Purdue News
Purdue News
"Of primary concern are nuisance biting mosquitoes," said Ralph Williams, Purdue University Cooperative Extension Service entomologist. "These are the types of mosquitoes that occur as a result of accumulated water from heavy rains."
Williams said these nuisance biters are aggressive, but aren't a concern in disease transmission. Disease-vectoring mosquitoes aren't as aggressive and breed more in water allowed to stagnate in containers and other places. Williams said there are more than 3,000 different kinds of mosquitoes worldwide, and more than 50 of those are found in Indiana. Only a few are nuisance biters.
"Only the female bites," Williams said. "She draws blood to use as a protein source for her eggs. Both the male and female mosquitoes feed primarily on nectar and plant juices."
The first line of defense against becoming a mosquito-bite victim, he said, is avoidance. Eliminating breeding grounds and hiding places is a good start.
"All mosquitoes breed in standing water," Williams said. "Female mosquitoes lay their eggs on water or in low-lying places where water is likely to accumulate. Some species lay their eggs in marshes, ditches and flood plains. Others will make their homes in gutters, old tires and birdbaths."
Draining water from these potential breeding sites before mosquitoes can move in, and eliminating containers that can hold water, will make these spots less appealing for mosquitoes. Also, loosening soil in flower pots will ensure that water penetrates instead of forming a stagnant pool.
"Adult mosquitoes tend to hide in heavy vegetation during the day," Williams said, and removing tall grass and weeds will force them to hide elsewhere. To keep them outdoors, make sure screens on windows, doors and porches are in good repair. Williams said gaps around windows and doors can be filled with weather-stripping to deter mosquitoes.
As for repellents, citronella candles are limited in their effectiveness because air movement can easily disperse the citronella. Physical repellents, such as bug "zappers" and ultrasonic devices, have not been proven to be helpful, Williams said.
Personal repellents are helpful, but some are more effective than others. Williams suggested looking for an EPA-registered mosquito repellent to keep the pests at bay. He said the EPA registration number will be printed on the front of the label. Citronella-based products are popular because citronella is a natural ingredient, but citronella dissipates within a few minutes and has not been shown to be very effective. DEET-based products are the best and longest-lasting mosquito repellents on the market, according to experts, but some consumers are wary. Williams and his colleague Jonathan Neal stress that DEET should be fine if consumers strictly adhere to label directions.
"Repellents with other ingredients are not as effective as those with DEET," said Neal, who is an insecticide toxicologist at Purdue. "DEET has been used a long, long time with minimal effects."
He said low concentrations of DEET -- 6 percent to 10 percent -- can even be used safely on children if applied sparingly and according to label directions. However, he cautioned that it should not be used on infants and children under the age of 2.
"In cases where children have become ill from DEET, concentrated amounts were applied, the whole body was covered, and it was applied often," he said. "With children and mosquito repellents, it's generally recommended that a parent apply the repellent and not let children apply it themselves so the application can be better regulated. The mouth, eyes, scratches and wounds should be avoided so the product does not enter the body. It's also recommended that it not be applied to kids' hands, since they often put their hands in their mouths."
Neal said some people may be sensitive to a repellent; they should immediately rinse off the product and get medical attention. In any case, repellents should be washed off after returning indoors.
Neal and Williams recommend staying indoors at dawn and dusk, when mosquitoes are hungriest and most active. If you must be outdoors then, they suggest wearing long-sleeved shirts and long pants with enough thickness to prevent mosquitoes from reaching the skin. Williams said mosquitoes are attracted to dark colors, so light-colored clothing is best. Some repellents that contain permethrin and can be applied only to clothing will help keep mosquitoes away.
Alas, though, sometimes all of your best efforts are for naught and you get a bite. What to do then? Col. David Goetz, a pediatric allergist stationed with the 59th Medical Wing at Lackland Air Force Base, San Antonio, Texas, said symptomatic treatment is about the best you can do. He said the bump and itch are a response to mosquito saliva injected into the skin. Chemicals in the saliva include an anticoagulant that brings blood to the skin's surface so the mosquito can feed on it. The bump you get is a physiological response to the chemicals; the itch may be a histamine response.
"There's a wide variation of responsiveness," he said. "The skin will slowly get back to normal on its own." He recommended plain calamine lotion, as well as topical hydrocortisone, for bite treatment.
Sources: Ralph Williams, (765) 494-4560; e-mail, ralph_williams@entm.purdue.edu
Jonathan Neal, (765) 494-4594; e-mail, jonathan_neal@entm.purdue.edu
Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu
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Writer: Andrea McCann, (765) 494-8406; e-mail, mccann@aes.purdue.edu