An overturned water cap has enough water for a female mosquito to lay 300 eggs, with roughly 50 emerging as mature insects.

Now imagine clogged gutters, bird baths and discarded tires, all breeding grounds for those pesky little blood suckers, who can ruin a night around the campfire.

That's why Columbus Public Health is asking residents to follow three simple rules: tip, turn, toss -- all intended to get rid of any standing water.

"If you get something like a wheelbarrow full of water, you're taking hundreds, if not thousands, of mosquitoes," said Ryan Younge, manager of the vector-control program for Columbus Public Health.

The city has been trapping and two places -- in northeast Columbus and in south Linden -- have tested positive for West Nile virus.

Most people who become infected after being bitten by a mosquito carrying the virus do not have any symptoms, Younge said.

About one in five who become infected develop a fever with other symptoms, such as a headache, body aches and joint pain, he said. The most at risk are small children, the elderly, the immunocompromised and pregnant women, he said.

Columbus Public Health mobilizes in areas where West Nile virus and abnormally large populations of mosquitoes are found in traps, Younge said.

That includes spraying an insecticide called permethrin in two forms -- a fogging spray and an agitator, which causes many resting mosquitoes to fly into the lethal spray, he said.

Officials also drop larvicide pellets into 800 sites of standing water and other areas brought to the attention of Columbus Public Health, he said. Those who seem to be experiencing a large amount of mosquito activity can call the city's neighborhood hotline at 614-645-3111.

The eradication efforts will continue until the first hard freeze, likely in November, kills off the mosquitoes.

"We do not have set schedule (for spraying)," Younge said. "It is all based on that surveillance and trap testing for the disease."

In the meantime, residents can protect themselves by wearing pants and long-sleeve shirts at dusk and dawn, when mosquitoes are most active, and wear DEET-based insect repellent, he said.

The Franklin Soil and Water Conservation District also has a training course for those who purchase rain barrels, which can be an effective breeding ground for mosquitoes, said Erika Rowland, administrative specialist for the agency.

Part of the instruction calls for keeping a lid on the barrels and applying larvicide, which can be purchased from hardware stores and other retailers, Rowland said.

"Proper setup and maintenance of the rain barrel should keep mosquitoes out," she said.