The common house fly is one species of filth flies coming under renewed focus as a vector of disease agents that can contaminate products in food plants.
Photo: Orkin Commercial Services
Zero tolerance may be the goal in insect and rodent remediation in food plants, but a priority list can be useful when deploying limited resources to combat an ongoing concern.
Thanks to the good folks at FDA, such a list exists. Created two years ago, FDA’s Dirty 22 is a guidance document that identifies the cockroaches, ants, rodents and flies that are critters non gratae in and around production and storage facilities. The species were flagged by FDA field labs because of their links to foodborne diseases.
Given their grazing habits and hairy bodies, filth flies are particularly adept at contaminating food with pathogens. In fact, the majority of the species are flies, a subgroup that could be described as the Filthy 12.
Feces and rotting organic material are breeding grounds and food sources for filth flies, a category that includes house flies and blow flies. DNA evidence implicated house flies in an E. coli O157:H7 outbreak at a Japanese day care center, and highly toxic methomyl pesticide proved inadequate in controlling the flies that descended on the victims of a Korean Airlines crash in 1997. Ten days later, “many bodies had been almost entirely consumed by maggots before they could be recovered,” according to a technical guide from the Armed Forces Pest Management Board.
“Flies have been neglected,” acknowledges Patricia Hottel, technical director at McCloud Services in South Elgin, Ill. “They are such a familiar pest, we sometimes don’t give them the attention they deserve in preventing the spread of disease.”
Cockroaches raise more fear and loathing than filth flies do, “but flies are a much bigger disease-transmitter than cockroaches,” seconds Ron Harrison, director of technical services at Orkin Commercial Services, Atlanta. He lauds the FDA guidance for raising awareness among processing professionals of the food safety danger they pose.
A good offense on the outside of a plant is the best defense against flies inside the facility, and researchers are developing new baits and traps to bolster exclusion strategies. An example of the latter is the Stealth fly station. Entomologists at Ecolab found that female flies in particular are drawn to dark, reflective surfaces, so they designed a trap that frames such a surface with a pesticide-laced border. In a demonstration involving 1,500 flies, the station achieved a kill rate of 85 percent within 50 minutes. Combining the station with a light trap tripled the mortality rate.
Filth flies are exemplars of Charles Darwin’s theory of evolution, leveraging their short maturation cycles to quickly adapt to and resist pesticides. To ensure interventions remain effective, pest control experts recommend rotating baits rather than relying on tried and (up to a point) true remedies.
Light traps, along with rigorous cleaning and sanitizing, are the best defense once filth flies have entered a food or beverage production facility.
Photo: McCloud Services
Two new baits reached the market in the past year: Alpine pressurized fly bait from BASF, with the active ingredient dinotefuran, and Zyrox, a granular bait with cyantraniliprole from Syngenta. They join Maxforce Fly Spot as recent additions to the anti-fly arsenal.
Besides countering flies’ adaptability, the new baits provide some flexibility in how and where they are used. Fly Spot, for example, is for indoor-use only. However, that’s not a green light for applying it in areas where food is processed or handled. Label directions limit applications to office areas and other spaces outside processing and storage areas, points out Chelle Hartzer, product manager-technical services at Industrial Fumigant Co., Lenexa, Kan. “Very few pesticides can be used inside. It’s usually a contamination issue.”
Some indoor pesticides can be applied in employee break rooms, a sometimes overlooked breeding ground. That’s where you’ll find one of Hartzer’s pet peeves. “I hate vending machines,” she says. “They never get moved, they never get washed underneath, and the compressor coils are a great heat source for breeding.”
What lurks below
Small filth flies include fruit flies, phorid flies and drain flies, and drains are a prime breeding area. Few chemical interventions exist, and those available are ineffectual against the flies’ eggs and larvae, observes Judy Black, vice president-technical services at Charlotte, N.C.-based Steritech. As a result, “two days later, the problem is just as bad,” she says.
Regular cleaning and sanitizing is the best defense. Foam is a more effective pesticide delivery medium in drains than liquid, but pesticide treatment is redundant if cleaning removes biofilm that supports both flies and pathogenic bacteria.
Drain inserts are a more effective defense. Originally designed to prevent sewer gases from entering the building, drain inserts also seal out flies and cockroaches, another pest that often gains entry through drains, particularly after heavy rains.
Trap Guard from ProVent Systems Inc. is a popular choice among pest-management professionals. The insert’s elastomer tail curls up and seals off the orifice unless there is downward pressure from wastewater, whether it’s a trickle or a torrent. However, weekly cleaning still is recommended.
“Most of the (small) flies are not attracted to light traps,” notes Black. “If you’re talking nontoxic intervention, you’re talking about cleaning and sanitizing.” That includes breeding areas beyond the drain. And regardless if the flies are large or small, “keep them out in the first place,” she advises. “Positive air pressure, screens on windows and doors that are closed” are the fundamentals of fly exclusion.
Loading docks are particularly vulnerable points of entry. A number of dock-door sealing systems designed with food and beverage plants in mind have come into the market in recent years, among them the Xcluder system from Global Material Technologies Inc., Buffalo Grove, Ill.
“If flying insects are coming in through dock plates, Xcluder should stop them, but we make no claims,” says David Colbert, vice president. “The dock area usually is the biggest entry point for rodents. Dock plates take a beating, and the brush seals on the side will never keep a rodent out.”
Colbert’s firm is a 110-year-old manufacturer of steel wool, and many manufacturers stuff steel wool or copper mesh around dock doors as a stopgap. Xcluder is a more permanent solution: Course stainless steel fibers and polyester fill fabric are stuffed in bumpers that rodents can’t chew through. The system usually is welded into place, though a more economical version that’s manually positioned was introduced this year.
An even more button-downed solution is the Eclipse dock shelter from Rite-Hite Corp., Milwaukee. When combined with the firm’s PitMaster sealing system, the shelter “seals the dock up as tightly as possible on all four sides,” according to Mary Blaser, marketing director. A no-hook version introduced this year accommodates liftgate trailers and trailers with doors that open inside the building in a drive-through application.
Energy savings on refrigerated docks help recoup Eclipse’s cost, but the four-sided protection also enhances pest control. “Auditors and inspectors want to see complete darkness at the dock,” says Blaser. “Even our best earlier shelters couldn’t deliver complete darkness.”
No door system is infallible, of course. The pounding they take from lift trucks and trailers virtually guarantees alignment problems will surface over time. New interior baits are few and far between, though suppliers have demonstrated considerable creativity in recent years by mixing and matching various active ingredients to create new solutions.
“Even when there are bumpers and guards on at least three sides of a dock door, trailers may not fit perfectly, particularly at the base,” points out McCloud’s Hottel, “and once that door opens, flying insects can find easy access.”
Adds Orkin’s Harrison, “Flies aren’t a problem, they’re a symptom of a problem.” The Filthy 12 list has helped raise awareness about some of the nastiest pests in terms of spreading disease, but unless the root cause of their presence in a food plant is addressed, killing the adults only provides temporary relief.