The mosquitoes this summer have hit all-time highs and have been a real deterrent to being outside. Mosquito population trends for the summer have reached four times the number from last year. Visit the Iowa State University medical entomology lab mosquito surveillance website at http://mosquito.ent.iastate.edu/browse_county.php for more information.
"It is too late in the season for homeowner mosquito management actions to have much effect," said Laura Jesse, Plant and Insect Diagnostic clinician. "Eliminating all possible water sources – buckets, tires, bird baths, and other objects that hold water that the mosquitoes could use for their development may reduce the number produced on your property, but not those blowing in the wind from outside your property lines."
Floodwater mosquitoes (the most common biters) have no respect for property lines and easily can fly several miles from where they developed, according to Jesse. That's why the most effective mosquito management programs are those that involve an entire community or encompass a large area.
Personal protection remains the most practical way of contending with mosquitoes for the remainder of the year. Avoid the areas and times of day when mosquitoes are most active if you can, and wear long, heavy-knitted clothing. Apply mosquito repellents sparingly but thoroughly prior to going outside and wash thoroughly when you return inside.
The CDC suggests that you use any of several EPA-registered products that have been shown to provide reasonably long-lasting protection. For most people, a low-concentration product will be sufficient for short intervals out-of-doors. Those working outside longer can benefit from a higher concentration of active ingredient, or repeated applications as needed. EPA-registered products contain one of the following active ingredients: DEET, Picaridin, Oil of Lemon Eucalyptus or IR3535.
Consumer Reports magazine, July 2010, reviewed mosquito repellents and found that, "most of the tested products will do the job if you're going to be outside for only a couple of hours."
Also listen to a Consumer Reports podcast about the OFF Clip-On Repellent. Their conclusion was that the clip-on, fan-powered repellent did not work very well at keeping mosquitoes away from test subjects wearing the device in an enclosed cage of mosquitoes. Consumer Reports recommends that you choose a topical repellent for better results.
Giant numbers and giant mosquitoes
In addition to having an incredibly large number of mosquitoes in Iowa this year, extension entomologists also have had more questions and inquiries that start out, "I just saw the biggest mosquito of my life!"
“The very large mosquitoes that bite viciously are one of our 'usual' species found in Iowa,” said Donald Lewis, extension entomologist. “However, this year is different in that the population seems to be larger than normal.” The extra-large mosquitoes are in a genus called Psorophora. There is no customary common name for these mosquitoes, though some references use the term "gallinipper" or "gallinipper mosquito" for Psorophora mosquitoes.
Psorophora mosquitoes are a floodwater species. The females lay eggs on moist soil and the eggs hatch when covered with water from floods or temporary pools and impoundments. The larvae grow very quickly to the adult stage. Some of the Psorophora mosquito larvae are predacious; that is, they eat the larvae of other mosquitoes sharing the temporary pool. There can be several generations of Psorophora each summer depending on rainfall. In the fall of the year, the last eggs laid for the season remain dormant and wait for floods the following year. Some references claim the eggs can lay dormant for a long time and hatch years later.
Of the 14 species of Psorophora in North America, the one common in Iowa is Psorophora ciliata, a large mosquito with noticeably banded legs, pale stripes on the side of the dark thorax, and stiff, erect hairs along the legs. Females of Psorophora ciliata are vicious biters and prefer to feed on mammals. They will bite during both the day and night and are able to bite through heavy clothing.
“There is nothing special for the control of Psorophora mosquitoes,” Lewis said. “The usual homeowner/gardener actions of eliminating breeding sites such as bird baths, plugged rain gutters and old tires may help reduce some kinds of mosquitoes, but not Psrophora that are breeding in flooded fields. Personal repellents remain the best defense against biting.”