U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

January 2001


A pesticide is a substance intended for destroying, repelling or mitigating any animal, microorganism or plant pest. While pesticides are commonly chemical agents, biological or physical agents can also be pesticides. Many people equate the term pesticide with insecticide. However, there are a plethora of pesticides for which insects are not the target pest. Examples include herbicides, fungicides, rodenticides, acaricides, larvacides, etc. Additionally, pesticides are not limited to toxicants, but also include repellents, attractants and growth regulators (1 ) .

Pesticides are nearly ubiquitous in today's world. In agriculture, insecticides, nematicides and herbicides are applied to plants and soil to improve the yield andor the appearance of the harvested commodities (2). Such uses are common knowledge among the populace. A variety of other uses of pesticides are less obvious to the average citizen, but are widespread nonetheless. For example, insecticides and rodenticides are released into the environment in an effort to decrease populations of pathogen carrying animals such as insects and rodents. Pesticides such as mildicides and insecticides are routinely incorporated into building materials andor applied to structures to prevent pest infestation. Pesticides are routinely applied to boat bottoms to prevent the attachment and growth of a mollusks. The list goes on and on.

The ubiquitous nature of pesticides suggests that exposure to wildlife is inevitable. Primary exposure results from wildlife directly consuming the pesticide formulation. Primary exposure scenarios include birds feeding on granular insecticide formulations, squirrels consuming rodenticide baits intended for rats, or wildlife being exposed to pesticide drift resulting from the spray application of an insecticide in an agricultural situation. Secondary exposure results from the consumption of animals containing pesticide residues. Secondary exposure scenarios include scavenging mammals such as ferrets, feeding on rodent carcasses containing rodenticide residues. Tertiary exposure results from another animal such as a raptor feeding on the secondarily exposed ferret in the previous example. Unfortunately, the possible routes of non-target exposure of wildlife to pesticides are varied and many.

Pesticides are bioactive compounds. As such, pesticides exert biological effects on living organisms (3). Fortunately, most pesticides are somewhat selective. The intended effect of the pesticide is usually more pronounced towards the target species than non-targets. Selectivity can also be enhanced by adopting application practices to minimize non-target exposure. However, even in the best of situations, selectivity is less than absolute. Thus, when non-target wildlife are exposed to pesticides, unintended biological effects often follow.