Mosquito Heaven

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It has to be a vector control specialist’s nightmare. Just as the waters are receding and people are beginning the long task of recovering from Hurricane Harvey, the mosquitoes set in. And it’s not only the current egg-laying bunch that are producing offspring; eggs laid previously can lie dormant—as long as three years for some species—and can hatch and develop when conditions are right.

Houston, in the southernmost part of the US, is warm enough to provide a comfortable habitat for the Aedes aegypti mosquito, which carries the Zika virus and other diseases like yellow fever and dengue. The floods and the still-standing water in many places have just made it an even more enticing spot for them.

So far this year, Harris County, where Houston is located, has had five human cases of Zika, although as this article in The Scientist notes, the people affected might have contracted it while traveling to places where it is more widespread than in the US. There have also been two cases of West Nile virus, which is carried primarily by mosquitoes of the genus Culex. Officials in Texas acknowledge that most of the mosquitoes appearing in the wake of the flooding are unlikely to carry disease and are mainly a nuisance, but there are definitely a lot more of them than normal. As the article notes, mosquito populations are generally monitored in two ways: one, by measuring how many mosquitoes are caught in a network of traps located throughout the county; and two, through the “landing-rate count,” or the number of mosquitoes that land on a person in one minute. In the areas with lots of standing water and vegetation, the article reports, “counts have been more than 100 per minute, double the levels that would normally be considered high.”

As a precaution, Air Force planes are spraying insecticide across several Texas counties, including Harris County. Aerial delivery is not the normal practice here; spraying is usually done by truck, and then only in areas where a disease-carrying mosquito has been trapped. (The trucks are out in force, too, spraying at night in the worst affected places.) Florida residents protested en masse last year when aerial spraying took place, fearing the effects of the insecticide more than the threat from the mosquitoes.

Here is a link to an article we’ve mentioned several times, particularly since the Zika virus came onto the world’s radar, about the nexus between stormwater management and mosquito control efforts. SW_bug_web

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