Last week a controversy surfaced regarding a July 24 article in USA Today, “Bugs like it hot: Record heat kicks bugs into high gear,” by Doyle Rice. Rice’s article implied that the intense heat experienced this summer has caused increases in populations of several insect pests, including grasshoppers, crickets and mosquitoes. Last week, two researchers from Purdue University challenged that theory in their own article, “Do bugs really like it hot?” and indicated that in the Midwest, the drought has actually reduced the numbers of mosquitoes, although the high heat has made it difficult to enjoy what they say is virtually a mosquito-free summer.
Members of a school IPM listserv began adding their own observations to the debate, and because the issue of mosquitoes and West Nile virus are applicable to the general public, I thought I would repeat the debate in today’s blog post and add my own observations of what’s going on in some of the southeastern states in terms of mosquitoes.
Dr. Linn David Haramis of the Illinois Department of Public Health counters the last statement made in the Purdue article that people are not being bitten by mosquitoes in the evening because the dry weather has decreased the number of mosquitoes. “In the Midwest, this statement is true if one is referring to “floodwater mosquitoes” (such as Aedes vexans) that appear after heavy rains. Additionally, floodwater mosquitoes are very rarely infected with West Nile virus because they do not feed on birds. Unfortunately, the statement in yellow highlighting above is not true when one refers to the northern house mosquito (Culex pipiens), the vector of West Nile virus. Because house mosquito larvae develop in stagnant street catch basins (storm drains) and similar locations they are present during droughts. The house mosquito is a stealthy biter and it is not as noticeable as the swarms of floodwater mosquitoes we see during rainy summers. Even if it does not look like there are a lot of mosquitoes out people need to use insect repellent in areas where WNV has been active. And that is many states this summer, see:
‘West Nile virus disease cases up this year: Take steps to protect yourself and your family. The Centers for Disease Control and Prevention is urging people to take steps to prevent West Nile virus infections. Outbreaks of West Nile virus disease occur each summer in the United States. This year, some areas of the country are experiencing earlier and greater activity.’
Dr. Jody Gangloff-Kaufmann with the NY State IPM Program says, “And in the Northeast where drought conditions are mild at best, the mosquito populations are absolutely out of control, along with increasing discoveries of WNV-positive pools of mosquitoes.”
In North Carolina, we have not experienced much drought. In fact, earlier this summer, the City of Raleigh policymakers lifted the permanent water restrictions because we were having so much rain. In my own backyard, I have a plethora of mosquitoes, but I also have a lot of shade (good shelter for insects). Personally I haven’t experienced more of an onslaught of mosquitoes than what I remember from last summer (which was also hot but very dry). But I’m not an entomologist, so I’m going to refer you to some people and publications with more expertise than I have.
Last year I did a blog post about how drought affects insect populations (http://ipmsouth.com/2011/06/10/does-drought-contribute-to-pest-problems/) that summarized what some of the scientific literature states about how droughts relate to insect populations. Last year, however, most of the country was experiencing a drought during the middle of summer. This year, weather patterns differ greatly depending on where you live. In most of the Southeast, rain has been abundant. In Arkansas, some of the state is wet and some areas are so dry that trees are already turning color. In Texas and the Southwest, residents would love for the Southeast to send them a few drops of the rain blessing the Southeast because crops are dying, fires are happening and severe watering restrictions are already in effect.
The best advice I can give homeowners is to follow your state’s recommendations for reducing mosquito populations in your yard. During a drought, most people water their lawns and gardens, and any small pool of water—whether it’s in your children’s Frisbee or a bird bath—is a great breeding ground for mosquitoes. So watch for places in your yard where puddles may occur after you’ve used a hose or run the sprinklers. Mosquitoes don’t care whether the water is from a well or rain.
I have also seen reports of increased flea activity this year, but this seems to be due to resistance of some of the common topical products. Some experts are recommending oral medications, so ask your vet if he or she has heard reports of high flea infestations and what to do to protect your pet.
Ultimately, the best advice I can give is, if you read a news report of massive insect population explosions, find your state’s University Extension website and see if it has news of similar populations. Extension agents usually do insect counts in most counties and are not interested in selling products, so the information they give you is most likely more accurate than that you may see in the news.