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Bite Boom: Rains Spur Biggest Mosquito Population in Three Decades

Mosquito This is the kind of buzz you don’t want.

In addition to stirring up water pollution, the recent heavy rains across the Chesapeake Bay region also triggered a near-record mosquito population boom.

Mike Cantwell, chief of the mosquito control section of the Maryland Department of Agriculture, said mosquito populations on Maryland’s western shore are the highest he’s seen in his 30 years of studying and trying to control the insects.

“Normally, at this time of the year, with the cooling temperatures, we are seeing a decline in mosquito populations,” Cantwell said.  “But due to the large amount of rainfall that we’ve had, we’ve actually had an increase at this time of the year. And so far the weather isn’t getting cold enough, fast enough to dramatically reduce these mosquito populations, or their biting.”

In sections of Baltimore County, monitoring of the insects has revealed mosquito populations that are  about three times higher than normal, Cantwell said.  In low-lying sections of Maryland’s Eastern Shore, the numbers are even higher.  Recent counts of mosquitoes in parts of Dorchester County have been over 100 per minute, compared to fewer than 12 per minute last year.

To deal with the mosquito population boom, the state agency has increased is spraying of insecticides by hand, trucks and from airplanes.  Last year, MDA had suspended its normal spraying activity by this late in the season. But because of all the rain, the state agency will be spraying at least another two weeks, Cantwell said.

About 1.5 million acres will be sprayed with insecticides to control mosquitoes this year in Maryland, compared to 200,000 or 300,000 acres in some past years.  The insecticides being used are  Bacillus thuringiensis israelensis, a naturally produced bacterial toxin; Bacillus sphaericus;  and methoprene (Altosid), a synthetically produced insect growth regulator, according to the Maryland Department of Agriculture.

If you have questions about the state's mosquito control program, click here.

Have any readers out there seen any other increases or decreases in insect populations in your neighborhood after the rain?

I know I’ve seen huge populations of dragonflies in Baltimore, which could be related to rains over the summer and fall making wetlands more fertile as breeding grounds. Some people have suggested that invasive stink bugs and gypsy moths can be suppressed by wet weather. 

Any experiences or insights to share?

By Tom Pelton

Chesapeake Bay Foundation

(Photo from iStockphoto)

Comments

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what species are you finding?

I live in Deale, MD on Herring Bay. Since the two tropical storms in August and steady precipitation since, the mosquito population has significantly increased in my backyard. My backyard has not been able to dry out.

I use rosemary oil to repel mosquitoes.

About 1.5 million acres will be sprayed with insecticides to control mosquitoes this year in Maryland, compared to 200,000 or 300,000 acres in some past years.

I know I’ve seen huge populations of dragonflies in Baltimore, which could be related to rains over the summer and fall making wetlands more fertile as breeding grounds

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