Bees help pollinate more than a third of the world’s crops, and contribute an estimated $235 to $577 billion in value to global agriculture. They also face a host of stressors, including pathogens and parasites, loss of suitable food sources and habitats, air pollution and climate-related weather extremes.
A recent study has identified another important but under-researched pressure on bees: ‘inert’ ingredients in pesticides.
All pesticide products in the US contain active and inert ingredients. Active ingredients are designed to kill or control a specific insect, weed or fungus and are listed on product labels. All other ingredients – emulsifiers, solvents, carriers, aerosol propellants, fragrances, colorants and the like – are considered inert.
In the new study, honey bees were exposed to two treatments: the isolated active ingredients in the fungicide Pristine, which is used to combat fungal diseases in almonds and other crops, and the entire Pristine formulation, including inert ingredients. The results were quite surprising: the entire formulation affected the honey bees’ memory, while the active ingredients alone did not.
This suggests that the inert ingredients in the formula actually made Pristine toxic to bees – either because the inerts were toxic on their own, or because their combination with the active ingredients made the active ingredients more toxic. As a social scientist focused on bee decline, I believe these findings have important implications for pesticide regulation and bee health.
What are inert ingredients?
Inert ingredients have different functions. They can extend the shelf life of a pesticide, reduce risks for people who apply the pesticides, or make a pesticide work better. Some inert substances, called adjuvants, help pesticides adhere to the plant surface, reduce pesticide drift, or allow active ingredients to better penetrate the surface of a plant.
However, the “inert” label is an informal misnomer. As the U.S. Environmental Protection Agency notes, inert substances are not necessarily inactive or even nontoxic. In fact, pesticide users sometimes know very little about the action of inert substances in a pesticide formulation. That’s partly because they are regulated very differently than active ingredients.
Measuring bee effects
Under the Federal Insecticide, Fungicide, and Rodenticide Act, or FIFRA, the EPA oversees pesticide regulation in the US. To register a pesticide product for outdoor use, chemical companies must provide reliable risk assessment data on the toxicity of the active ingredients to bees, including the results of an acute honey bee contact test.
The acute contact test quickly monitors how honey bees respond to a pesticide application. It is also intended to determine the dose of a pesticide that will kill 50% of a group of honey bees, a value known as the LD50. To determine the LD50, scientists apply the pesticide to the bees’ bellies and then observe the bees for 48 to 96 hours for signs of poisoning.
In 2016, the EPA expanded its data requirements by requiring a test for acute oral toxicity in honeybees, in which adult bees are administered a chemical, as well as a 21-day test on honeybee larvae that monitors the larvae’s response to an agrochemical, starting the egg until their emergence. as adult bees.
These tests all help the agency determine what potential risk an active ingredient may pose to honeybees, along with other data. Based on the information from these various tests, pesticides are labeled as non-toxic, moderately toxic or highly toxic.
A chemical black box
Despite these rigorous tests, much remains unknown about how safe pesticides are for bees. This is especially true for pesticides with sublethal or chronic toxicity – in other words, pesticides that do not cause immediate death or obvious signs of poisoning, but have other significant effects.
This lack of knowledge about sublethal and chronic effects is problematic because bees may be exposed repeatedly for extended periods of time to pesticides on flower nectar or pollen, or to pesticide contamination that accumulates in beehives. They can even be revealed through miticides that beekeepers use to control Varroa mites, a devastating bee parasite.
Complicating the problem further is that the symptoms of sublethal exposure are often more subtle or take longer to become apparent than acute or fatal toxicity. Symptoms may include abnormal foraging and learning abilities, reduced egg-laying by the queen, wing deformation, growth retardation or reduced colony survival. The EPA does not always require chemical companies to perform the tests that can detect these symptoms.
Inert ingredients add another level of mystery. Although the EPA reviews and must approve all inert ingredients, the same toxicity testing is not required as for active ingredients.
This is because under FIFRA, inert ingredients are protected as trade secrets or confidential business information. The label only requires the total percentage of inert ingredients, often lumped together and described as “other ingredients.”
Sublethal weapons
A growing body of evidence suggests that inert substances are not as harmless as the name suggests. For example, exposure to two types of additives – organosilicones and nonionic surfactants – can hinder honeybees’ learning performance. Bees rely on learning and memory functions to gather food and return to the hive, so losing these crucial skills can jeopardize the survival of a colony.
Inert substances can also affect bumblebees. In a 2021 study, exposure to alcohol ethoxylates, a coformulant in the fungicide Amistar, killed 30% of bees exposed and caused a number of sublethal effects.
Although some inert substances are not toxic on their own, it is difficult to predict what will happen when they are combined with active ingredients. Research has shown that when two or more agricultural chemicals are combined, they can become more toxic to bees than when applied separately. This is known as synergistic toxicity.
Synergism can also occur when inert substances are combined with pesticides. Another 2021 study showed that adjuvants that were not toxic on their own caused increased colony mortality when combined with insecticides.
A better testing strategy
Growing evidence on the toxicity of inert substances points to three key changes that could better support bee health and minimize bee exposure to potential stressors.
First, environmental risk assessments for pesticides could test the entire pesticide formulation, including the inert ingredients, to provide a more complete picture of a pesticide’s toxicity to bees. In some cases this is already done, but it may be necessary for all outdoor uses where bees are at risk of exposure.
Secondly, inert substances could be identified on product labels to enable independent research and risk assessment.
Third, more tests may be needed to investigate the long-term sublethal effects of pesticides on bees, such as learning disabilities. Such research would be especially relevant for pesticides applied to flowering crops or flowers that attract bees.
Researchers and environmental groups have been calling for these kinds of changes since 2006. However, because pesticide regulation is dictated by federal law, changes require action from Congress. This would pose a political challenge as it would increase the regulatory burden on the chemical industry.
Nevertheless, growing concerns about bumblebee declines and beekeepers’ significant annual colony losses make a strong case for a more precautionary approach to pesticide regulation. As the world population grows and food supplies come under increasing pressure, supporting the contribution of bees to agriculture is more important than ever.
This article is republished from The Conversation, an independent nonprofit organization providing facts and analysis to help you understand our complex world.
It was written by: Jennie L. Durant, University of California, Davis.
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Jennie L. Durant has served as a Science and Technology Policy Fellow at the Association for the Advancement of Science (AAAS) in the USDA’s Office of Pest Management Policy.