Insect Update – Week of August 16th – Surveillance shows West Nile virus risk is present

Results from the August 16th surveillance show that floodwater mosquitoes are rare, but mosquitoes that can transmit West Nile virus are plentiful and more have tested positive for the virus

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.

In a typical year floodwater mosquitoes are the most likely to cause a nuisance to people spending time outdoors in the waning days of summer, but with our lack of rain this year we aren't seeing many. Instead the more prevalent mosquitoes are the species that prefer permanent water habitats like catch basins, containers, and other sources. According to MMCD assistant entomologist Dr. Scott Larson, "Anopheles and Culex species are dominating the collections. Maybe half of the CO2 traps had Anopheles quadrimaculatus." Larson also stated that he does not recalling seeing a map with such widespread Culex mosquitoes.

The prevalence of Culex in our area is cause for concern because, in Minnesota, these are the species most likely to carry West Nile virus. MMCD has seen an increase in calls from residents reporting dead birds, which is an indicator that the virus is active in our area. MMCD Vector Ecologist Kirk Johnson continues to test pools of mosquitoes and today another 9 samples have tested positive for West Nile virus including samples collected in Ramsey, Hennepin, and Anoka Counties.

As of this week 32 samples have tested positive for West Nile virus in almost every county in the metro, meaning the virus is active in our area and people should take precautions. 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 in the peak time of year for West Nile virus transmission.

Here are the mosquito trap counts from last Monday, August 16th: