GREENVILLE — Long at a disadvantage in the ceaseless war against mosquitoes and the diseases they bear, the Mississippi Delta is about to catch a break.
A new pesticide has recently been approved by the State of Mississippi for use in the Delta, where, years ago, organophosphate-based pesticides were heavily applied to counter the cotton-infesting boll weevil.
That liberal use of that class of pesticide inadvertently lent mosquitoes a resistance to what elsewhere has proved to be the most effective weapon against them: a chemical known as Dibrom.
Vector Disease Control International, which has a $280,000-a-year contract with the City of Greenville, last year conducted field trials of the new product, DeltaGard, which is manufactured by a division of Bayer CropScience LP, and “the results were phenomenal,” Kris New, Vector’s regional director, who is based in Greenville, said last week.
“(DeltaGard) has a 99 percent effectiveness,” said Jeff North, a consultant with Sanford, Florida-based Adapco Inc., a mosquito-abatement pesticide supplier that distributes the product.
“Two weeks ago, Mississippi approved its use, and it should be in the rotation around mid-June.”
The similarly effective Dibrom continues to be used effectively outside the Delta, where mosquitoes have not developed a resistance to organophosphates.
DeltaGard also is deemed environmentally friendly, degrading within roughly half an hour and, so, posing little risk to beneficial insects such as honeybees, which are key to crop pollination, New said.
“You want knockdown, and then for the product to degrade,” North said.
Vector, founded in 1992 in Little Rock, Arkansas, and now operating in 16 states, has its national operational headquarters in Greenville, and its aviation fleet is headquartered at Greenville Mid-Delta Airport.
The vector of the company’s name refers to the mosquito, the culprit responsible for transmitting disease, including, most notably in the Delta, the West Nile virus.
Mosquitoes acquire the virus by feeding on the blood of birds carrying West Nile and then infect human beings in the same way; they are the vector, or disease transmitter.
Vector last week began spraying in Washington County for mosquitoes, two weeks earlier than in 2014. Still, the annual battle began well before then.
“In March, we began putting out larvicide in standing water and setting out our traps,” New said. “We began spraying on May 4, much earlier than last year, when the mosquito season got off to a late start. Our first spray night last year was May 22.”
That late start was due to an unusually wet early spring, and 2014 also was a relatively innocuous mosquito season.
“Last summer was not all that hot, and we had frequent rains, and that kept the populations down,” New said.
While 60 or so mosquito species are found in Mississippi, the Delta is home to only six or seven species, most of which New described as merely “nuisance mosquitoes; they bite, they’re annoying, but they don’t really carry a threat of disease.”
One species that has proved far more of a threat — culex quinquefasciatus, better known as the Southern house mosquito — carries the West Nile virus and tends to show up in large numbers later in the breeding season.
West Nile tends to be more prevalent in years that are both hot and dry. Birds and mosquitoes then tend to flock to what water they can find, and drawn together, mosquitoes feed on the birds, some of which carry the virus, and then transmit it to human beings, said New, who graduated for Mississippi State University in 2001 with a degree in agricultural engineering.
Vector annually sets out its traps in nine zones throughout the city.
“They show us what species are present, and they let us know when to time our spray-truck schedules,” New said. “Some species are daytime fliers; culex is all night. We check them Mondays and Wednesdays every week.
“If we see a whole lot of male mosquitoes, which hatch 12 to 14 hours before the females and don’t bite, they don’t need a blood meal, we know that in half a day, you’re going to have a whole lot of females, and we need to be aggressive going after them.”
Vector also works closely with Greenville’s Public Works Department to deal with drainage constrictions that provide prime breeding grounds for mosquitoes, he said.
The mosquito season in the Delta typically runs about six months and “typically tapers down toward the end of October,” New said, “but we usually get service requests into November.”
Such requests are available free of charge for property owners “as part of our contract with the city,” he said.
“If you’re having an event, we’ll come out to your property and spray for free. Last year, we probably did 900 applications on private property. The year before, I think it was more than 1,000.”