and early June.
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.
We often emphasize the correlation between weather and mosquito activity, especially precipitation and the past couple of weeks have demonstrated that relationship. May was the third wettest month in the past 10 years with statewide rainfall totals sometimes two to three times the average. In the past week alone we've had at least one inch of rain somewhere in the District in 3 out of 7 days. All this precipitation has led to some heavy mosquito activity as each subsequent rainfall hatches more eggs. At the end of last week, staff from our Oakdale facility found several ponds teeming with larvae as seen in the dips pictured below:
Dippers full of larvae - left from Baytown and right from North St. Paul.
According to MMCD assistant entomologist Dr. Scott Larson, "Last week we collected our first adult Coquilletidia perturbans (cattail) mosquitoes which feels early. We also captured Culex tarsalis in every county of the District. The normal broods we expect after heavy rains aren’t really happening like they used to in the past." It's possible that three years of drought has decreased the number of floodwater mosquitoes so fewer hatched during this spring's heavy rainfall.
Black flies remain abundant in the typical hot spots along rivers and streams. Black fly treatments are difficult when river levels are high and staff aren't always able to access entry points to get on the water. As river levels decline, black fly treatments will continue.
Here are the mosquito trap counts from last Monday, May 28th:
Tick activity remains high and nymph activity is beginning to increase.
According to MMCD tick specialist, Janet Jarnefeld field staff are beginning to collect nymph ticks and in a normal year the peak season for deer tick nymphs is mid-June. Nymphal stage deer ticks are often as small as a poppy seed and can be difficult to find on people and pets. Due to their small size, nymphal stage ticks are one of the top concerns regarding Lyme disease transmission because they often go undetected and can remain attached to a host for several days. The longer a tick is attached, the higher the risk of disease transmission and for Lyme disease it is estimated that deer ticks need to be attached to their host for at least 24 hours before the pathogens that cause Lyme disease are spread.
The tick-risk meter is currently set to "Medium" due to an average number of adult deer ticks and low, but increasing numbers of nymph deer ticks.
The risk of mosquito-borne disease currently remains low. Last week 38 samples of adult mosquitoes were tested for West Nile virus and all came back negative.
Recently KARE 11 produced a story about the elevated numbers of mosquitoes this spring. Check it out below:
