Due to record rainfall, the city's mosquito population is expected to explode this summer and authorities are gearing up keep the blood-sucking critters in check.
Mosquito traps placed throughout the city have already yielded high numbers, said David Henley, superintendent of the East Middlesex Mosquito Control Project, a Waltham agency.
"With the amount of rain that we've had, I'm concerned there's going to be a lot of mosquito activity that will continue into early August," he said. "At that point, it will depend on how much rain we get in the future to sustain the population."
The battle is joined tonight.
Truck-mounted aerosol sprayers will be spreading an insecticide today between dusk and 11:30 p.m. throughout Waltham.
Areas to be sprayed include Trapelo Road, Marlborough Road, Forest Street, Temple Road, Sheffield Road, Hardy Pond Road, Lake Street and Candlewood Drive.
In addition, spraying is planned for areas near Bacon Street between Plympton Road and Totten Pond Road, areas off Beaver Street between Lexington Street and Valley View Lane and streets in the vicinity of Curve Street, Pond End Road and Stanley Road.
Henley has been on top of the situation.
On July 6, he checked a trap near Hardy Pond, another at Marlborough Street near Beaver Brook and a third at a marsh near Kendall Park.
"All three traps were relatively high. All three traps got over 300 mosquitoes, which is a lot," he said. "The last time we sprayed in Waltham was in June, it was just a trap on Bacon Street, which was high. This time they were all high and primarily at least two of the traps had mostly floodwater mosquitoes, which would have come from the rain."
Since July 1 the city has had 3.67 inches of rain according to a gauge, Henley said.
"I think we're a little over our normal amount for July and June was a very rainy month," he said. "Between the two months in our rain gauge, we've had over eight inches of rain over a six-week period. That's pretty significant."
Henley said the traps consist of a three-inch fan that draws mosquitoes into a bag.
Another type of mosquito develops in a marsh near Kendall Park every year, independent of rainfall, Henley said.
"It's the one species we can't control in the larval stage, whereas the floodwater mosquitoes we can spray. But, there's so much rainfall that the wetlands are constantly full and producing a lot of mosquitoes right now."
Henley said there have not been any reports of any Waltham residents contracting West Nile virus or eastern equine encephalitis yet, but it's early in the season for the mosquito carrying-diseases.
"It's really August and September that's the prime risk period," he said.
Henley said eastern equine encephalitis is more of a concern during rainy summers.
"Because the species that spreads that virus develops in cedar swamps, it needs a long period of wet weather to sort of develop large populations," he said. "Usually in this area, the cedar swamps dry up during the summer."
The closest cedar swamps are in Bedford, Sudbury and Wakefield, but mosquitoes migrate, according to Henley.
The agency uses a spray formula containing the sumithrin, which is classified as slightly toxic by the state's Department of Environmental Protection.
"Because we are trying to control something with the body weight of a mosquito, we can use it in low amounts," he said. "It doesn't present a health hazard to people. It tends to be a little more toxic to insects than it would be to people, that's why it's a popular pesticide to use."
Henley said with any pesticide, people should minimize exposure. If residents see a spray truck approaching, they are advised to go indoors for a few minutes while the spray dissipates. Residents are also asked to close any windows facing the street.
According to Henley, mosquitoes start developing in wetlands around April 1. The spring floodwater mosquitoes are common to Waltham and emerge between mid and late May.
Another group of mosquitoes common to Waltham are summer floodwater mosquitoes. They usually emerge between June and mid-September, Henley said. Henley said there's also a species of marsh mosquitoes common to the city.
"Right now, our major concern is with the summer floodwater species," he said. "That population is starting to reach high numbers. I'm expecting they'll continue to emerge for the next week or so."
Henley said the culex mosquitoes, known as a bird-biting species, is also found in the city.
"They are the ones that develop in water-holding containers and they are the vectors of West Nile virus," he said. "People need to help in the controlling of them."
Henley said Waltham residents could help control the culex population by emptying objects that collect rainwater. He also said residents should treat their pools with a commonly sold pesticide to kill the mosquito larvae.
Information on the East Middlesex Mosquito Control Project's spray schedule is available at 781-893-5759 and at http://sudbury.ma.us/services/health/emmcp.
If spraying is postponed, it will be rescheduled for July 20.
If residents have any questions related to spraying or any questions on mosquitoes, contact the East Middlesex Mosquito Control Project at 781-899-5730.
Jeff Gilbride can be reached at 781-398-8005 or at jgilbrid@cnc.com.
