Released June 9, 2011
LINCOLN, Neb. — As areas along the Missouri and Platte rivers are hit by floods, the number of mosquitoes is expected to increase.
But it's too early to predict whether there will be an increase in the risk of mosquito-transmitted West Nile virus, because it depends on how long the floodwater stays around, said Roberto Cortinas, assistant professor in entomology and veterinary and biomedical sciences at the University of Nebraska-Lincoln.
"The thing with mosquitoes is we have two types of mosquitoes," Cortinas said. "We have floodwater mosquitoes and standing water mosquitoes."
Floodwater mosquitoes such as the Aedes vexans, also commonly known as the inland floodwater mosquito, will lay eggs in dry areas in anticipation of flooding or rain, Cortinas explained.
These eggs may survive a few years without water and hatch into mosquito larvae when water pools in the area. Mosquito larvae develop into pupae and then emerge from the water when they become adult mosquitoes.
Because of this year's flooding, the number of Aedes vexans likely will increase. These mosquitoes transmit dog heartworm, which infects animals, primarily dogs, but it is easily preventable, Cortinas said.
"Luckily, the Aedes vexans mosquitoes are not the key player in the spread of the West Nile virus," Cortinas said.
The West Nile virus is the most important mosquito-transmitted disease in North America. In 2010, 39 cases of West Nile were reported in Nebraska with two of those leading to death.
The mosquito that spreads West Nile virus is Culex tarsalis, a standing water mosquito. This kind of mosquito prefers to lay eggs in existing, stagnant water sources, such as water in a paper cup or old tires.
So for the Culex tarsalis mosquito population to increase substantially – thus increasing the risk of West Nile virus transmission – the floodwater would have to remain pooled for a few weeks, Cortinas explained.
In prior years, floodwater in Nebraska has drained quite quickly after floods, but that doesn't mean things can't change this year, Cortinas said.
"We can't anticipate how long the flooding is going to persist, so that's the concern," Cortinas said.
In the meantime, people can protect themselves against West Nile virus by controlling mosquito populations around their area and preventing mosquito bites.
Barb Ogg, UNL Extension educator in Lancaster County, said long-term mosquito control starts with people eliminating mosquito breeding grounds instead of just spraying insecticide.
"If they're going to spray their yard, it'll be effective for maybe a day or two," she said.
Anything in the yard that collects water, such as flower pots, cans and old tires, should be emptied. Dump out the bird bath at least twice a week, Ogg said, and check gutters to make sure they are not clogged.
For ponds or flooded areas, briquets or granules of the bacteria Bacillus thuringiensis israelensis (Bti) can be used to kill mosquito larvae, Ogg said, but it won't harm birds, fish mammals and other organisms.
People can avoid getting bitten by mosquitoes by making sure window and door screens are in good condition, and by remaining indoors during dawn and dusk, which is when mosquitoes are most active.
When venturing outside, it's advisable to wear long-sleeved clothing and long pants. Light-colored clothing seems to attract fewer mosquitoes than dark-colored clothing, Cortinas said.
Mosquito repellents help prevent mosquito bites, too. Ogg said the U.S. Centers for Disease Control and Prevention recommends three kinds of mosquito repellents:
- DEET is the most common chemical used in insect repellents. DEET is effective, lasts up to eight hours depending on the concentration and is considered "the gold standard" for mosquito repellents, Ogg said. However, many people don't like DEET because it has an oily feeling and odor.
- Picaridin is as effective as DEET but it isn't as long-lasting. However, it is not greasy and doesn't have an odor, so some people prefer Picaridin over DEET.
- Oil of lemon eucalyptus (PMD) is extracted from the lemon eucalyptus plant. People like it because it's a natural substance, Ogg said, but it lasts for a shorter period of time than DEET or Picaridin of the same concentration, so it needs to be re-applied more frequently.
For more tips on controlling mosquitoes around the home, visit UNL NebGuide Residential Mosquito Control.
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University of Nebraska, http://ianrnews.unl.edu/static/1106091.shtml
Sources: Barb Ogg, (402) 441-7180
Roberto Cortinas, (402) 472-6052
Writer: Sandi Alswager Karstens, (402) 472-3030
