Are pesticides really drugs?
By Chris Williams on March 11, 2013.
Way back in the late seventies when I was an undergraduate entomology student (geez I’m getting old!) I took a class in ‘economic entomology’. It gave a basic overview of the economic impact of insects to human beings in terms of crop losses, property damage, and human health. It was the first (and last) time I’d ever heard of pesticides being referred to as ‘economic poisons’ too. Just for ‘fun’ I looked up the term and according to Merriam-Webster, it means: a substance or mixture of substances (as an insecticide, fungicide, rodenticide, or herbicide) for control of plants or animals that have economic significance as pests (as in agriculture, industry, or households). The reality is, that these substances are DRUGS.
If there were another version of me in some parallel universe I’d probably be a pharmacist. Why? Some of my favorite college courses were in biochemistry and toxicology. Just knowing that an insecticide works is good enough for most people and most of my colleagues, but not me. I’m fascinated by what these drugs (oops, sorry pesticides) do. Still not convinced these compounds are drugs? One class of insecticide my industry used to use a lot belonged to the group known as carbamates. While there aren’t many of them left in the marketplace, a common one for backyard growers called carbaryl (Sevin) still is. Carbamates affect acetylcholine receptors in nerve cells and are sometimes used in anesthesia. Another drug discovery that has made its way into the insecticide market are the avermectins. These natural compounds produced by a bacterium (Streptomyces avermitilis) were first discovered in 1976 by researchers at Merck looking for new ways to treat intestinal parasites, (roundworms, tapeworms etc) in animals and humans. As it turns out, these moderately toxic compounds have insecticidal activity too, and have made their way into bait formulations for ant and cockroach control.
The insect central nervous system has many similarities to the human CNS and provides a wide variety of target sites for these various insecticides (or drugs if you prefer) to operate. The common classes (pyrethroids, carbamates, neonicotinoids etc) all work as disruptors of various biochemical processes occurring within the neuron. Other compounds like hydramethylnon (the active ingredient in the original cockroach bait Combat) have a completely different mode of action. If you ever used the product, you may have noticed that insects exposed to hydramethylnon die face down. Why? Because it works to shut down energy production within the insect’s cells eventually stopping them dead in their tracks. Still other materials disrupt the insect’s muscle control or block the formation of the insect’s exoskeleton. So are these compounds drugs? I think so. You may disagree if you like!
For the other true geeks out there like me, the following link will give you all the information you’d ever want to know about insecticides and their modes of action.