Answers To Fly Control Conundrums

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May 1, 1998

At the Purdue Pest Management Conference this year I presented a session called “Control of Flies in Commercial Accounts.” There were many questions, and unfortunately, I did not have time to answer all of them. I’m using this column to answer those questions and also provide a review of fly control procedures.

Q: Would fly light traps work in attics as an alternative to traditional treatment? If so, how many?

A: I assume this question concerns cluster flies. Fly light traps have been used successfully to reduce or monitor cluster fly populations in attics. As far as a replacement for traditional treatment (spraying) the critical time for exterior application is typically late summer, when the flies are beginning to enter the buildings.

Applications made after this time can be to cracks or crevices around windows and where the flies have entered. In addition, applications of encapsulated and wettable powders can reduce fly populations. Lights can work as an adjunct and are beneficial in monitoring or determining where the flies are entering. The number of traps used depends on the size of the attic and population of flies. Conceivably, you could use one trap and replace the sticky board or empty the catch tray as it fills up, eventually reducing the fly population.

Q: How many houseflies will you catch in a wall sconce trap if these flies are primarily low fliers?

A: Conceivably, these traps will catch flies if placed where the light competition is not too great and in areas where the flies are plentiful. I suspect most sconces are placed for aesthetic reasons in reception areas where the problem is small gnats or the occasional fly entering the area.

Q: How would you control flies in grocery stores with deli, seafood and salad bar departments?

A: It depends on the type of flies. Obviously, you have to seek out the source of the infestation. Both light traps and sanitation can help. Drains should be kept clean, especially the drain to the salad bar area where there is usually moisture and food debris. Even a small accumulation in a crack can become a breeding site. Pesticide application is not necessarily the answer.

Q: How do we sell UV systems if UV light will affect some surfaces?

A: This information is just emerging. UV light will affect some surfaces, including plastics. Ask your light manufacturer about this. Manufacturers are assessing the sconce’s effects on paint, tapestries, wallpaper and other materials.

Q: Methoprene has been used as an IGR against mosquitoes for years. But what about flies?

A: Good question. This control method would probably work if you can find the site at which the label allows (basically standing water). Phorid, drain and fruit flies can all breed at these sites. I can’t see using this application technique under a slab, however.

Q: Would a fly light work for phorid flies in a cemetery or mausoleum?

A: Certainly it would catch some flies.

But again, you must consider the competing UV light sources and the condition of the sanitation. I would also recommend throwing away old flowers and water that may be attracting the adult flies.

Q: What about residual application for knockdown, along with sanitation and education?

A: Products such as wettable powders and encapsulated pesticides have worked well to reduce fly populations. Read the labels carefully, spray surfaces where flies exist in high populations and use low- or no-odor materials.

Q: What is your opinion on the “drain cleaners” being promoted for fly control?

A: Actually, they are products that are promoted as drain cleaners and could affect fly populations in these drains. These products are biodegrading the organic debris the flies are breeding in but may not be a quick relief. Once drains are cleaned mechanically, they can be maintained with these products regularly. Bleach is not an acceptable drain cleaner, nor is a pesticide that affects the fly population.

Q: Can cold temperatures kill flies? How cold and in what time frame?

A: The answer depends on the stage of development and how cold it gets. The speed at which the fly is chilled can also have an impact. Fly pupae can withstand cold for extended periods of time. Also, adult flies of some species can also survive cold conditions for extended periods. While cold can cause a loss of moisture, I do not see the use of cold temperatures as a viable control mechanism.

Q: If phorid flies were breeding under a slab, would a borate solution affect them?

A: Borate affects many insects but I do not know of any application direction on borate labels for this use. Knowing the boron content of these solutions, it would probably be effective, not as a bait but as a food material containing borate.