The Curious Beekeeper
The Perils of Pyrethroids for Pollinator
Just after 9 p.m., the faint rumble of a mosquito truck tumbles through the open windows of my South Dakota home. As the sound gets louder, I drop my book and scramble to close everything, slamming windows and doors to keep the fog outside. Sometimes I watch as the truck thunders by, spewing poisonous white clouds into the evening sky.
Normal people think I’m crazy, and that’s likely true. My loathing for pesticides is especially odd considering I’m trained to recommend which one to use on your crop, when, and at what concentration. But my formal education made me more wary of pesticides, not less. With only occasional exceptions, I’ve steered clear of them most of my life.
The dose makes the poison
I once took a graduate course in herbicide science — the organic chemistry of killing plants. What impressed me most was the chemical similarity between plants and animals. Basically, all living things on Earth comprise the same stuff: the same molecules, amino acids, and trace minerals.
When you think about it, the similarity between plants and animals makes sense because all animal life depends on plants. While some animals eat plants, others eat animals that eat plants. The nutrients stored within a plant become the building materials for everyone in the food chain.
Because life-forms have similar physiology, any chemical that harms a plant may harm an animal. Although some chemicals are selective, meaning they harm some organisms but not others, others are toxic for many.
When using pesticides, we can often lessen collateral damage by controlling dosages, to wit: “The dose makes the poison.” Since the amount of poison compared to an animal’s size is important, dosage is paramount in avoiding harm. Avoiding harm to animals was a major focus of my course in herbicides, which tells you something.
Now think about this: If a poison designed to kill plants can be dangerous to animals, imagine how dangerous a poison intended to kill one type of animal can be to another. If someone is sloppy about using the recommended dosages, we can get multiple unintended consequences.
A common myth about pyrethroids
Unfortunately, misconceptions about the toxicity of certain insecticides, especially pyrethroids, are rampant. People often use them to spray their lawns and gardens, believing they are safe for bees. Some folks even treat their flower gardens with pyrethroids, hoping to spare them from aphids.
We cling to the myth that modern pyrethroids are simply squeezed from chrysanthemums, an idea that provides comfort. After all, if insecticides come from chrysanthemums, they’re safe, right?
The truth is more complex. Originally, pyrethrins came from the dried flower heads of Chrysanthemum cinerariifolium, a daisy-like species native to the Balkans, also called the dalmatian chrysanthemum. Later, Chrysanthemum coccineum, or painted daisy, was also a source of these natural pesticides.1
The word “pyrethrum” refers to the suite of insecticidal chemicals extracted from a specific species, while “pyrethrin” describes an individual chemical found within the pyrethrum. The number of pyrethrins found in chrysanthemums varies with the species and ranges from none to six …
