While most of us think of mosquitoes as an annoyance because of their blood sucking bite, we often times forget the greatest concern is their ability to transmit disease. While not necessarily a huge concern for Ohioans, malaria remains one of the most severe public health problems worldwide that’s spread through the bite of the mosquito. Encephalitis, a concern for not only humans but also in the horse population, is a more common disease carried and spread in Ohio by mosquitoes. Who can forget how West Nile virus was quickly spread around the country by both mosquitoes and birds back in the early 2000’s? And, in fact, as recent as early in June 2017 Franklin County Public Health officials reported finding a West Nile infected mosquito pool in Norwich Township near the Columbus suburb of Hilliard. In addition, Canine heartworm, a serious and potentially fatal disease in dogs results from a nematode that is transmitted by several species of mosquito.
While the discomfort of a mosquito bite or the fear of receiving a disease from a mosquito bite is a legitimate concern for humans, perhaps a greater concern is that of humans infecting a mosquito with a disease or virus that the human might be carrying. Recent concerns regarding the Zika virus is an example.
Humans can infect mosquitoes
Today, there are no known cases of Zika actually being transmitted within Ohio. In fact, as of June 21, 2017 there were no local mosquito-transmitted cases of Zika in the continental U.S., but there have been approximately 140 travel-related cases reported this year. Concerns arise with the potential for a human carrier of one of the travel-related Zika cases to be bitten by a virus free Asian tiger mosquito (Aedes albopictus) that then has the ability to take the virus from the human carrier and pass it on through its bite to other humans. Thus, the risk is that a disease free Asian tiger mosquito population in Ohio could suddenly become an infected population with the ability to spread the disease throughout the continental U.S.
All that being said we obviously have valid health reasons that go beyond just suffering from an annoying bite for controlling the mosquito population.
Interrupt their breeding cycle
While there are several pesticide options available for controlling mosquitoes, the best solution is to eliminate the population by keep them from reproducing. Mosquito eggs require moisture in order to hatch, and once they do most species of mosquitoes will only fly up to a few miles from where they hatch. If standing water is avoided or eliminated in the surrounding area there will be few mosquitoes to even be concerned with.
All sources of standing water must be located and eliminated or refreshed weekly. That includes the obvious ones like old tires, kids’ toys, and flower pots as well as the less obvious sites like clogged house spouting or the hollow of a tree stump. Kids’ wading pools and bird baths should be replaced with fresh water weekly. Rain barrels should remain covered at all times. Even an over irrigated lawn can provide enough standing water to allow mosquito eggs to mature and hatch.
Lifecycle ranges from 10 days to 10 months
While given the right moisture conditions mosquito eggs can hatch only 2 to 3 days after being laid, they can also remain dormant for months and then after being flooded hatch just a few days later. Once hatched the larvae feed on small bits of organic matter in the water and mature into adults 7 to 10 days later. The adults can live for three weeks, laying anywhere from 1 to 400 eggs at a time.
Pesticides such as Dibrom or malathion distributed in foggers or misters are effective at killing adult mosquitoes but do nothing for controlling larvae or eggs that have yet to hatch. There are also several more pesticides available to licensed, certified pesticide applicators for foggers or misters.
Where it’s impossible to eliminate all standing water, controlling the larvae in the water becomes the next best option. Several larvicides are available for treating standing water including products like Bt or Altocid.
Residual sprays can be effective for homeowners to accomplish short term relief and control of adult mosquitoes. These sprays can be applied as barrier treatments to tall grasses, weeds, shrubs, fences, playgrounds, residences, or even subdivisions to help reduce the adult populations. These can remain active for several days to several weeks, but factors such as rain, high temperatures or exposure to strong sunlight may reduce their length or activity. Pesticides such as Sevin, naled, pyrethrins and malathion are labeled to be used in these situations.
Inside, most any pesticide sold for the control of flying insects indoors can be effective. These products commonly include pyrethrins or synthetic pyrethroids.
Repellents such as DEET can protect people from mosquito bites for one to five hours depending on a variety of factors including perspiration and the number of mosquitoes in the area.
Repelling devices, plants, traps or zappers are seldom effective
Research suggests that bug zappers, electronic or ultrasonic repellent devices and scented or repellent plants are not effective in significantly reducing mosquito populations.
A varied approach is required for effective mosquito control!
While avoiding the annoying bite of the mosquito may be the motivating factor, mosquito control is important for reducing the spread of disease. While seldom considered, it’s equally important that humans that may carry a disease such as Zika don’t allow themselves to be bitten in order that the disease is not spread further by infecting otherwise non-disease carrying mosquitoes. It takes a combination of methods to accomplish mosquito control.
It’s most important to eliminate the environment which allows mosquitoes to reproduce - that is standing water! Since mosquitoes don’t travel great distances, control of adult mosquitoes with strategic use of premises or area applied pesticides is effective at temporarily knocking down adult populations. Repellents can protect people for short periods of time from mosquito bites when used correctly.
- Stan Smith, PA, OSU Extension, Fairfield County