[Tech Talk] Beneath Our Feet — Solving Phorid Fly Issues Below the Slab

Last month’s Tech Talk column focused on eliminating all other possibilities to ensure that a phorid fly issue is indeed coming from below the slab and determining the right location to begin your corrective work. This month, we focus on how to implement corrective action.

Invariably, the solution to sub-slab phorid flies means digging up the floor. Because the price tag is usually quite high, few companies are willing to take an active role in the process. This is unfortunate as it takes a pest management professional to help confidently guide a facility through rocky waters of sub-slab remediation. And, less aggressive methods may not solve the real problem.

If you can convince your client to take the steps required to permanently solve this issue and you have confidently identified the starting point of the problem, begin where the activity is the greatest. It is vital that you know from observation or direct evidence that the flies will be there when concrete comes up.
 

The Nitty-Gritty.

Before anyone puts carbide to concrete, the details of moving appliances and furnishings should be settled. The location of power lines and other utilities that may lie in or beneath the slab should be established as accurately as possible. It is not unusual for the actual positions of pipes and wires to be alarmingly different than the drawings. The actual deconstruction of the floor and subsequent removal of the fill should be performed by the facility’s engineering department or a competent mechanical contractor. It is extremely common for surprises and complications to require the sort of on-site adjustment that is best done by an experienced contractor. A talented mechanical contractor is as vital to the process as the PMP.

There will be concrete, rebar and contaminated fill that will require disposal. The best method I have seen is the use of concrete saws to remove concrete and vacuum trucks to remove contaminated fill. Disposal of the fill should be arranged ahead of time and state or local regulations may apply. You should be present for the opening and remain on site as work progresses. Some important clues and details may only be visible for a short time. Periodically examine the area for larvae and pupae. This may be difficult, but a sharp eye can recognize the sometimes subtle clues that indicate “pay dirt.” The larvae are most often found under the pipe and can be hard to see when embedded in the dark, soupy matrix of decay. You may need to use the low angle technique with a quality flashlight and wait for the maggots to move.

Wear sturdy work boots, coveralls and gloves. Thick, dependable, re-useable gloves that can be washed and sanitized are best, but some prefer disposable nitrile gloves. If you choose disposable gloves, ensure that they are at least 5 mils thick and be prepared to change them often as sharp objects may cause them to tear. If the problem involves sewage, there may be dangerous pathogens associated with the environment.

It is important to find and repair all the faulty plumbing, but it is equally important to remove all of the contamination. It has happened that contractors working without a pest professional in attendance have quickly found and repaired the plumbing fault and re-poured the slab only to tear it all back up later because they failed to remove the actual source. The flies will continue until the larvae, pupae and contaminated fill are removed. The operation should continue in all directions until the fill is clean and no more larvae or pupae can be found.

There could be a point where emotions rise beyond the levels of common sense and heated exchanges may occur. It will serve you well to remain calm and take responsibility only for your area of expertise. It is often helpful to remind those ultimately in charge that the only thing worse than digging up the floor is digging up the floor twice. This author has had the memorable experience of pointing out that the only thing worse than digging it up it twice is digging it up three times!
 

Details, details.

Be sure to keep detailed notes and pictures for future reference. Some facilities have strict rules against taking pictures, but there are almost always provisions for exceptions. The value of well-taken pictures cannot be over-stated. Use a quality camera and a competent photographer if you are not one. Should there be trouble, images can be invaluable in answering questions and determining the next steps. Be sure to get images that document the opening of the slab, the state of the fill beneath, flies in the environment (including both larvae and pupae) and anything else that may be important.

Once the process is complete and the floor replaced, change the glue-boards in all the ILTS and resume monitoring. Within 24 hours of completing the job, trap catch should drop to zero. A fly or two is no cause for panic. One week of zero flies caught is usually sufficient to indicate success. Because the pupal period of the two most common species is about two weeks, you may want to delay the celebration until the second week is complete, but for most cases, success is quickly evident.

Generate a final report using pictures and notes that document the entire process and be sure to make notes to yourself on how you would improve the process for future adventures.

Rose Pest Solutions’ Mark Sheperdigian is a 1982 graduate of Michigan State University with a bachelor’s degree in entomology. He has held a variety of positions in service, sales, management and technical support. He is vice president of technical services for Rose Pest Solutions in Troy, Mich.

Copesan is an alliance of pest management companies with locations throughout North America. To learn more, visit www.copesan.com.