Do Repellents Really Work?

Area repellents work by producing odors that are disagreeable or frightening to the damaging species. Some examples of area repellents are moth balls, and bars of soap hanging from trees. Predator (coyote, fox, etc.) urines have unique odors (sulfurs), detectable by other animals, and frightening to them. The main fault with area repellents is that animals lose their ability to detect an odor after repeated exposure. Contact repellents are applied directly to food items and ingested with the food. These repellents either cause illness when consumed (aversive conditioning) or give the food an objectionable odor or taste. Primary repellents are painful or irritating upon contact and causes a mammal or bird to respond reflexively. Secondary repellents are not disagreeable (aversive) immediately but produce illness or discomfort sometime after they are eaten. The effectiveness of these compounds is based on the concept of conditioning an animal to avoid the food. Contact repellents wear off or decompose fairly rapidly and applying substances to rapidly growing plants is difficult.