Nancy Edmonds Hanson
hansonnanc@gmail.com

Ben Prather predicts that, despite his annual campaign, you’ll be swatting more mosquitoes by the weekend.
“These are the worst possible conditions for fighting mosquitoes,” the director of Cass County Vector Control said this week. “Hot, humid, frequent rain leaving lots of water in low-lying areas – it’s about as bad as I can ever recall.”
Prather has headed the West Fargo-based regional mosquito control program since 2009. Originally charged with combating Cass County’s biting bug population, his unit has taken on Moorhead’s defenses since 2015, when the city downsized its own bug-killing operation. Moorhead pays about $100,000 per year for its share of Cass County Vector Control’s $1.2 million budget, equal to or slightly less than when it ran its own annual campaigns. It’s funded by a monthly fee of about $1.06 per household.
Ben and his summertime squad of 40 provide intense ongoing coverage for an area extending from three miles west of Horace and West Fargo to six miles north and south of Fargo, plus within the Moorhead city limits. That encompasses leftover floodwater and low spots along 56 miles on each bank of the twisting, tortuous Red River, as well as miscellaneous bug breeding hot spots all over town – kiddie pools and watering cans, so-called “water features” in golf courses and neighborhoods, rain-catching containers of every kind, construction sites and empty lots, all often awash with lingering liquid from the latest rains.
While lawn-mowers and families eating in back yards may find it hard to believe, Ben reports that 2019’s seasonal infestation is considerably lower than at the highest points in the 10 years he’s spent in vector control. (“Vectors” are biting insects or ticks that transfer a disease or parasite from one creature to another.)
“How bad are the mosquitoes? It’s always a matter of perception,” the Fargo native points out. His group monitors the local population from early May through freeze-up with 38 traps placed strategically throughout the metro area. “We’ve been average a little more than 100 since June 10,” he says, comparing it with past annual highs of more than 300. But, he says, when they’re keeping you from enjoying summer fun, those are only statistics: “Once you go from bad to worse, it doesn’t really matter whether you’re getting one bite per minute versus two or three.”
Part of why this year seems particularly pesky is the contrast between the dry years just past and a far rainier stretch of summer. “Drought is good in terms of keeping the mosquitoes down,” he explains. Mosquitoes lay their eggs in water; when stagnant pools are in short supply, the larval hatch is minimized. But those eggs survive, awaiting more conducive conditions. This year has filled that bill, from spring flooding that left many areas swampy to the frequent heavy rains, both here and to the south, which have swollen the river again and left behind perfect pools for coddling the tiny young mosquito hatchlings.
His prediction of perils to come is based on the timing of the most recent downpours. Adult mosquitoes emerge seven to 14 days after eggs hatch. Coupled with delays in ground and aerial fogging, which require nearly calm conditions in the right range of temperatures, and you have the potential for a big itch.
Ben, a pre-health sciences graduate of the University of North Dakota, confesses he never took even one class in entomology. “Biochemistry was more my thing,” he says. Nevertheless, he’s amassed a wealth of understanding of the little buggers in the most practical way possible: working hard to wipe them out. As a student, he spent summers working with Cass County Vector Control’s ATV-riding patrols. Armed with sprayers and tanks of the least toxic chemicals approved for larvicide, he and his coworkers scoured the lowlands and woods looking for pools full of developing larvae.
After a stint in engineering in the Twin Cities, he worked for Metropolitan Mosquito Control for two and one-half years, learning the ins and outs of “every nasty, remote, bug-infested spot” in the metro area. He returned to Fargo to head Cass County’s ongoing war on mosquitoes ten years ago.
While trucks fogging residential areas with micro-droplets of permethrin may be the most visible measure by the mosquito warriors, along with low-flying aerial sprayers, Ben says 90% of his agency’s battles target larvae. They look like small hairy worms, less than a quarter-inch long,with hard round heads, soft bodies, and segmented abdomens with siphon tubes at their tip.
Starting in early spring, his crews spend long hours stalking their prey, which resemble quarter-inch hairy worms. Then they spray the nontoxic organic larvicide BTI. The naturally occurring bacterium, found in soils, contains spores that produce toxins that specifically target and only affect the larvae of the mosquito, blackfly and fungus gnat. Once ingested, it’s activated by their alkaline digestive system. It causes virtually no harm to other creatures, from frogs to humans, most of whom have highly acidic digestion.
The mosquito fighters use a different application for fogging. Micro-droplets of permethrin must make direct contact to kill flying adults. Permethrin is a based on a natural chemical derived from chrysanthemum flowers, which use it to repel their own insect predators. “It’s similar to nicotine. Humans, mammals, vertebrates and some invertebrates are able to process small amounts without problems,” Ben says. Dosage is monitored closely, with custom equipment designed to emit ultra-low volume droplets. Each application – just three so far this summer – is calculated to deliver less than one gram per acre. “You can never say with certainty that anything is 100% nontoxic, but we balance the least toxicity with the most beneficial outcome,” Ben notes. Permethrin is approved for treating humans’ head lice and scabies, flea and tick treatments and cattle wash, and it’s a frequent ingredient in yard fogging products.
Twelve to 20 mosquito species – of 3,000 documented around the globe – inhabit the region. Some, like the ones the Canadians call “big buffalo mosquitoes,” don’t bother humans. Six to eight have developed a taste for Homo sapiens, however, each with its own preferences, from floodwaters to stagnant pools. “Aedes dorsalis is the worst. I hate them,” Ben says. They hang around river banks and storm catchments. Unlike most of their cousins, who prefer to dine from dusk into the evening, Ben’s least favorites feed throughout the day. “We’re seeing huge numbers this year.”
Most species are merely annoying. One that Vector Control takes even more seriously, though, is Culex tarsalis, the mosquitoes that have been implicated in spreading western equine encephalitis. The viral infection can be deadly. Back in 1975, they prompted a full-fledged emergency response when 27 Red River Valley residents were diagnosed; four died. Hundreds of horses also tested positive. Members of the Minnesota National Guard were deployed here to spray to reduce the threat.
That remains a possibility, Ben says, but that none has been identified in the Red River Valley in recent years. His office is vigilant. Traps are emptied each evening. Then staffers count the number of each species, as well as the proportion who are female. They’re the biting kind, requiring a blood meal to produce eggs. The males? They’re just cruising, looking for girls.
Years of trapping and counting have revealed some local mysteries. One is the inexplicable crowd collected in the trap just south of Concordia’s Jake Christiansen Stadium. Though it’s well away from the riverbanks or any obvious hatching hotspot, it consistently ranks at the top of the nightly census. “We don’t know why. We’ve even gone door to door in the neighborhood looking for stagnant pools or containers, and we haven’t been able to find anything,” Ben reports.
No matter how thorough their stalking of larvae, Ben and his troops recognize that mosquitoes are an inevitable part of the local summer. “Even if we eliminated every single larva in our own area, we know some people are still going to feel the bite,” he admits. “After all … mosquitoes can fly.”