Posted by Jennifer Hojnacki, Mon, Aug 27, 2012
According to the calendar, summer is winding down, but at least here in the Midwest the flies don’t seem to have gotten the message. Just sitting on the porch can be a workout as you swat at them, never mind heading into the barn or pasture or onto the trails, where flies have lots of moist environments in which to breed and congregate. So, while you may have hoped to have purchased your last fly control product in July, late August and September may find you once again in the fly spray aisle trying to figure out which product works best.
One of the things horse owners find most confusing about fly sprays is the ingredients themselves. The two primary ingredients used in commercial fly sprays (pyrethrin and permethrin) even sound similar, so no wonder we’re all confused! Here’s a short primer on the differences between the two.
Pyrethrin
Pyrethrin is derived from the parent chemical pyrethrum, to which you’ll sometimes hear people refer when they’re talking about pyrethrin. It is produced by a certain species of the chrysanthemum plant. Pyrethrins are contact poisons that work by quickly penetrating the shell or skin of the insect, paralyzing its nervous system. It’s important to understand that while pyrethrins are powerful “knockdown” agents, they aren’t actually killing the insect; a fly’s enzymatic system degrades or detoxifies the pyrethrin, allowing some of them to recover. For this reason, many fly spray manufacturers add synergists (more on that in a minute) to their formulas to help delay the insect’s enzyme action, assuring a lethal dose.
Permethrin
Permethrin is a synthetically produced insecticide that, like pyrethrin, works as a neurotoxin, overstimulating the nervous system on contact. Similarly, permethrin’s knockdown capabilities are often combined with synergists in order to actually kill the insects. Permethrin is more stable than pyrethrin, so formulas containing permethrin typically can provide longer protection.
A note about repellents and synergists: Repellants, unlike the compounds listed above, discourage flies and help to keep them away from your horse, but don’t actually knock them down or kill them. The most common repellent found in fly sprays is butoxypolypropylene glycol. As mentioned above, synergists are used in fly sprays to increase the potency of the pyrethrin and/or permethrin in the formula by inhibiting the enzymatic activity within the insect that breaks down the insecticide and allows the fly to get back up again. The synergists you’ll see most often in fly sprays for horses are piperonyl butoxide and bicycloheptene dicarboxamide.
So, are these chemicals safe? Pyrethrin and permethrin are both classified as “Restricted Use Pesticides” by the EPA, which means that their use in products is restricted to certified manufacturers. That said, they are considered relatively nontoxic to mammals (including humans). Because pyrethrin is derived from a natural source (the chrysanthemum flower), it is readily biodegradable when exposed to oxygen, moisture, and sunlight and so is not considered particularly dangerous to the environment. Permethrin also breaks down fairly easily and is not associated with any significant environmental issues. It should be noted, however, that pyrethrin is highly toxic to fish and moderately toxic to birds and bees, and permethrin is fatal to cats and fish and highly toxic to bees and other beneficial insects, so take care when using fly sprays containing these compounds if you have any of these other species on your property.
The active ingredient in Pro-Force® is permethrin. Proven to repel and kill more than 70 species of pest, this spray is highly versatile and can even be used on dogs.
