Catnip Oil Tested as Stable Fly Repellent

Anyone who's ever set foot on a farm has most likely encountered the plaguelike presence of Stomoxys calcitrans--otherwise known as stable flies. These pests are both an annoyance and a health risk for horses, but the results of a recent study indicate that a common treat for cats might be the answer barn managers are looking for.

"Horses are very, very sensitive to stable flies," said David Taylor, PhD, a research entomologist with the USDA. "Cattle will acclimate (to the flies) but one or two flies on a horse and that horse is much more difficult to handle." Additionally, stable flies are known to transmit diseases such as equine infectious anemia.

Junwei J. Zhu, PhD, a research entomologist with the USDA-Agricultural Research Service (ARS), and Christopher Dunlap, PhD, a research chemist with the USDA-ARS, recently conducted a study to see if catnip oil might help repel stable flies from barns. According to Zhu, catnip has been shown to repel more than 13 families of insects, including mosquitoes, since scientists began investigating the material in the 1970s.

In order to test the efficacy of catnip as a fly repellent, Zhu and his team (in collaboration with specialists from the University of Nebraska's Entomology Department) crafted both oil- and water-based repellents from the plant's active ingredient compounds (nepetalactones) and spread the repellents in areas frequented by cattle to assess the reactions of the stable flies.

"When they smell (the catnip), they will fly away abruptly and not return until the smell is completely gone," Zhu said.

Currently the only methods for controlling stable fly populations include the removal of waste (the flies' reproduction site) and rigorous insecticide applications. Zhu added that an effectual insecticide targeting this particular species is not available on the market.

Zhu's recent study indicates that catnip oil offers livestock handlers a safe, direct way to combat these pests. Not only does the oil repel stable flies, it also poses no risk to horses or other livestock and has the additional benefit of being a "green technology." Since the repellent would be derived from the catnip plant, it could be used by organic farmers who don't want to contaminate their products with unnatural chemicals. In addition, the oil has been shown to destroy stable fly larvae, effectively addressing this problem at its source.

One downside, according to Dunlap, is that catnip oil is highly volatile, meaning it disperses quickly, losing its efficacy within six hours. In order to produce a viable repellent, a controlled-release formulation must be developed, he added.

Along with repellents, Zhu's team is also investigating attractants, employing a "push and pull" strategy to push the flies out of livestock quarters and into traps where they can be eliminated.

The study, "Repellency of a wax-based catnip oil formulation against stable flies," was published in the Journal of Agriculture Food and Chemistry in late 2010. The abstract is available online.

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