Texans will see mosquito population explosion

Anticipating a significant increase in the state’s mosquito population, Texas A&M AgriLife Extension Service entomologists are offering tips on how Texans can help slow mosquito breeding in backyards and protect from being bitten.

“Mosquito populations are booming throughout the state and will likely not go away anytime soon after all our rains and flooding,” said Dr. Mike Merchant, AgriLife Extension urban entomologist in Dallas. “Not all of the mosquitoes swarming us right now are likely to carry disease, but West Nile virus-infected mosquitoes are beginning to show up in traps.”

The Asian tiger mosquito shown here is one of the two mosquito species known to commonly transmit the chikungunya virus. The other is the closely related yellow fever mosquito. Both species are found in Texas. (Texas A&M AgriLife Extension Service photo by Dr. Mike Merchant)

Texas Department of State Health Services recently announced the first 2015 case of West Nile virus in the state, and Dallas County Health and Human Services just issued a health advisory reporting its first positive mosquito pool of the year.

Merchant added that chikungunya, another disease transmitted by mosquitoes, is on the radar of U.S. and state health officials as a growing concern. He said the virus is regularly brought into the U.S. by travelers, but as yet a human-to-mosquito-to-human cycle has not developed in Texas.

“This could change, however, as it did last year in Florida where a handful of cases occurred among Floridians who had not traveled to the Caribbean,” Merchant said. “The principal mosquito vectors of chikungunya include the Asian tiger mosquito, Aedes albopictus, and its close relative, the yellow fever mosquito, Aedes aegypti. Chikungunya frequently comes with a very bad headache, joint pain, rash and fever. There is no treatment for or vaccine to protect from this disease.”

For more information about where mosquitoes can breed, and how to identify Aedes and other mosquitoes, Merchant suggested going to AgriLife Extension’s Mosquito Safari website, http://mosquitosafari.tamu.edu.

Humans are not the only ones to suffer from mosquito-borne diseases, AgriLife Extension experts noted.

“Mosquitoes can also be vectors for dog heartworm,” said Dr. Sonja Swiger, AgriLife Extension livestock/veterinary entomologist in Stephenville.

According to Swiger, an infected mosquito can pass tiny heartworm parasites on to any uninfected dog it bites. Heartworm causes lasting damage to heart, lungs and arteries, and can affect the dog’s quality and length of life. In addition, horses are susceptible to several encephalitis diseases, including West Nile virus, and should be vaccinated every year.

Swiger said that to control mosquitoes effectively and economically, everyone should understand their basic life cycle and be familiar with the important mosquito types. According to Swiger, mosquitoes can be divided into two groups based on where they lay their eggs. For example, floodwater mosquitoes lay eggs on the ground in low spots, and these eggs hatch when it rains and the low area fills with water.

“With the unusually high May rainfall, these mosquitoes are common now and likely to remain so during the duration of the rain,” she said. “Floodwater mosquitoes are good fliers and can travel many miles from their breeding sites in temporary pools, roadsides and low lying areas.”

She noted there is little people can do on their own property to protect themselves from floodwater mosquitoes, other than stay indoors or wear repellent.

“We have more control over other mosquitoes that breed in containers and live closer to town,” Swiger said. “Container breeding mosquitoes include some of the most significant species that may negatively affect human health, including the common house mosquito.”

The entomologists referred to what they called “the four D’s” as a general means for people to help manage mosquitoes and protect against bites. These are:

— Dusk/Dawn – Avoid being outside when mosquitoes are searching for a blood meal, which is usually in the early morning hours and just before the sun goes down. While some species are daytime biters, most prefer to feed at dusk and dawn.

— Drain – Empty standing water from “containers” around your home and work areas, such as buckets, wheelbarrows, kiddie pools, toys, dog bowls, water troughs, tires, bottles, etc. Make improvements that allow standing water to run off following rains.

— Dress – If out during mosquito feeding hours, wear long sleeves and pants in plain colors. Avoid attracting them by wearing excessive amounts of perform or aftershave.

— Defend – Any time you go outside for an extended period of time, wear an insect repellent.

Dr. Charles Allen, AgriLife Extension entomology program leader in San Angelo, said mowing tall weeds and grass can help eliminate some mosquito resting areas.

“When mosquito populations are high, labeled contact insecticides can be used to knock down adults,” he said. “For greatest effectiveness, sprays should be directed to shady mosquito resting areas. In addition, insecticide-based misting systems can be effective short-term, but repeated applications can cause insecticide resistance or be harmful to non-target insects and may result in loss of control. These systems are most likely to be effective if timers are set to spray when mosquitoes are most active.”

Allen said there are also techniques that can help control larval stage of mosquitoes in water.

“Mosquito dunks containing insect growth regulators or Bti, the mosquito larva’s bacterial natural enemy, can be used in water that cannot be dumped or drained to reduce mosquito populations,” he said.

Products that apply a surface film or oil on the water can also be used to reduce larval mosquito and pupal populations by preventing them from getting air through their breathing tubes, he said. The use of films or oils should be limited to locations without any other organisms, since it will prevent oxygen to the non-target organisms as well.

According to Merchant, insect repellent is still the best overall defense against those “less savory insect and mite biters.”

“I always suggest people keep a bottle or can of repellent just outside their doorway to remind them to spray exposed skin, even if they plan to be outside just a short while,” he said. “Keeping repellent in your car is a very good idea too.”

The entomologists agreed that repellents with DEET remain the gold standard for protection.

“DEET has some of the best persistence. However, there are good alternatives to DEET if you aren’t going to be outside very long,” Merchant said. “The natural repellent, oil of lemon eucalyptus, is a good alternative to DEET for those who prefer an organic product. The most important thing is to find a repellent that works for you and to use it.”

Merchant periodically posts news updates on mosquito activity on his City Bugs website, http://citybugs.tamu.edu. He also has developed four short videos on different aspects of mosquito control that can be found at http://bit.ly/1F8cZkg.