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The Coos Bay World: Larvicide Mutes Mosquitoes


Officials say larvicide application is successfully squashing Bandon’s mosquito population.

Coos County commissioner John Sweet said this week that the larvicide Vector Disease Control International is applying to ponds within the Ni-les’tun Unit of the Bandon Marsh National Wildlife Refuge is working.

A fixed-wing aircraft applied Bacillus thuringiensis israelensis (Bti) to areas of concern on Sunday, according to the Vector Assessment and Control Committee’s website. The areas that couldn’t be reached by air were treated on foot Monday and Tuesday using gas-powered blowers.

The goal is to prevent the Aedes dorsalis larvae from maturing into the biting adults that swarmed the city last summer.

The next Bti application is expected following high tides on Monday and Tuesday.

“The U.S. Fish and Wildlife finally has admitted that they actually created this problem,” said Vector Assessment and Control Committee chair Roger Straus at the June 3 commissioners meeting. “That took awhile, as we all know. And they are working on cleaning up the problem.”

That clean-up will include eliminating pools in the marsh, he said, which is expected to begin in mid-July and finish by the end of September. USFWS has received several bids, and Sweet said they will be reviewed late this week or next week.

There was a fly-off of the adult Aedes dorsalis the first weekend in May, when temperatures rose. It occurred before the larvicide application permits were in place.

“Their life cycle, I believe, is four to six weeks, so the adults that flew off will eventually die off,” Straus said.

Commissioner Bob Main pointed out that larvicide is not being sprayed over the marsh; it’s applied in the form of pellets.

“Monitoring indicates the mosquito population is nowhere near where they were last year,” Sweet said. “The early hatch is dying off. It appears at this point that the system that’s being implemented is working, but we still have the most difficult time of the summer to come, so we’ll just hope that this continues.”

Bandon residents have expressed concerns that eliminating these areas of the marsh will cause the mosquitoes to breed on their property, though Straus said that won’t happen.

This species of mosquito only breeds in standing salt water, he said, so once those areas are eliminated, the problem should cease to exist.

Residents also said the county should have looked into options besides spraying to solve the problem: cutting grass, removing water sources, diking the marsh or draining the swamp.

Rob Taylor, of Bandon, blames the USFWS and said the county should not look to the agency that caused the problem to solve it.

While mosquito magnets have been provided to residents through the city of Bandon, Straus said they’re only a small, quick fix. The magnets cover one acre and they capture every mosquito species.

The committee is also working on providing bat houses through a USFWS grant.



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