COMMON INGREDIENTS
IN FLY- CONTROL PRODUCTS FOR HORSES
Before discussing the particulars of formulas, it’s important to understand the distinction between insecticides and repellents. Insecticidal products deter flies from landing on a horse and, through a variety of biological mechanisms, kill those that do. Repellents do not kill insects but discourage them from landing by masking the horse’s scent or by interfering with the insect’s prey-detection capacity. Some products are marketed only as insecticides or repellents, others as both. But when reading the label of any fly-control product you are likely to see one or more of these active ingredients:
Pyrethrin, a natural compound derived from a type of chrysanthemum, kills insects quickly through neurologic hyperexcitation, loss of motor coordination and paralysis. Pyrethrins can be broken down by sunlight, so special synergists are often added to extend the effectiveness of pyrethrin formulas (read more about one of the most common synergists later).
Pyrethroids are synthetic forms of pyrethrin, and kill insects with the same action. Some of the most common ones found in fly sprays are permethrin, cypermethrin, tetramethrin and resmethrin. Pyrethroids are not as easily broken down by sunlight, so their effectiveness can last for several days.
Piperonyl butoxide is a common synergist—it doesn’t kill insects by itself, but inhibits enzymes within the insect’s bodies, giving pyrethrins more time to work. Insects are less likely to recover from an insecticide that contains piperonyl butoxide.
Picaridin is a synthetic insect repellent that mimics a natural chemical called piperidine, found in the species of plants that includes common black pepper. Picaridin is thought to work by blocking an insect’s ability to sense its prey. Picaridin is used in a combination spray product intended to be used on horses and humans.
Oils, such as citronella, cedar or tea tree, are typically used in repellents as they have strong scents that insects generally avoid, but can also be added to insecticides.