New evidence suggests that using neonicotinoids to control soybean pests may be hurting farmers.
Thiomethoxam, a neonicotinoid nerve poison, is widely applied to soybeans as a seed coating. After a bean seed is planted and it germinates and grows into a plant, every cell of the plant becomes infused with the neonicotinoid pesticide. In theory, when a pest feeds on the soybean plant, it dies from neonicotinoid pesticide exposure.
However, a 2014 study by Margaret Douglas of Pennsylvania State University and coworkers in the Journal of Applied Ecology demonstrates that slugs -- a major soybean pest -- are unaffected when they feed on neonicotinoid-treated soybean plants. However, beneficial ground beetles -- naturally abundant predators that eat slugs and normally keep them in check -- experience seizures, paralysis and death when they eat slugs from plants containing these nerve poisons.
In field trials, the researchers measured a 5 per cent yield reduction in neonicotinoid-treated soybeans compared to soybeans that did not contain the pesticide.
This is not the first study showing that using neonicotinoids on soybeans may actually reduce yields. However, it goes beyond previous studies by demonstrating in detail one mechanism by which this yield reduction occurs -- namely, killing off beneficial predatory insects.
Neonicotinoids are highly toxic to bees, earthworms, and many other organisms. Toxicity varies widely according to which group of organisms is exposed, and can also vary among species within a group. Certain pest species may be unaffected, while many non-target organisms are harmed.
Health Canada's Pest Management Regulatory Agency has approved the use of neonicotinoids for virtually every food crop grown in Canada. Pesticide and seed companies are essentially forcing farmers to use neonicotinoids in a "prophylactic" manner: applying neonicotinoids routinely and indiscriminately as seed coatings, whether or not there is evidence they are effective against the major pests of a particular crop. From the farmer's perspective of trying to grow more food at a lower cost, it is increasingly evident that neonicotinoids are being used in unacceptable ways. From an environmental perspective, the evidence of harm is overwhelming.
This new study by the Pennsylvania State University researchers is important for another reason -- it demonstrates how neonicotinoids are affecting organisms at higher levels in the food chain.
When Dutch researchers published a study last year showing that bird populations are declining fastest in areas with the highest levels of neonicotinoid water pollution, they were not sure how birds are being harmed. Direct consumption of neonicotinoid-coated seeds can be fatal to seed-eating birds. But what about insect-eating birds? One possibility is that neonicotinoids are eliminating their food resources: swallows, swifts, flycatchers, etc. are finding fewer insects to feed on. Another possibility is that these species are poisoned by neonicotinoids in the insects they are eating. In fact, both scenarios could be operating at the same time -- birds are finding fewer insects, and their nervous systems are damaged by neonicotinoids in the insects they are able to find -- a sort of "double whammy."
Populations of birds, bats, bees, aquatic insects and frogs are all in decline. Human activities affect the environment in so many ways that none of these declines can with certainty be attributed to a single cause. Chemical companies exploit this uncertainty. For example, they suggest that mite infestations are a larger contributor to honey bee colony collapse than neonicotinoid pesticides. But when there is such overwhelming evidence that neonicotinoid pesticides are poisoning the environment, and also reducing farmers' profits in some circumstances, it is time to act.
Ole Hendrickson is a forest ecologist and current president of the Ottawa River Institute, a non-profit charitable organization based in the Ottawa Valley.
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