May 27, 2021 at 1:43 p.m.
Mosquito season starts in the Northwoods
Not all control methods are effective
Mosquito season starts in the Northwoods
Mosquitos are true flies, meaning they only have two wings, unlike many other insects that have two sets of wings. There are more than 3,600 species of mosquitoes on the planet, with 175 of them in North America. Of those, 57 species are known to be in Wisconsin at this time, with the possibility there may be a few more that are, as yet, unknown. Mosquitoes have been around since the Jurassic period
Mosquitoes need water to complete their life cycle. The cooler that water is, the longer it takes mosquitoes to mature through their four substages, on instars, as they move from egg form to pupae form. The time it takes also varies by species as well as water availability.
Mosquito larvae and pupae are aquatic and like still or slow-moving water. Most of the larvae feed on plant debris, although a few are predators.
Each mosquito species is different in many ways. Their preference for certain water conditions is one of the things that differs from species to species. Quality of water, location of the water source and longevity of the water body are all factors to which certain species respond differently.
Mosquitoes have followed man across the globe, Liesch said, because humans create good habitat for them. From the earliest times of irrigation ditches and pit latrines, mosquitoes have found suitable homes near humans. We continue to move mosquitoes today. International movement of tires, for example, has brought non-native invasive mosquito species to Wisconsin, according to Liesch. The Asian Rock Pool Mosquito, which is also not native here, was found in a hyacinth globe by a Madison resident who brought the water globe to Liesch for identification. Whether mosquitoes have been transported by humans, or simply followed humans as they created suitable habitat, their coexistence has caused problems for humans and other animals.
Mosquito bites are something all to familiar to most in the Northwoods. But not all mosquitoes feast on humans or animals. Only females take blood meals for protein for egg production, with males feeding instead on nectar. Males can even act as pollinators in some cases.
How mosquitoes find humans
Liesch said mosquitoes key in on many things which help them find humans or other animals for blood meal. Mosquitoes can detect carbon dioxide from up to 30 feet away. They can also get visual cues from that distance. They can also detect odor and heat from a few feet away. So they may use a carbon dioxide cloud to determine the direction in which they may find a blood meal, then use the heat from a human's body to hone in on that meal.
Several factors can determine whether or not a person will be a "mosquito magnet," or even be largely left alone, Liesch said. Genetics, skin temperature and metabolism are all contributing factors. Persons with a higher body temperature may look like a better target than those with a lower body temperature, for instance. CO2 and other chemicals can be exhaled and chemicals can be excreted through skin that would make one person seem like a better meal than others. Skin microbiome, blood type and even pregnancy can make a person a "mosquito magnet," too.
The mosquito bite
The mosquito's sucking mouth parts are actually quite involved. The many parts of their mouth all work in unison to make them an effective eater. It may seem as though the mosquito simply sticks its mouth into the skin and immediately starts to draw blood. However, as was shown in a video Liesch provided during his talk, the mouth parts actually move around under the skin in search of a blood vessel, sticking into that vessel once it is found.
Mosquito saliva contains over 100 different proteins. It can also contain anticoagulants, which keep blood from clotting while they eat, and vasodilators. Liesch said the "recipe" in the saliva differs from species to species, In humans, both sensitization and desensitization to mosquito bites are possible. Bites can also involve both acute responses, occurring in under 20 minutes, and longer responses, such as those bites that itch for days.
Types of mosquitoes
Liesch said there are four basic functional groups of mosquitoes. The snowmelt group is the earliest to arrive, using the melting snow as their water source. These mosquitoes have one generation per year and are gone until the next year.
The next group is the permanent pool group. They rely on standing water, and can actually do better in urban and suburban areas in drier years. They utilize the sewage system as a water source, and in dry years, flooding rains do not wash away eggs and larvae.
Floodwater mosquitoes are those that use ephemeral pools and can be abundant in rainy years. These mosquitoes also have a long flight range of five to 20 or more miles.
Container breeders are those that will use either a natural container, such as a hollow tree trunk, or a manmade container such as a tire, birdbath or other container that collects water, as their water source. These can be vectors for some diseases.
Liesch spoke briefly about mosquito-borne diseases as well. While diseases such as malaria, West Nile virus, yellow fever, Zika Virus, Dengue and Chikungunya are all possible from certain species of mosquitoes in our area, tick-borne diseases cause many more issues for humans, he said.
Mosquito control
Liesch said there are many myths about mosquito control and warned against the "illusion of causality." This means, a person may think because they ate a certain thing, or did a certain thing, they were bothered less by mosquitoes when, in fact, it may have been some other factor, such as mosquito presence being low in an area or at a time of year.
Managing habitat for mosquitoes is important in controlling them, Liesch said. People should attempt to keep standing water at a minimum. This could be anything from toys in the yard to empty flower pots, tarps that collect water, or even bird baths that are not changed regularly.
Dense vegetation, too, can serve as a good resting area for mosquitoes. Plants that overhang water can become an easy food source for larvae as well.
At times, avoidance is the best tactic, Liesch said. Staying indoors, or on a screened in porch can be a good idea. Using fans to keep air moving could send mosquitoes off in another direction. Personal protective clothing, while not always ideal for many hot summer days, will also help.
Liesch then turned to repellents. There are many good repellents on the market, but users should be sure to read the directions. Knowing how to apply, and when to reapply, repellents will ensure their effectiveness. He recommended only using EPA-approved repellents, as those have been proven effective. These would include products containing DEET, Picardidin and IR3535.
When looking at area repellents, some did not stand up to the task, he said. Citronella candles and mosquito coils were only effective at very short distances, approximately five feet. Pyrethroid-based area repellents, though, did prove effective and worked very well, according to the studies Liesch referenced.
Liesch also spoke about insecticides, both larvicides and adulticides. Larvicides, he said, acted over a longer period, where adulticides may need to be reapplied throughout the season in order to be effective.
Reapplication could be problematic. These adulticides are not specific to mosquitoes and will kill other beneficial insects. Studies have shown this can even have an effect on birds and other animals that use those insects as a source of food. These, Liesch said, pose major concerns and are pyrethroids that last only approximately two to four weeks.
Liesch also said, even insecticides have limitations. Those dealing with mosquitoes should have realistic expectations. Living "mosquito-free" may simply not be a possibility, he said. Also, with the long flight range of some mosquitoes, a property that has been treated may see mosquitoes fly in from another area shortly after treatment. Also, an abundance of good mosquito habitat may trump any treatment attempts.
Failed control attempts
Diet and supplements, though touted by some as mosquito control techniques, are not effective, he said. The consumption of alcohol, however, does seem to work to make a person a better target for mosquitoes.
Bug zappers do kill some mosquitoes, but kill indiscriminately. Some research has found 95% of insects killed are not mosquitoes. There is also no evidence to support that the use of these zappers reduces the biting rates for those in the area.
CO2-based traps are also somewhat ineffective, Liesch said. They do catch mosquitoes, but may also increase the presence of them in an area, leading to little impact on the bite rate for humans and other animals.
Yeast traps, sonic mosquito repellents, and even more "natural" controls such as birds, bats and "mosquito plants," do little to limit the bite rate of mosquitoes, he added.
Lastly, Liesch recommended against using home remedies such as mouthwash solutions or fragrances. Most of them have no effect, he said, and those that have some effect are very short-lived. Essential oils were one of the remedies he said may work, but only for a very short time, as in for ten minutes at a time.
Liesch's full presentation can be found on the UW-Madison, Extension, Horticulture YouTube Channel. All of the webinars in this series will be available on that channel once they have been recorded.
Beckie Gaskill may be reached via email at [email protected].
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