[Annual Fly Control Issue] Small Flies = Big Problem

While ants have received much press as the No. 1 pest for pest management professionals the last few years, another class of pests has been steadily moving up the ladder of concern. Described by some as the "cockroach of today" and the most common problem pest in commercial accounts, small flies have been getting pest management professionals’ attention from coast to coast. It is now commonplace for patrons of restaurants and bars to be bothered by fruit flies. While perhaps not viewed as "disturbing" as cockroaches, small flies represent at best a nuisance and at worst a public health hazard. They frequent unsanitary areas with decaying organic matter and pick up bacteria and fungus that they can spread to food.

The reasons for the increase are likely related to the way we now control cockroaches. Before baiting became the mainstay for roach control (and in an era of less regulation), pest management professionals used residual sprays to control roaches, which likely resulted in what could be termed "collateral control" of other likely pests as well, including small flies (and ants for that matter). "We used to spray down monthly with residuals and rotate chemicals to combat resistance," says Tim Runyon of SWAT Pest Management, Evansville, Ind., "but now we use baits most of the time. It’s no surprise we’re seeing big increases in fruit flies in the chain restaurants we service."

Secondly, before baits, roach control required more effort to be successful, particularly in the area of sanitation. However, with the remarkable effectiveness of baits, proper sanitation was no longer crucial, leading some in the industry to conclude that good sanitation is no longer necessary for roach control in most cases. In addition, high employee turnover in the food-service industry is also thought to contribute to decreasing sanitation standards. In the absence of broad-spectrum residuals and proper sanitation, commercial accounts, particularly bars and restaurants, are rife with potential breeding sites for small flies, thus the recent increase in problems is not surprising.

SMALL FLY SPECIES. The most common small flies encountered in commercial accounts are fruit (or vinegar) flies, phorid (or humped back) flies and drain (or moth) flies. While some traits are similar among the different flies, many are not. It is critical that pest management professionals know which of the flies they are confronting in a particular account.

Fruit flies (Drosophila spp.) are about 1/8-inch long and have large red eyes and tan to brown bodies. Fruit flies are attracted to the early stages of food decay, namely fermentation of sugars and starches caused by yeast, which is a food source for the larvae. They are not particularly attracted to light except for briefly after their emergence as adults, and are less likely to be found in insect light traps (ILTs). The author was recently visiting a nursing home kitchen and noted that although the ILT contained numerous phorid flies, the major problem in the account was clearly fruit flies. While fruit flies may breed in drains, it is common for them to breed in any crack or crevice that contains food and moisture or on pieces of food that may have fallen into inaccessible areas.

More recently, another species of fruit fly, called the "dark-eyed fruit fly," has been appearing in problem accounts. This fly is larger and darker in appearance and has dark red — vs. bright red — eyes. It tends to favor more advanced stages of decay of protein based materials, rather than yeast-driven fermentation. While primarily identified as a problem in the Northeast U.S., technical staff at Omaha, Neb.-based Presto-X-Company have recently reported what appear to be dark-eyed fruit flies in an account, so the problem is likely more widespread.

Phorid flies (Family Phoridae) are similar in size to fruit flies but generally darker in appearance, with a distinctively arched thorax and small, dark eyes. Phorids are highly adaptable and can breed in any moist, organic matter, including garbage, drains and mops. These flies have a particular penchant for decaying bodies and are thus often found in morgues. Sub-slab drain leaks can accommodate extremely large numbers of phorid flies underground that may continuously enter the structure through cracks in the slab or other openings. The only solution to this problem is to fix the leak.

Drain or moth flies (Family Psychodidae) have a smaller body than fruit flies and have large wings covered in long hairs, giving them a moth-like appearance. Drain flies most commonly breed in the bio-films that form in drains and in sewage treatment plants. The adults are strongly attracted to light.

MANAGEMENT STRATEGIES. Since small fly problems originate mainly indoors, they tend to be a problem year round and in all climates. Occurring most often in food service accounts and bars, control strategies must take into account regulatory constraints for food-handling establishments. As discussed, small flies can breed in almost any area where food and moisture come together, including cracks and crevices in floors and baseboards, drains, bars areas, food-prep equipment of all types and drink-dispensing machines. Sanitation considerations must be communicated to accounts and documented. In addition, preventive measures, such as sealing up cracks and crevices and relocating processing machinery to areas that better facilitate cleaning, can be either performed by the technician or recommended in writing to the account.

Modern control strategies involve control of adults, breeding site elimination and in some cases use of insect growth regulators to prevent reproductive maturity. Trapping accomplishes three things: namely knock down of adults (the ac-count’s principal complaint), capture of invaders before they establish and breed (new flies can come in every day with produce and supplies), and monitoring to pinpoint breeding areas and to detect problems early. Larger traps consist typically of one-way hanging cup type traps with a liquid attractant that also serves to immobilize the flies. Smaller traps typically consist of glueboards to capture the insects, either used alone or inside a plastic station. Gel attractants are available for use on glueboards.

The newer attractants that contain proteins, as well as fermented material, will be more widely effective in that they will attract phorid and drain flies, and dark-eyed fruit flies, in addition to the common red-eyed fruit fly. Hanging cup plastic traps or glueboards used in plastic stations can be converted to "killing stations" by wiping the plastic surfaces with microencapsulated residual insecticide diluted per the label. A common dish-washing liquid dispenser works well for this purpose and allows more precise delivery vs. spraying. Flies that land on the station will pick up the residual and die, even if they don’t get trapped.

"We’ve had good success knocking down adults with killing stations," says Runyon, "and the dish soap sponge applicator works great." While the killing station can be used effectively without the glueboard, the glueboard has value as a monitor. Traps can be placed under bars, near garbage and in other areas near potential sources. The size of trap used should be determined by the location and customer visibility. Hanging cup traps will typically attract from farther away than glueboards, by virtue of the fact that they contain a greater amount of attractant. Liquid attractant may also be used in an insect light trap to help bring in fruit flies since they aren’t strongly attracted to light normally. The attractant can be put in a small condiment cup and placed inside the light trap. Cotton balls can be put in the cup to prevent spillage and to slow evaporation.

The latest techniques for breeding site elimination involve the use of biological products. Biological products contain microbes and/or enzymes that digest organic matter. They are often formulated with chemical cleaning agents, such as degreasers, but do not contain pesticides. Biological products for drain cleaning have been marketed for at least 10 years, but only recently have they begun to be used specifically for small fly control.

The first biologicals marketed in the pest control industry were not surprisingly drain treatment products, since they existed in other markets. However, as discussed, small flies often do not breed in drains, so only drain treatment will not always solve the problem. Subsequently, cleaning and mopping products containing biological agents have been developed. These products are typically sold to the account, rather than applied by the technician. The rationale is that when the cleaning staff mops, they are pushing water and food particles into cracks and crevices that then ferment and create breeding sites. By adding biologicals to the mop water, these agents also get into the cracks, crevices and drains, and digest the organic matter.

The latest biological products in pest management professionals’ arsenal are foaming products. These products are applied using a hand foamer, wherein the technician foams potential problem areas, including cracks, crevices, drains and nooks and crannies in equipment, etc. These products are fast-acting and the foam provides longer contact time than liquid.

"We started our fly control program two years ago and have used drain cleaners, microbials, and enzymes with good success," says Phil Kreer of APM Companies, Elkton, Md. "Crack and crevice foaming is a great way to get at the places restaurants don’t clean." Due to the short life cycle of small flies, biologicals often provide quicker results than might be expected.

Lastly, insect growth regulators can be used in drains and in certain crack and crevice treatments per the label, to prevent maturation and reproduction. Since insect growth regulators are classified as pesticides, their use is regulated by the label and by state pesticide laws.

CONCLUSION. Rather than considering small flies to be a problem, pest management professionals should actively work to include, rather than exclude, them from their commercial contracts and profit from them.

"We started our fly control program with the specific intent to increase revenue from existing accounts," Kreer says. "We’re pretty excited about the results."

It is important, though, that technicians be trained in the modern control methods. "We’ve actively made an effort to train our techs in small fly control," says Harold Leyse of Minneapolis, Minn.-based Adam’s Pest Control. "It’s a growing area and we feel it can be a competitive advantage."

The author is president of Rockwell Laboratories Inc., Minneapolis, Minn. She can be reached at cspragrins@pctonline.com.