Mosquito super emergence

Has anybody noticed that there are more than a few mosquitoes out right now?

Holy cow! We had what can only be described as a mosquito super emergence this past weekend (August 6-7) in south central Michigan. One on-the-spot observer (on-the-spot blood donor may be more accurate) reported the super emergence began sometime last Friday (August 5). By Sunday afternoon, we had clouds of the hungry little devils at my home just south of Mason, Mich., in Ingham County. My wife describes them as “biblical”: she and I are thinking this is the worst we have ever seen them and we live in a swamp that routinely produces prodigious numbers of mosquitoes. Not only are these skeeters swarming in unprecedented numbers, they are hungry, frenzied and determined biters. They will bite you early in the morning, during the day and at night. A few unprotected moments out in their midst can easily yield a dozen or more itchy bites.

Since Monday morning (August 8), many people have called the lab seeking an explanation for this sudden population explosion. The answer is quite simple: The super emergence is the result of the heavy rains the area experienced on July 27-28. My rain gauge had that two-day, unofficial total at just over 8 inches. Without a doubt, this amount of rain filled every dried-up ditch, depression, tree hole and other natural and manufactured water-holding hollows with enough water long enough to produce a batch of mosquitoes. Many callers have asked how long will they last and are somewhat disheartened to hear they will have to contend with them for another two to three weeks, a very dim prospect indeed.

Michigan is blessed with nearly 60 species of mosquitoes. These can be roughly divided into two groups: spring mosquitoes and summer mosquitoes. Spring mosquitoes are species that typically develop in snow melt pools and produce one generation per year. Summer mosquitoes are opportunists that will produce multiple generations during the summer as long as there is enough standing water for their larvae to develop in. At least three species of summer mosquitoes joined forces to make up the super emergence. All three can be described as floodwater mosquitoes. Making up this trifecta of misery are the three-striped mosquito, Aedes trivittatus; the inland floodwater mosquito, Aedes vexans; and the giant gallinipper, Psorophora ciliata.

Three-striped mosquito larvae develop in flooded woodlands, marshes, open pools and woodland pools and low lying areas along streams. These larvae develop very fast in the hot summer sun. The combination of warm nights and daytime temperatures in the 80s and 90s will produce Ae. trivittatus adults in as little as five days. It’s a good thing these mosquitoes don’t travel far from their breeding areas because they are persistent, aggressive biters, often attacking victims in a swarm-like manner. They are active during the day and do not hesitate to bite in bright sun or open areas. Most people who encounter them find their bites much more painful and irritating than other mosquitoes.

Aedes vexans is sort of a spring and summer hybrid mosquito that develops in snow melt water in the spring, but then acts like a summer mosquito that produces multiple generations as long as rainfall maintains or restores its breeding areas. Fall broods can extend well into September and these late season broods can be sizeable when heavy rainfall occurs. Almost any temporary water will support Ae. vexans larvae, but they seem to prefer unshaded pools and roadside ditches. Ae. vexans and Ae. trivittatus commonly share breeding areas in the summer. However, unlike Ae. trivittatus that does not travel far from its breeding areas, Ae. vexans shows a willingness to disperse and be a nuisance far from where its larvae developed.

The last member our super emergence trifecta is the giant Psorophora ciliate, also known as the gallinipper. Gallinippers are the largest mosquitoes found in Michigan. They have bushy legs with white stripes and these white stripes have led many people to believe that we have been invaded by Asian tiger mosquitoes, which also have white stripes on their legs. The key difference between the two is size: Asian tiger mosquitoes are small, whereas Psorophora ciliata is a huge, almost wasp-sized mosquito. Gallinipper larvae are predaceous and develop in many of the same areas where Ae. vexans and Ae. trivittatus larvae occur. Gallinipper larvae are reported to eat the larvae of both Ae. vexans and Ae. trivittatus. So, one might consider them a beneficial insect, but their presence is a mixed blessed at best because the females are persistent and painful biters, attacking any time during day when their haunts are invaded. Their mouthparts feel like telephone poles being shoved into your skin when they bite.

Coping with these super emergence mosquitoes parallels those recommendations for other mosquitoes. The best way to avoid being bitten is to simply stay indoors. For those of us who must venture outside, loose fitting clothing and repellents containing DEET can be effective in keeping the swarms from biting. I have found that full coverage of repellents is essential. Any exposed skin that has not been treated with repellent is sought out, discovered and attacked. I’m trying to figure out how to treat my eyeballs with the stuff without going blind. Propane-fired foggers or ULV (ultra low volume) sprayers can also be used to kill the adult mosquitoes in yards. If they get much worse, I am going to seriously consider purchasing one of these: a SOLO 450/451 ULV Cold Mist Fogger.

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