[Pest Management] The Food Plant: a Fly Magnet

For control purposes and discussion, flying insects  generally are divided into two key groupings: large flies and small flies. But regardless of which group you are dealing with, the most critical first step is identification. “It is important to know which one you have,” said Cisse Spragins, President and CEO of Rockwell Labs Ltd.

LARGE FLIES. The most common pests of the large fly grouping are house flies and blow flies. Blow flies generally are larger than house flies and are a metallic blue, green or copper color. In urban areas, they sometimes can be more abundant that house flies.

These flies typically breed outside and become a problem during the warmer months. They tend to come into plants through entryways and other openings and are attracted by the warmth, light and smells. “When you open up your doors in a food plant, you’re going to get both those flies,” Spragins said. “The plant is going to be very attractive to them because they’ve got food there.”

Large flies are more likely to be a seasonal pest, increasing as the weather warms, and they are a problem because, as explained by Doug VanGundy, director of specialty product development for Wellmark International and board-certified entomologist, “they are mechanical vectors of Salmonella.” Because they will land on fecal matter then on food, large flies can spread a variety of other pathogens as well.

SMALL FLIES. The small flies, most commonly including fruit, drain and phorid flies, breed inside plants “in any build-up of organic material,” Spragins said, with drains as a very common problem area because of the biofilm which builds up and scum on which the larvae can feed. However, drains are not the only problem area, she cautioned. “They will find other areas where you have organic build-up,” such as in equipment cracks, standing water, etc.

The small flies are especially problematic because they are small, VanGundy said. “They can breed in just a little bit of organic matter.” Because of this, sanitation is critical to eliminating — and preventing — small fly problems.

In addition, because these flies have very short life cycles, you will accomplish very little by killing only the adults. Rather a program needs to be implemented to kill the eggs, larvae and adults and eliminate the sanitation problems which are enabling the flies to live. Characteristics of the small flies include:

• Fruit. Though a traditional identifier for fruit flies is their red eyes, the black-eyed fruit fly is actually becoming a bigger problem today, Spragins said. Fruit flies “are all about scum.” They feed on and breed in organic matter, thus sanitation is critical to the prevention of fruit fly infestation. “Just a little peach or pear somewhere stuck under equipment can breed a lot of flies in a little area,” VanGundy added. While fruit flies are not generally a seasonal pest, some plants can be more susceptible to them in the warmer weather, and, as the fruit fly’s name implies, plants which bring in a lot of fresh produce generally have the most issue with this fly. Once the flies are in your plant, any source of organic matter can provide a site for them to feed, breed and multiply.
• Drain. It may be self-evident that drain flies will often be found in drains; what may be less evident is the ease at which matter can build up in drains providing a habitat for these flies. Flour mills, for example, can have a great deal of problem because wash down of floors does not eliminate the build up on the sides of the drain; in fact, flour dust collection in this area is a key problem source. 
• Phorid. Phorid flies most commonly  are associated with structural issues, such as sub-slab leaks, which can lead to very expensive repair costs. They are attracted to decaying organic matter.

MANAGEMENT STRATEGIES. The specific management strategies used to control flies in food processing facilities are determined in large part by the target pest. What follows is a brief review of the common management strategies for both large flies and small flies.

Large flies. “A lot of traditional controls are addressed to house flies,” Spragins said. “But what you actually find more now are blow flies.” Thus it is critical to know which fly you have. While cultural controls will be applicable to both flies, if chemical control is being considered, it is imperative to ensure that it will attract the blow flies and is not targeted to just house flies, she said.

The best defense against large flies is physical barrier to their entry, VanGundy said, citing strategies such as air curtains or strips and traps at dock doors. The loading dock is a critical area for exclusion. “It’s a fly magnet,” he said. “Basically (plants) are producing food and that’s what (the flies) are after.”

External chemical controls can also help kill flies before they get a chance to enter your building, such as scatter bait applied by a professional at garbage shoots and grease pits. External garbage areas can be a big problem, Spragins affirmed, especially if it includes food waste. “That’s going to be extremely attractive, so that every fly in the neighborhood is going to show up for the party for that,” she said. And, if not stopped, the flies will then move indoors.

“Once (the flies) come inside, you are more limited as to what you can do,” she added, explaining that you can’t use product inside as freely as outside, thus insect light traps generally are used extensively inside plants. “The goal,” she said, “is to catch them as soon as possible.”

“Strategic placement of lighting is still an issue the food plants need to look at,” said David Gilbert, president of Gilbert Industries. Exterior lights should not be directed toward entryways or placed within 300 feet of an entryway, as these simply will attract flying insects into the plant. While lighting inside the plant can beautify such areas as administrative offices, it also can attract flying insects from the exterior. One solution Gilbert recommends is the placement of colored window film to diffuse the lighting attraction.

Small flies. If you see small flies in your plant, the first step is to capture samples for your pest control technician to identify, VanGundy said. But put them into a vial or jar, not taped onto paper, which will crush the insects and make them difficult to identify. “It’s important to know what species they are so you know where to target treatment,” he said.

Probably the most popular control for small flies is foaming, Spragins said. This can be applied to cracks, crevices and drains, and it will cling to the surface for longer control. The foam also can be “pushed through” the drain system and be helpful for infection control, she said. However chemical treatment will not get rid of the biofilm in drains. Rather you need to use microbials to digest and break it down.

Cleaning a plant with power spraying actually can increase your risk for small flies. “I often see that it is sanitation oriented,” she said. “A lot of times if they’re doing a lot of wash-down type of cleaning, they’re putting a lot of noise into the environment.” This “noise” actually helps insects, providing them with habitat. Spragins recommends that plants just be aware of this, look for areas in which it may be happening and then have these treated with a microbial.

In addition to the specific controls for large and small flies, your service technician should provide advice on exclusion, prevention and treatment specific to your plant. VanGundy recommends the plant have or find a good pest control company that is knowledgeable in the business. Because there is a whole host of specifications to work out, “the technician should work with the sanitarian to design a program for sanitation and maintenance of equipment,” he said. “The plant should work with the pest control company to come up with the best management plan they can. It is critical that they work together.” 

Lisa Lupo is staff editor of QA magazine.