Well, I don't think you can be sure you're not drawing infected female mosquitoes to the culture pools. But, you can be obsessive with managing the culture pools and being sure to capture all larvae. I live in northern Delaware and have been tailoring my culture practices to match the increased West Nile problem. So how do you accomplish this? I have three 1 gallon tupperware containers that I rotate through culturuing. These are setup with declor water and some yucky melon rinds - the mosquitoes just love it. I monitor the tubs each day until I start seeing egg rafts. As soon as egg rafts are observed I start the countdown to 10 days. (Mosquito larvae stay in the water 4 to 14 days depending on the genus/species. Through studying the typical larvae I got early this summer I judged that the ones I deal with tend to stay in the water for 10 days. Higher temperatures can also cause larvae to develop faster.)