Bees help pollinate more than a third of the world’s crops and add an estimated value of $235 billion to $577 billion to global agriculture. They also face numerous stressors, including pathogens and parasites, loss of suitable food sources and habitat, air pollution, and climate-induced extreme weather.
A recent study revealed another important but understudied stress on bees: the “inert” ingredients in pesticides.
All pesticide products in the United States 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, dyes and the like) are considered inert.
The new study exposed honeybees to two treatments: the isolated active ingredients in the fungicide Pristine, which is used to control fungal diseases in almonds and other crops, and the entire Pristine formulation, including inert ingredients. The results were quite surprising: While the entire formulation impaired the memory of honey bees, the active ingredients alone did not have this effect.
This shows that it is actually the inert ingredients in the formula that make Pristine toxic to bees; either because inerts are toxic on their own or because combining them with active ingredients makes the active ingredients more toxic. As a social scientist focused on bee decline, I believe these findings have important implications for pesticide regulations and bee health in both cases.
What are inert ingredients?
Inert components have various functions. They can extend a pesticide’s shelf life, reduce risks for people applying pesticides, or help the pesticide work better. Some inert substances, called adjuvants, help pesticides adhere to plant surfaces, reducing pesticide drift or better penetration of active ingredients into the plant surface.
But the label “inert” is a colloquial misnomer. As the US Environmental Protection Agency states, inerts are not necessarily inactive or even non-toxic. In fact, pesticide users sometimes know little about how inerts function in a pesticide formula. This is partly because they are regulated very differently from the active ingredients.
Measuring bee impacts
Under the Federal Insecticide, Fungicide, and Rodenticide Act, or FIFRA, the EPA oversees pesticide regulation in the United States. To register a pesticide product for outdoor use, chemical companies must provide reliable risk assessment data on the toxicity of active ingredients to bees. Results of acute honeybee contact testing.
Acute contact testing monitors how honeybees respond to pesticide application over a short period of time. It also aims to determine the dose of pesticide that will kill 50% of a group of honeybees (a value known as LD50). To determine LD50, scientists apply the pesticide to the midsections of bees and then observe the bees for 48 to 96 hours for signs of poisoning.
In 2016, EPA expanded data requirements by mandating an acute honeybee oral toxicity test in which adult bees are fed a chemical, as well as a 21-day honeybee larvae test that monitors the larval reaction to an agricultural chemical from egg to emergence. as adult bees.
All of these tests, along with other data, help the agency determine what potential risk an active ingredient might pose to honeybees. Based on the information obtained from these various tests, pesticides are labeled as nontoxic, moderately toxic, or highly toxic.
A chemical black box
Despite this stringent testing, there is still much unknown about how safe pesticides are for bees. This is especially true for pesticides with lethal or chronic toxicity; that is, pesticides that do not cause immediate death or obvious symptoms of poisoning but have other significant effects.
This lack of information about sublethal and chronic effects is problematic because bees can be repeatedly exposed to pesticides on flower nectar or pollen over long periods of time, or to pesticide pollution that accumulates in beehives. They can even be exposed through miticides that beekeepers use to control Varroa mites, a destructive bee parasite.
Further complicating the issue, symptoms of non-fatal exposure are often milder or take longer to become apparent than those of acute or fatal toxicity. Symptoms may include abnormal foraging and learning ability, decreased queen egg-laying, wing deformation, stunted growth, or decreased colony survival. The EPA does not always require chemical companies to perform tests that can detect these symptoms.
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 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 is required on the label, which are often combined together and described as “other ingredients.”
Non-lethal weapons
A growing body of evidence shows that inerts are not as harmless as their name suggests. For example, exposure to two types of adjuvants (organosilicon and nonionic surfactants) can negatively impact the learning performance of honeybees. Bees rely on learning and memory functions to collect food and return to the hive; therefore, the loss of these important skills could jeopardize the survival of the colony.
Inerts can also affect bumblebees. In a 2021 study, exposure to alcohol ethoxylates, an adjuvant formula of the fungicide Amistar, killed 30% of exposed bees and caused a range 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. Studies have shown that if two or more agricultural chemicals are combined, they can become more toxic to bees than when applied alone. This is known as synergistic toxicity.
Synergy can also occur when inert substances are combined with pesticides. Another study in 2021 showed that adjuvants, which are not toxic alone, caused increased colony mortality when combined with insecticides.
A better testing strategy
Increasing evidence on the toxicity of inerts points to three key changes that could better support bee health and minimize bee exposure to potential stressors.
First, environmental risk assessments for pesticides can test the entire pesticide formulation, including inert components, to provide a more comprehensive picture of the pesticide’s toxicity to bees. This is already done in some cases but may be required for all outdoor uses where bees are at risk of exposure.
Second, inerts can be identified on product labels to enable independent research and risk assessment.
Third, more testing may be needed on long-term sublethal effects of pesticides on bees, such as learning impairment. Such research would be particularly relevant for pesticides applied to blooming plants or flowers that attract bees.
Researchers and environmental groups have been discussing similar changes since at least 2006. But because pesticide regulation is determined by federal law, changes require congressional action. This would be politically challenging as it would increase the regulatory burden on the chemical industry.
However, growing concerns about the decline of wild bees and significant annual colony losses to beekeepers make a strong case for a more cautious approach to pesticide regulation. With a growing world population and increasingly stressed food supplies, it is more important than ever to support the contribution of bees to agriculture.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and analysis to help you understand our complex world.
Written by: Jennie L. Durant, University of California, Davis.
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Jennie L. Durant worked as an Association for the Advancement of Science (AAAS) Science and Technology Policy Fellow in USDA’s Office of Pest Management Policy.