Top 10 Facts You Should Know about Mosquito Control and Zika Virus Jerome Goddard, PhD
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There are many types of mosquitoes. There are at least 60 different species of mosquitoes occurring in the state of Mississippi.1 Only a few of them are significant pests of humans, while many others are quite obscure, being found in unique and limited habitats. For example, there are some species of mosquitoes that feed only on frogs2 and some that live only inside pitcher plants occurring along the coast.3 One of the common mistakes people make is thinking that all mosquitoes are the same and behave the same way.
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Different species of mosquitoes breed in different places. Mosquitoes can be roughly grouped into categories based upon their breeding sites. Many Aedes species breed in artificial containers around the house or holes in trees. Others, like the Anopheles, breed in permanent water such as swamps or lakes. The West Nile virus vector in Mississippi, Culex quinquefasciatus, prefers water with high organic matter content such as that in septic ditches and storm drains. Some of our worst biting mosquito species come from groups such as Psorophora and Aedes which breed in floodwaters or woodland pools after heavy rains.
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Not all mosquito species are vectors of disease agents like Zika virus. Interestingly, not all species of mosquitoes have the capability to pick up and later transmit disease agents, a concept called vector competence.4 There are lots of examples of this. In places with malaria, only Anopheles mosquitoes are the vectors despite the fact that there are many other mosquitoes in those areas. Also, after heavy spring rains, people get concerned about excessive mosquito biting from floodwater mosquitoes, but these mosquitoes are not carrying disease agents. The same is true for Zika; not all mosquitoes in Mississippi are able to transmit the virus to humans (see below).
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Only two species of mosquitoes in Mississippi are likely competent vectors of Zika virus. Zika virus is primarily transmitted by the yellow fever mosquito, Aedes aegypti and the Asian tiger mosquito, A. albopictus. Both species are very similar in appearance and habits. Aedes aegypti is a small black species with prominent white bands on its legs and a silver-white lyre-shaped figure on the upper side of its thorax (Figure 1). It breeds in artificial containers around buildings such as tires, cans, jars, flowerpots, and gutters, and usually bites during the morning or late afternoon. It may readily enter FIGURE 1. The primary mosquito vectors of Zika virus in Mississippi: A. houses and seem to prefer human blood meals (as opposed to Aedes aegypti, and B. Aedes albopictus. Note the difference in white animals), biting principally around the ankles or back of the neck. markings on the back (Figure courtesy Mississippi Department of Health). Interestingly, in many places in the U.S. where A. albopictus was accidentally introduced, this species has virtually disappeared, apparently being displaced. Aedes albopictus is widely distributed in the Asian region, the Hawaiian Islands, parts of Europe, and much of the Americas, including the southern U.S., where it was accidentally introduced in 1986.5,6 This species is similar in appearance to A. aegypti having a black body and silver-white markings, with the major difference between the two being that A. albopictus has a single, silver-white stripe down the center of the dorsum of the thorax (instead of the lyre-shaped marking) (Figure 1). It also breeds in artificial containers such as cans, gutters, jars, tires, flowerpots, etc., and seem especially fond of discarded tires. This is an aggressive daytime-biting mosquito, often landing and biting immediately.
178 VOL. 57 • NO. 6 • 2016