Beware the Mosquito!!

— Written By Bill Lord and last updated by Margaret Green

Summer is winding down, but North Carolina’s heat, humidity, and spotty rainfall are still with us. Heat, humidity, and standing water bring us one of summer’s less pleasant features, the mosquito. There are at least 60 species of mosquitoes living in North Carolina, and while mosquito bites can be unpleasant (and itch), bites can transmit disease organisms to people and domestic animals. Prior to 1900 malaria was wide-spread in North Carolina. It is said that more soldiers died in the civil war from malaria and related diseases than from combat. While malaria has been eradicated from the Southeastern United States, there are several mosquito-borne diseases that we need to be aware of and take seriously including West Nile virus, Eastern equine encephalitis, La Crosse encephalitis, and Chikungunya, a new mosquito-transmitted virus
The name ‘malaria’ derives from ‘bad air’, as the ancients thought that bad smelling air associated with swamps and drains caused malaria. We now know that it is not the bad air but the standing water that creates conditions in which mosquitoes can breed, and once they breed, mosquitoes seek out warm blooded hosts to feed on. Natural swamps and streams are usually not good places for mosquitoes to breed because water keeps moving in streams and swamps and the natural biodiversity of plants, insects, fish and amphibians found in swamps means there are plenty of natural predators in place to eat mosquito adults and larvae. Large storms, such as hurricanes, may disrupt this system and allow mosquito populations to rise rapidly in isolated pools of water. Human activities are much more likely to contribute to mosquito problems since mosquitoes can breed in any standing water, even in gutters and flower pots.
The first line of defense against mosquitoes is eliminating standing water around the home and landscape. Flower pots should not have water standing in dishes underneath the pots. Pet and livestock water bowls should be emptied and refilled regularly. Bird baths and water gardens should be flushed, treated, or in the case of water gardens, stocked with fish, specifically mosquito fish or Gambusia. Provide habitat for frogs, dragon flies, paper wasps, birds and bats – they all eat mosquitoes. Many people are surprised to see paper wasps on the list of mosquito predators. Paper wasps feed on nectar as well as other insects, including worms, caterpillars, flies, and mosquitoes. A study performed in the late 1950s by N.C. State entomologists found that providing paper wasp nesting sites around tobacco fields allowed the wasps to feed on tobacco bud worms and eliminate the need for insecticidal sprays. Purple martins and bats are known to eat large quantities of mosquitoes, so providing nest boxes for these two species will help with natural mosquito control.
If you have standing water in water gardens or in difficult to reach places such as flexible drain pipes attached to downspouts there is a natural pesticide available to control mosquitoes. There are several products formulated as “donuts” (“dunks”) or as granules that contain the bacterium Bacillus thuringiensis israelensis or “Bti”. This bacterium kills mosquitoes, but does not harm fish, birds or other wildlife. The “dunk” versions are well-suited for small breeding sites (100 sq. ft. or less) and will control mosquito larvae for about 30 days.
Chemical control of mosquitoes primarily targets the adult. Outdoor foggers will keep mosquitoes away for several hours, but once the chemical dissipates, mosquitoes may return to the area. Spraying thickets or shrubs along the perimeter of your yard helps reduce the population of mosquitoes that rest in these areas. However, some species of mosquitoes may move readily back into these areas from surrounding untreated places.
Insecticides are available for controlling larvae, but their application in either large bodies of water or small artificial breeding sites can be difficult and expensive, particularly for an individual homeowner. Control programs targeting mosquito larvae are best left to trained individuals in county or local government agencies. Most of these chemicals are not selective and some may even harm beneficial insects and other non-target organisms. Furthermore, use of these chemicals will provide only temporary reduction in mosquito populations. Modifying or eliminating breeding sites is the only long-term solution to severe mosquito problems.
To eliminate breeding sites first discard anything in your yard that can hold water, or be sure to ‘tip’ the water out regularly. If you use rain barrels cover the barrel with window screen to keep mosquitoes out. Treat ornamental fish ponds or waterfalls with Bti or ‘mosquito dunks. Discard flower pot saucers and flush out bird baths weekly. Be aware that boats and campers stored outdoors can collect water after rainstorms and should be covered so that no water ponds in the covers. Swimming pools make great mosquito habitat if abandoned or neglected. During the housing crisis many local governments stocked abandoned swimming pools with mosquito fish. Make sure all drain pipes actually drain and do not hold standing water. Fill tree holes to keep them from becoming breeding sites.

Finally, install and maintain tight fitting screens and the door and windows of your home and use insect repellants when you go outdoors. As we enter the early fall season we are prone to have tropical rainfall events that can create ideal mosquito breeding conditions. Be vigilant in preventing standing water from accumulating around your house and keep your doors and windows tight.