ADDISON COUNTY — An unusually wet, hot and humid summer has been miserable for humans but a veritable utopia for mosquitoes, which have been multiplying in vast numbers in many areas of Addison County.
“This is going to be one of the worst (mosquito) years we’ve had in a while,” state Entomologist Alan Graham said on Thursday.
“They have been very abundant, because of the rain.”
Steady, soaking rains have created an ideal habitat for many of the 45 different species of mosquitos that call Vermont home, Graham said, particularly those that originate in waterlogged floodplains.
“We are seeing some species that come out only when the water is really high,” he said. So thousands of acres of wetlands and agricultural fields have become breeding spots for the pesky insects.
Graham has been collecting thousands of specimens from traps in the state’s ongoing effort to track mosquito-borne diseases like Easter equine encephalitis and West Nile virus. A specimen recently caught in the Leicester area was confirmed to be a carrier of West Nile Virus.
What’s making this year’s bumper crop of bugs seem even worse is that it comes after a very mild 2012 mosquito season, Graham noted. Whereas Graham is finding up to 4,000 specimens of one mosquito breed in a single trap this year, he was finding only 25 to 30 in traps last year.
Representatives of the state’s three organized mosquito districts — all of which involve Addison County towns — echoed Graham’s observations, but with an additional wrinkle. They said they are seeing large numbers of mosquitoes in spite of the fact that the regular water samples taken within the districts’ waterways are not yielding the large numbers of larvae one would expect to see during a banner bug year. The mosquito districts conduct drops of larvicide in an effort to stamp out mosquitoes before they hatch and begin biting.
“We’re doing constant surveillance of larvae,” said Gary Meffe, chairman of the Brandon-Leicester-Salisbury-Goshen (BLSG) Insect Control District. “But we have seen low larval numbers in recent weeks.”
This, of course, flies in the face of the large numbers of adult mosquitoes flying around the area. Meffe theorized these mosquitoes might be coming from pockets of woodland — and not floodplains — spots that are more isolated and therefore tougher to treat with larvicide.
Meffe said many breeds of mosquitoes prefer moisture in “pulses,” as opposed to substantial and consistent rainfall.
“The constant rainfall is less conducive to (generating) mosquitoes,” he said.
Each of the three districts has access to $140,000 in state funds for the purchase of larvicide. That larvicide is dropped by a small plane owned and operated by the Lemon Fair Insect Control District (LFICD), which comprises the towns of Bridport and Cornwall. The LFICD also provides larvicide drops for the state’s third insect control district — the town of Weybridge.
So while the BLSG has only received a handful of larvae drops this season, the war on adults is in high gear. The BLSG is the only mosquito district in the state that sprays adulticide in areas where heavy activity is reported. The district has paid staff that use trucks and equipment to disperse the adulticide. The BLSG budget for the spraying comes in large part through annual contributions from the member-towns, including $27,746 from Brandon, $14,177 each from Leicester and Salisbury, and $9,174 from Goshen.
“I think we will get through this year, but it will be slim going forward,” Meffe said of the adulticide budget.
David Dodge is chairman of the LFICD board. He echoed Meffe’s reports about the relative paucity of mosquito larvae.
“With all the rain we’ve had, we expected to see a lot more larvae in the Lemon Fair area,” he said. “Amazingly, in spite of the rain, we have not had anywhere near the hatches we would have expected.”
But he added: “The mosquitoes are definitely out there. Exactly where they are coming from, we are not sure.”
To test for larvae, district workers and volunteers dip a white cup attached to the end of a stick into standing water. Dodge explains larvae have to be found at certain levels to warrant a larvicide drop. That threshold has been defined as a series of 10 mosquito dips (10 paces apart) with each producing and average of 50 larvae.
“We are looking at that minimum threshold to decide whether it’s still appropriate,” Dodge said. “The state has expressed a willingness to change it.”
Dodge said on Thursday that there had not been a larvicide drop in the LFICD since late May.
Consequently, the LFICD still has around three pallets of larvicide on hand at the Middlebury State Airport, ready to drop when and if the larvae levels spike.
In the meantime, people are being encouraged to eliminate standing water — such as in old tire or buckets — from their property, in order to reduce mosquito breeding habitat.
“It’s been a strange season,” Dodge said, adding the mosquito threat will remain until the first frost of the year.
Reporter John Flowers is at firstname.lastname@example.org.