How to keep mosquitoes at bay.
by Dr. Bennett Jordan, Copesan Director of Technical Support and Regulatory Compliance
No matter where a building resides in the country, mosquitoes are a part of a facility manager’s summer. But unlike other types of flies, these pesky insects are more than just a nuisance. Besides their bothersome buzzing and biting, which can make spending time outside unbearable, mosquitoes are a major public health risk because they can serve as vectors of numerous human diseases.
BEWARE THE BITING BUG
Mosquitoes are best known for the habits of the adult females, which must feed on blood before they can generate eggs. Their desire to produce offspring is so strong that they are willing to risk being swatted. Male mosquitoes, on the other hand, feed solely on nectar and plant juices; they never bite humans or animals.
Regardless of sex, adult mosquitoes are not easy to identify by sight. Most of the dozens of species found across Canada are an indistinguishable assortment of tans, browns and blacks. Size is typically not a diagnostic feature either. In fact, species-level identification is best performed by entomologists and often involves counting hairs or patches of scales, both of which may be lost during the mosquito’s life or post-mortem handling.
There is, however, a physical characteristic that differentiates male from female mosquitoes. Males have plumose or highly brush or feather-like antennae, while females have much more sparse antennae. Still, the easiest way to tell a mosquito’s sex is to see if it will bite.
THE DREAD OF DISEASE
Mosquitoes are, by a factor of thousands, more dangerous than any other group of animals on earth. Canadians have been spared from malaria, yellow fever, dengue fever and other prominent mosquito-borne diseases so these insects have been mostly regarded as a nuisance rather than a serious threat. While there are rare cases of encephalitis spread by mosquitoes, the public health focus locally intensified with the first human case of West Nile virus in 2002.
The explosion of the Zika virus in 2015, combined with its effects on pregnant women and babies, caused a state of panic worldwide and led many people to become extremely fearful of mosquitoes. Zika virus is primarily transmitted by the yellow fever mosquito but the Asian tiger mosquito may also be a competent vector. These mosquitoes are found in North America, though their range is limited to the southwestern, southern, southeastern, mid-Atlantic and lower Midwestern regions of the U.S. A small number of Asian tiger mosquitoes have been collected during surveillance in the Niagara region, but there is no evidence to suggest they are an established species.
The primary concern for Zika virus still comes from travel-related cases. In the last two years, there have been nearly 500 travel-related Zika cases associated with Canadians, and 5,000 travel-related cases involving U.S. citizens who have voyaged to regions where Zika is prevalent and were diagnosed after returning home.
FEAST OR FAMINE: WATER’S ROLE
Understanding mosquito control requires knowledge of the insect’s development. Mosquitoes have a complete metamorphosis with four life stages: egg, larva, pupa and adult. If conditions are ideal, the life cycle can be completed in less than two weeks. It’s easy to see how populations can explode when females can lay dozens to hundreds of eggs at a time. The first three life stages require water and only adults resemble what is thought of as a mosquito.
The most effective method of control is to reduce or alter the water that can be used as breeding habitat. The amount and type of water required varies by species. For some, called ‘container-breeders,’ larvae require very little water; less than half an inch is enough to develop normally. Facility managers should keep an eye out for empty pots, bottles, barrels, bird baths and other vessels that might hold water. If found, turn them over so water can’t collect and support mosquito development. Should containers need to be upright, empty them weekly to disrupt the mosquito life cycle.
There are also species that require lakes, marshes, flood water, seepage areas and other stagnant pools. In general, these breeding sites are harder to regulate and control through habitat modification so other methods may be necessary. Some mosquitoes will lay eggs above the water line or even in dried out water beds. Eggs will remain dormant until submerged in water, kick-starting their development.
There are two categories of chemical and biological mosquito control: larvicides and adulticides, depending on what stage of development is being targeted. Larvicides prevent mosquitoes from ever reaching adulthood by treating the water in which they develop. The primary advantage is mosquito larvae are confined, often at considerable densities, in one place. This means they can easily be killed with minimal applications of insecticide before they reach adulthood since mosquito larvae and pupae must remain at or near the water’s surface to breathe. The greatest disadvantage is that there are restrictions placed on treating bodies of water.
There are several types of mosquito larvicides, each of which kills larvae in different ways. One type of larvicide uses a naturally-occurring soil bacterium, Bacillus thuringiensis (often abbreviated Bt), which is formulated into liquids, briquettes, powders, pellets or granules. Once applied to water, the bacterium is ingested by the mosquito larvae and proteins are converted to toxins that destroy their gut. Other types of larvicides include growth regulators that prevent maturation into adulthood and a monomolecular film that prevents respiration at the water’s surface by larvae.
Killing adult mosquitoes presents a greater challenge because they can spread out over much greater distances and move three-dimensionally. When they aren’t active, mosquitoes often rest in shaded and protected areas. Localized treatments (those not applied aerially or over a large area) target these spots. Pest management professionals apply insecticides as fogs or mists, typically at very low volumes of insecticide, so ultrafine droplets can reach resting mosquitoes.
This article was originally published in the July 2017 issue of Facility Cleaning & Maintenance magazine.