Pest management is a problem-solving profession. A customer has a problem with an infestation of some pest, and it is the pest professional’s job to solve it. Each situation is different, with many factors influencing an infestation — the type of pest involved, number of pests present, construction and maintenance of the building, contributing conditions, and sanitation practices.

Experience is the best teacher in the pest management profession. One can learn all about a pest’s biology and habits, but until he or she deals with that pest in actual situations, the professional will not appreciate just how different pests act and live in the field. A skilled professional learns from his mistakes — and his successes. As he progresses in his career in pest management, his ability to solve pest infestations will increase with each experience.

Review of “case studies” is a good way to pass knowledge learned to other pest professionals. The following cases describe situations involving fly infestations in structures. Here are four case studies — two about small flies and two about filth flies — that might be similar to a current situation you’re facing.

Small Flies Case #1 — Fruit Flies & Fungus Gnats

A 40-story office building reported flies in the offices on the first six floors. No live flies could be found during an inspection of the offices on these floors. The customer also had failed to collect any specimens as they had been asked to do on the day prior to the inspection. By inspecting window sills, dead fruit flies were found in some offices on floors 2 through 5 but not on the sixth floor. Fungus gnats, however, were found on the sixth floor.

Further investigation showed that the fungus gnats were living in the soil of potted plants on employees’ desks. These plants were being overwatered, which promoted the growth of fungi in the soil. The employees were educated on proper watering procedures and were asked to allow the soil to thoroughly dry to kill the fungus gnat larvae.

Fruit fly, Drosophila melanogaster
© Stoy Hedges

The fruit flies proved more challenging. Inspections of drains, coffee stations, trash containers and restrooms revealed no fruit flies or breeding sites. The lowest floor of this building was a garage and loading dock, and an elevator that ran up to all floors was located in the loading dock area. A trash dumpster was found in the loading dock area approximately 75 feet from the elevator. An inspection of the dumpster revealed that garbage and wet, decaying organic debris had been allowed to accumulate under the dumpster. It appeared that the underneath of the dumpster had not been cleaned in some time. Fruit fly larvae, as well as blow fly larvae, were found living in the organic debris under the dumpster. Hundreds of fruit fly adults were seen flying about the loading dock area.

Fungus gnat

The fruit flies were attracted to the lights in front of the elevator and entered the elevator when the doors opened. The flies then would fly out onto the various floors when the elevator opened and proceeded to fly about the different offices. The office building’s management was shown the dumpster area and was provided a list of written recommendations. The primary recommendation was to establish a regular cleaning schedule of the dumpster to prevent problems of this type from occurring in the future. No insecticide treatments were needed to solve this problem.

Lessons Learned: The breeding source is not always near the area where flies are seen. Sometimes, it can be a good distance from that area.

Small Flies Case #2 — Fruit Flies

A homeowner was experiencing a problem with fruit flies. Inspections of trash containers and the pantry did not reveal any flies or fly larvae. The flies were found breeding in the garbage disposal in the kitchen. Cleaning the disposal subsequently solved the problem.

Lessons Learned: Even garbage disposals need regular cleaning to prevent them from becoming breeding sources for flies.

Filth Flies Case #1 — House Flies

House fly, Musca domestica

While performing a routine quality control check in a hotel kitchen, an entomologist noticed that a large number of house flies were present in the kitchen. During the inspection, a number of brown fly pupae were found on the floor beside a stove. Closer inspection of this area revealed numerous fly pupae on a shelf under a table next to the stove. Two boxes of potatoes were stored on this shelf. The top box contained clean, fresh potatoes. The bottom box, however, contained rotting potatoes in which large numbers of house fly larvae and pupae could be found. Evidently, an employee placed a new box of potatoes on top of a box in which all of the potatoes had not been used. The second box was overlooked and potatoes began to rot, creating a breeding source for the house flies. Removing the infested box of potatoes and cleaning the area thoroughly solved the infestation. A space treatment was applied to kill the remaining adult flies.

Lessons Learned: Although house flies do not generally breed indoors, it does occasionally happen. Usually a situation as described here is involved or a trash receptacle has not been cleaned properly. Always be on the look out for fly pupae when inspecting.

Filth Flies Case #2 — House Flies & Blow Flies

A hotel was experiencing a problem with flies in its restaurant kitchen. The kitchen had a short hallway that led to a back door located by the dumpster area. The dumpster area was cleaned regularly and no fly breeding sources could be found. The dumpster also was surrounded by a concrete block wall and was located only 12 feet from the hotel’s back door. Unfortunately, even clean dumpsters attract flies. The dumpster’s close proximity to the door attracted flies to the area of the door where they entered as the door was opened and closed.

Whoever designed the hotel provided a feature that ultimately helped control flies inside the building. The back door opened into a small entry vestibule which had an additional doorway into the kitchen. A corner-mounted ILT was mounted in the corner of the entryway to the right of the door and facing away from the door (see figure at right). Most of the flies and other flying insects entering the door from outside were eventually attracted to and captured by the ILT before they could enter the kitchen. Subsequent checks of the trap’s catch pan showed that flies, beetles, yellowjackets and moths were captured by the trap.

In addition to the installation of the light trap, a schedule of monthly insecticide applications to the walls around the dumpster where flies often rested was instituted. These treatments of fly-resting areas further reduced the number of flies in the area of the back door.

Lessons Learned: One properly placed insect light trap can be invaluable in solving a fly infestation.

The dumpster was located too close to the back door of a hotel. Installation of two ILTs in the darkened, covered entryway captured flies and flying insects before they could enter.