Phorid Flies
Overview
Phorid flies (Diptera: Phoridae) are considered among diverse and successful groups of insects. There are approximately 4,000 known species of phorid flies distributed worldwide. In pest the control industry, a few species of phorid flies can be a nuisance in medical centers, food processing plants, restaurants, homes, and wherever decaying plant materials are present. Anyhow, these little bugs can be beneficial as multiple species of Pseudacteon phorid flies are currently known to be biological control agents of red imported fire ants.
Identification
To the untrained eyes, phorid flies could be mistaken for fruit flies, but actually, they are quite different in appearance. Phorid fly adults are tiny insects, about 1/16 to 1/8 inch long that appear to be "Humpbacked". They have yellowish-brown or black color with small head, short abdomen narrowed and dropping behind. The presence of distinctive two thickened veins near the front of the wing, terminating about halfway before the wing tip is considered a unique identifying feature of adult phorid flies. In addition, these flies have large legs with a hind femur laterally flattened (adapted for jumping). Larvae are dirty white and about 3/32 inch long. They are elongated, almost cylindrical, slightly flattened and tapered at the anterior (front) end. The puparium (a rigid outer shell formed from the larval skin that covers the pupae of most flies) is boat-shaped, about 1/8 inch long, light brown and slightly translucent. Eggs are very small (1/32 inch long) and opaque-white.
Biology
A mated female phorid fly can lay as many as 1 to 100 tiny eggs at a time, about 40 eggs in a 12-hour period or up to 750 eggs in its lifetime. The eggs are usually laid in or on suitable larval food places (decaying materials). Eggs hatch in 24 hours. Larvae go through three larval instars lasting 8 to 16 days. Pupae stage last 14 days. Newly emerged adults mate and repeat the life cycle. A study has shown that with 98% survival rate, one pair of scuttle /coffin flies in a protected place could produce 55 million flies in 60 days. Even with only 1% survival it would take only 7 months to produce 1 million flies. The life cycle from egg to adult is short and may complete in 14 days, but may take up to 37 days, depending on temperature, moisture and food availability.
Habits
Phorid flies are well known for their habits of scuttling in a fast run instead of immediately taking off when disturbed, hence their name "scuttle flies".
Although they are frequently found around flowers and moist decaying matter, they are also known to be common pests of mausoleums, mortuaries and funeral homes, where they are often referred to as "coffin flies". In these places, larvae are protected and capable of breeding inside crypts, which are inaccessible. Moreover, larvae can dig in the ground and thrive on buried human bodies. Most phorid flies are scavengers; snails, slugs, dead insects, dead animals, feces, eggs, and heavily decaying vegetation can be ideal breeding sites for these unwanted small flies. Interestingly, phorid fly larvae are also known to feed on necrotic flesh associated with wounds.
Adult flies are attracted to light. Therefore, in summer, deck and patio lights will attract them to indoor areas and once inside, they will breed where moisture and organic matter are available.
Phorid flies are also strong fliers; through the help of wind, it has been mentioned that adults are capable of traveling up to 6 miles in 24 hours and 25 miles a year.
Management
In order to manage phorid flies, you must as usual, start with the bug first; get the right identification. Wrong identification will lead to a series of unsuccessful treatment options. The best option strategy to solve the problem can be achieved by doing a thorough inspection to locate and destroy the larval breeding and feeding sources.
1. Inspection & Monitoring
Inspection
Generally, the pest management professional (PMP) is called by homeowners or building managers when they are fed up dealing with a continuance appearance of these files inside a structure. This infestation can sometimes be related to sewer pipes break and organic matter that can soak into the soil or around plumbing pipes, which provide ideal breeding sites for the developing larvae, where adults are emerging in swarms through drainpipes in affected areas. As aforementioned, these flies are attracted to light and do not live for a long time, therefore many flies can be located dead in window sells and light fixtures. Generally, in buildings, phorid flies are often found breeding in drains, trash containers, dumpsters, rotting produce, recycle bins, grease traps, garbage disposals, crawlspaces, and wherever moist organic matter can accumulate for five days or longer.
Monitoring
Because phorid fly adults are highly attracted to ultraviolet light, place insect light traps (ILTs) near places mentioned above and check periodically.Yellow sticky cards (traps) can be used for adult flies detection. Place traps just above or near where phorid flies are normally sighted or known to breed at a frequency of one per 500 to 1,000 square feet.
2. Removal of Breeding Areas
Locate and remove larval breeding sites (see above under inspection). Consider using bio-cleaning products to clean inside of the drainpipe and where organic matter may be found. A proven microbial product will eat away grease, food debris and other wastes (larvae food). Foaming bio-cleaning products are preferred forms for this work. They can reach and stick to hard-to-clean surfaces where larvae could be easily missed by using other cleaning forms. Invest enough time to bio-clean all possible larval breeding sources, including drains, under appliances, under floor mats, around plants, dumpsters, cracks and crevices, etc. Never use bleach or any types of boric acid dusts in these areas, as they will deter the bio-product being used in the cleaning. It is suggested to repeating applications at 2 to 4 week intervals depending upon the severity of infestation.
3. Pesticides
Pesticides can be used to control the adult flies, but this treatment will provide only very temporary benefit unless the source of the larval feeding and breeding is also removed. If pesticide application is needed, the PMP will use a proven aerosol or a space insecticide of pyrethrins or resmethrin to manage adult phorid flies, especially in high infestations.
The PMP also will use a proven residual insecticide and apply limited crack, crevice and spot treatments to areas where flies usually hide or rest, such as, under appliances, under floor mats, around plants, dumpsters, cracks and crevices around ceramic tile, windows, doors and grout joints, etc.
If several flies are still seen after treatment, the PMP may elect to repeat the application at 2 to 4 week intervals depending upon the severity of the infestation and the pesticide label instructions.
In some situations, it cloud be also justified to apply insect growth regulators (IGR) with volatile formulation approved and labeled for drain treatments into and around the downspout and catch basin area, as applicable.
FAQ
Q. We have a tremendous infestation of phorid flies in our apartment, which we have been battling for the last several months. To solve this problem, we hired a drain cleaning professional who cleaned all drains in the unit. This seemed to help for a while, but they returned. There is no evidence of decaying organic matter or any water leaks in the apartment. What can we do?
A. Since cleaning the drains had helped and provided a temporary relief, the phorid flies are coming for adjacent units or from any units connected to the same drainage system. Finding the source will be time consuming and expensive. Consult a professional to look at the drainage plans for the whole building. This will provide useful information about what drains are connected in the building. All units with connected drains need to be inspected for leaks and get it fixed soon.
