by Bees help pollinate more than a third of the world’s crops, contributing an estimated value of between $235 billion and $577 billion to global agriculture. They also face myriad stresses, including pathogens and parasites, loss of suitable food sources and habitat, air pollution, and climate-driven extreme weather events.
A recent study has identified another important but understudied pressure on bees: the “inert” ingredients of pesticides.
All pesticide products in the US contain active and inert ingredients. The 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 so on) are considered inert.
The new study exposed bees to two treatments: the isolated active ingredients of the Pristine fungicide, which is used to control fungal diseases in almonds and other crops, and the entire Pristine formulation, including the inert ingredients. The results were quite surprising: the entire formulation impaired the bees’ memory, while the active ingredients alone did not.
This suggests that the inert ingredients in the formula were actually what made Pristine toxic to bees, either because the inerts were toxic on their own or because combining them with the active ingredients made the active ingredients more toxic. As a social scientist who focuses on bee declines, I think either way these findings have important implications for pesticide regulation and bee health.
What are inert ingredients?
Inert ingredients have a variety of functions. They can extend the shelf life of a pesticide, reduce risks to people who apply it, or help a pesticide work better. Some inerts, called adjuvants, help pesticides stick to plant surfaces, reduce pesticide drift, or help active ingredients penetrate better into plant surfaces.
However, the label “inert” is a colloquial misnomer. As the U.S. Environmental Protection Agency points out, inerts are not necessarily inactive or even non-toxic. In fact, pesticide users sometimes know very little about how inerts work in a pesticide formulation. This is partly because they are regulated very differently than active ingredients.
Measuring the effects of bees
Under the Federal Insecticide, Fungicide, and Rodenticide Act, or FIFRA, the EPA oversees pesticide regulation in the U.S. To register a pesticide product for outdoor use, chemical companies must provide reliable risk assessment data on the toxicity of active ingredients to bees, including results of an acute contact test with bees.
The acute contact test tracks how bees react to the application of a pesticide over a short period of time. It is also intended to establish the dose of a pesticide that will kill 50% of a group of bees, a value known as LD50. To determine the LD50, scientists apply the pesticide to the abdomen of bees and then observe them for 48 to 96 hours for signs of poisoning.
In 2016, the EPA expanded its data requirements by requiring an acute bee oral toxicity test, in which adult bees are given a chemical, as well as a 21-day bee larval test that tracks the reaction of bees. larvae to an agrochemical from the egg to their appearance. like adult bees.
All of this testing helps the agency determine what potential risk an active ingredient may pose to bees, 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 this rigorous testing, much is still unknown about how safe pesticides are for bees. This is particularly true for pesticides that have sublethal or chronic toxicities; 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 over long periods of time to pesticides in nectar or floral pollen, or to pesticide contamination that accumulates in hives. They may even be exposed through acaricides that beekeepers use to control Varroa mites, a devastating bee parasite.
Complicating the problem, symptoms of sublethal exposure are often more subtle or take longer to become apparent than acute or lethal toxicity. Symptoms may include abnormal foraging and learning ability, decreased egg laying by the queen, wing deformation, delayed growth, or decreased colony survival. The EPA does not always require chemical companies to perform tests that can detect these symptoms.
The inert ingredients add another level of mystery. While the EPA reviews and must approve all inert ingredients, it does not require the same toxicity testing as for active ingredients.
This is because under FIFRA, inert ingredients are protected as trade secrets or confidential business information. Only the total percentage of inert ingredients, often grouped together and described as “other ingredients,” are required on the label.
Sub-lethal weapons
A growing body of evidence suggests that inerts are not as harmless as the name suggests. For example, exposure to two types of adjuvants (organosilicon and nonionic surfactants) can affect the learning performance of bees. 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.
Inerts can also affect bumblebees. In a 2021 study, exposure to alcohol ethoxylates, a coformulant of the fungicide Amistar, killed 30% of exposed bees and caused a number of sublethal effects.
While some inerts may not be toxic on their own, it is difficult to predict what will happen when combined with active ingredients. Research has shown that when two or more agrochemicals are combined, they can become more toxic to bees than when applied alone. This is known as synergistic toxicity.
Synergism can also occur when inerts are combined with pesticides. Another 2021 study showed that adjuvants that were not toxic alone caused increased colony mortality when combined with insecticides.
A better testing strategy
Growing evidence on the toxicity of inerts points to three key changes that could better support bee health and minimize their exposure to potential stressors.
First, environmental risk assessments of pesticides could test the entire pesticide formulation, including inert ingredients, to provide a more complete picture of a pesticide’s toxicity to bees. This is already done in some cases, but may be necessary for all outdoor uses where bees are at risk of exposure.
Second, inerts could be identified on product labels to allow for independent investigation and risk assessment.
Third, more evidence may be needed on the long-term sublethal effects of pesticides on bees, such as impaired learning. This research would be especially relevant to pesticides applied to flowering crops or flowers that attract bees.
Researchers and environmental groups have been advocating for changes like these since at least 2006. However, because pesticide regulation is dictated by federal law, changes require congressional action. This would be a political challenge as it would increase the regulatory burden on the chemical industry.
However, growing concerns about bumblebee declines and significant annual colony losses by beekeepers make a strong argument for a more precautionary approach to pesticide regulation. With a growing global population and food supplies under increasing pressure, supporting bees’ contribution to agriculture is more important than ever.
This article is republished from The Conversation, an independent, nonprofit news organization bringing you data 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 worked as a science and technology policy fellow at the Association for the Advancement of Science (AAAS) in the USDA Office of Pest Management Policy.
