[Pest Management] Phorid, Fruit or Drain

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The flies measure in at less than 1/8 of an inch, and you can differentiate them by the color of their eyes (fruit fly), the hump of their back (phorid fly), and their fuzzy appearance (drain fly).

Sure, you say, at 1/8 inch I’m supposed to be able to notice all that?

True, you will probably need at least a magnifying glass — or the eyes of a seasoned pest management professional but however the distinction is made, it is important to do so. Each fly is different not only in appearance, but also in feeding preferences, breeding sites and habits — thus making proper identification critical for effective control and elimination.

IDENTIFICATION. 
Phorid flies — Also called humpbacked fly, referring to its primary characteristic, adult phorid flies are yellowish-brown and tiny (1/16- to 1/8-inch long) with an arched thorax (“hump back”), a small head with rather large eyes, and long, large legs. Male phorids are much smaller than females, so there may seem to be two different species. Larvae are dirty white in color and less then 1/16-inch long. Almost cylindrical, they are slightly flattened, and tapered at the front; the light-brown pupae is a bit longer, boat-shaped and slightly translucent. Eggs are very small (1/32 inch) and opaque-white.

Fruit flies — Also called vinegar or pomace, the adults are about 1/8- to 1/5-inch long, dull brownish-yellow to brownish-black in color with some species having red eyes. The head and thorax are tan, while the abdomen is black and gray underneath. Males and females are about the same size. Eggs are pearly white with two to four threadlike tubes; larvae are about 1/10- to 1/5-inch long, cream-colored, legless and eyeless. Tapering to a point at the head, the larvae have an extended stalk-like breathing tube at the tail. The brown, seedlike pupae are about 1/8-inch long with two hornlike stalks at one end.

Drain flies — Because of its tendency to hold its large wings roof-like over its furry body when at rest, this fly is also called a moth fly. The dark or grayish adults are 1/5- to 1/6-inch long with hairy body and wings. The antennae are long with 13 segments and each has a “bulbous swelling” with a whorl of long hairs. The brown or cream-colored eggs are laid in irregular masses of 10 to 200. Wormlike larvae are about 3/8-inch long with both ends somewhat darker.

BREEDING.
Phorid flies — Phorid flies reproduce in moist areas where food and water are present — decaying organic matter, drains, garbage receptacles, food equipment, elevator pits, mop or broom heads, septic systems and overwatered plants. There is almost nothing this fly will not infest, and it travels far from its breeding site. So, it can be difficult to impossible to use the habits of adult phorids to locate their breeding site. Eggs usually are laid directly on the decaying material, about 20 at a time (40 eggs over a 12 hour period). Eggs hatch in 24 hours with the entire life cycle lasting about 25 days.

Fruit flies — Fruit flies reproduce in fresh fruits and vegetables, particularly those beginning to ferment. They are found in residues of beer, wine, liqueur, sour mop/broom heads, dish or mop water, and around baseboards and drains. Red-eyed fruit flies can be quite predictable in their breeding habits, as the female’s first choice is to lay its eggs on the substrate they developed in as larvae. The female will lay 500 to 2,000 eggs singly near the surface of moist, fermenting food material. Eggs hatch in 24 to 30 hours into tiny larvae that feed near the surface of fermenting food masses, with the entire life cycle completed in 8 to 15 days.

Drain flies — Drain flies reproduce in polluted, shallow water or highly moist organic solids, such as slimy or unused drains, backup, dirty garbage cans and even air conditioners. Eggs, which can hatch in 32 to 48 hours at 70° F, are laid in and on the moist media, and the life cycle can be completed in one to three weeks. Adults live about two weeks, with old ones dying and new ones emerging.

HABITS AND DAMAGE.
Phorid flies — Phorid flies move in a crawling-flying style, and are likely to crawl rapidly in a zig-zag manner on a surface. They may be seen running rapidly across windows, computer screens, tables, walls and plant foliage in short, jerky movements, appearing reluctant to fly. Phorid adults are resistant to varying humidity and seasonal temperature conditions, and are just as active in mid-summer as in mid-winter. Because the fly breeds and feeds in decaying matter, it can be a serious pest in food-processing plants, carrying the potential to transmit bacteria to food products.

Fruit flies — Fruit flies are strong fliers, but don’t tend to move far from their breeding site, especially if it remains humid. Newly emerged flies are attracted to light, and will land and rest in one spot for a while, though window sites are often too dry for them. Adults are attracted to yeast growth that causes fermentation. Populations may build up on boxes of cracked tomatoes in the field or on pallets at receiving stations of canneries.

Some species of fruit flies have been responsible for human intestinal myiasis, which is common among workers in grape vineyards.

Drain flies — Drain flies are weak fliers, and make irregular, hesitating flights covering only a few feet in short, jerky lines. They feed on flower nectar and polluted water, resting during the day in shaded or moist areas and are most active during the evening when they can be seen hovering around drains and sinks.

Adult drain flies can become so numerous indoors as to fall into food and accumulate around drains; outdoors they mar fresh paint and plug sewage filter beds (intakes and drains). Since these flies originate in filthy conditions, there is the possibility of human health disease transmission; inhaling fragments and dust of dead flies can cause bronchial asthma.

MANAGEMENT AND PREVENTION.
Phorid flies — The most important task in phorid fly management is to locate and eliminate the larval breeding sources. Carefully inspect facilities for concentrations of adult flies and decaying odors.

The flies are attracted to natural light and will fly erratically around lights at night. For monitoring, sticky traps with a yellow background will be most attractive, and these and insect light traps can be placed in several locations and monitored at one or two month intervals. For prevention:

• regularly and thoroughly clean drain pipes and traps. It often is best to remove the drain trap and use a snake in clogged drains to remove all gelatinous material, and bleach or commercial drain cleaning products may be poured into the drain pipes after a thorough cleaning by brush, carefully flushing with boiling water.
• use a dehumidifier or fan to eliminate or reduce unnecessary moisture or dampness and avoid accumulation of wet organic matter in roof or ground drainage sites.
• outside, use high-pressure sodium vapor lights, rather than mercury vapor lights, and place them away from doors and windows. Keep excessive vegetation (grasses, leaves) away from the foundation; dispose of dead rodents and old bird nests; clean garbage containers and seal (caulk) cracks and crevices to prevent entry sites.

Fruit flies — With fruit flies, it is best to concentrate on eliminating breeding and larval feeding sites, so sanitation is critical in successful control. Sometimes simply eliminating overripe fruit, fermenting foods, empty containers or dirty garbage cans will control these pests. For prevention:

• check garbage-laden drain water, clean gelatinous material in drain pipes and install 16-mesh screens, as these flies can pass through ordinary house fly screening.
• identify breeding sites by placing masking or clear plastic tape over drain openings overnight to detect and monitor fly emergence.
• because the flies are attracted to light, replace exterior mercury-vapor lamps with sodium-vapor lamps and set them away from entrances.

Drain flies — It takes persistent effort to eradicate a drain fly infestation. For management and prevention, concentrate on eliminating larval breeding sites from drains in floors, sinks, wash basins, and:

• identify breeding sites by placing masking or clear plastic tape over drain openings overnight to detect fly emergence.
• regularly and thoroughly clean drain pipes and traps. It is best to remove the drain trap and use a snake in clogged drains to remove all gelatinous material.Bleach or commercial drain cleaning products may be poured into the drain pipes after a thorough cleaning by brush, and then the pipes should be carefully flushed with boiling water.
• keep all garbage containers — indoor and out — clean and eliminate all standing water.
• outside the plant, inspect air conditioners, shallow stagnant pools of water and upwind sewage treatment facilities as adult flies will travel with the wind.

The author is staff editor of QA magazine.