Mosquito spraying deemed successful Insecticide applications on the evenings of June 23 and 24 reduced Vermillion's mosquito population significantly, resulting in trap counts 59 to 92 percent lower than pre-spray totals.
Vermillion's northwest residential streets, plagued with high mosquito numbers all summer, saw a 69 percent drop in mosquitoes. Before spraying, Prentis Park showed mid-range numbers, but a worrisome percentage of those mosquitoes were Culex Tarsalis, a variety likely to transmit West Nile.
Spraying reduced Prentis' mosquito population by 61 percent, bringing nightly trap catches to fewer than a dozen mosquitoes.
Despite such promising numbers, mosquitoes will still be around to bite and bother Vermillion residents. Spraying kills only adult mosquitoes who contact the insecticidal fog, leaving many mosquitoes to continue breeding and biting. Spraying does not affect larva emerging from water or adults migrating in from the countryside � two major factors in the rebound of post-spray mosquito populations.
Some hotspots will require additional treatment. For instance, spraying at the city recycling center reduced the trap count from 594 mosquitoes the night before spraying to just 211 after spraying. By the next night, however, the count had rebounded to 330.
In an attempt to interrupt breeding cycles, the area around the recycling center will receive targeted applications of larvicide and additional spray the week of June 28.
A well-designed, consistently monitored trapping system remains key to fighting mosquitoes. Without data from traps, it is impossible to determine the effectiveness of larviciding, or even more importantly, of spraying.
"Without traps, spraying is like trying to shoot in the dark. You can't tell if you need to spray, where you need to spray, or even if your spray was effective," said Todd Schultz, Vermillion's mosquito control specialist. "When the state opened up grant funding to combat West Nile, they told us that surveillance had to be the first priority in our mosquito control programs."
Parks & Recreation Director David Nelson identified trap sites around the city when he applied for state funding last winter, and Schultz spent the last few days of May and the first week of June placing the traps at the designated sites and creating a system for collecting and analyzing data.
"The data from our trapping program has been incredibly valuable. It's given Dave and I the tools we need to make decisions about larviciding and spraying. Also, with the help of April Borders at the county Extension office, we are able to know what types of mosquitoes we are catching and if they are the type likely to carry West Nile," Schultz said.