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Daily News Blog

29
Aug

Pollinator Health: Common Fungicide Linked to Changes in Honey Bees’ Brain through Oxidative Stress

Honeybees, a pollinator species, surrounding their hive

(Beyond Pesticides, August 29, 2023) A study published in Insect Biochemistry and Molecular Biology finds the widely used azole fungicide, tebuconazole, has damaging impacts on the redox homeostasis (the process of maintaining balance between oxidizing and reducing reactions) and fatty acid composition in honey bees’ brain via oxidative stress. Acute, field-realistic sublethal exposure to tebuconazole decreased the brain’s antioxidant capacity, key antioxidant defense systems, and oxidative degradation and alteration of lipids (fats) in the brain. Thus, this study adds to the scientific literature on the adverse effects of chemical exposure on pollinator health, especially in sublethal concentrations. Degenerating cognitive skills can threaten honey bee survivability, decreasing colony fitness and individual foraging success. Much research attributes the decline of insect pollinators (e.g., commercial and wild bees and monarch butterflies) over the last several decades to the interaction of multiple environmental stressors, from climate change to pesticide use, disease, habitat destruction, and other factors.

Pollinator declines directly affect the environment, society, and the economy. Without pollinators, many plant species, both agricultural and nonagricultural, will decline or cease to exist, as U.S. pollinator declines, particularly among native wild bees, depress crop yields. In turn, the economy will take a hit, since much of the economy (65%) depends upon the strength of the agricultural sector. As the science shows, pesticides are one of the most significant stressors for pollinators. Additionally, the devastating impacts of pesticides on bees and other pollinators and the larger context of what has been called by scientists as the “insect apocalypse.” In a world where habitat loss and fragmentation show no sign of abating, scientists have concluded that the globe cannot afford to continue to subject its critically important wild insects to these combined threats. Therefore, studies like these emphasize the need for improved assessment for environmentally relevant levels of chemical exposure to honey bees.

The study notes, “[R]edox imbalance and oxidative stress-related negative consequences may be factors of crucial importance in the background of neurotoxicity and cognitive impairment observed by the abovementioned research groups in tebuconazole-exposed bees. Therefore, it is vital to understand whether tebuconazole may have a negative impact on the redox homeostasis of honeybees, possibly contributing to the development of further pathological conditions.”

Using adult honey bees, the researchers exposed the bees to acute sublethal, field-realistic concentrations of tebuconazole in high, medium, and low doses. The researchers analyze the fatty acid composition and oxidative factors in the brain of honey bees, including total antioxidant capacity (TAC), state of the glutathione defense system, the activity of glucose-6-phosphate dehydrogenase (G6PDH), superoxide dismutase (SOD), and xanthine oxidase (XO), and the production of malondialdehyde (MDA).

The results show tebuconazole has a profound impact on oxidation in the brain. It decreases antioxidant capacity, reducing the ratio of oxidized glutathione for preventing damage to important cellular components and disrupting antioxidant enzymatic defense systems, inducing lipid (fat) peroxidation (oxidative degeneration of fats) through elevated malondialdehyde levels.  This alters the fatty acid profile in honey bee brains.

The scientific literature demonstrates pesticides’ long history of adverse environmental effects, especially on wildlifebiodiversity, and human health. Most notably, pesticides are immensely harmful to pollinators. Over the last decade and a half, increasing scientific evidence shows a clear connection between the role of pesticides in the decline of honey bees and wild pollinators (e.g., wild bees, butterflies, beetles, birds, bats, etc.). Pollinators’ decline directly affects the environment, society, and the economy Globally, the production of crops dependent on pollinators is worth between $253 and $577 billion yearly. Hence, pesticide use fails to support sustainability goals, decreasing agricultural and economic productivity and social (human/animal) and environmental well-being.

The study emphasizes oxidative stress’ role in pesticide toxicity among nontarget species. An alteration in redox homeostasis has an association with many diseases and neurodegenerative disorders and may be a significant factor in regulating cell growth, senescence, and aging. Tebuconazole is a (tri)azole compound that can directly impact cellular metabolic processes like antioxidation. The chemical also has a history of affecting bee behavior, foraging effectiveness, pollination, learning, and colony development, indicating impact on the brain. Behavioral changes and an overall decrease in cognitive function have a strong correlation with triazole-induced oxidative stress.

Although literature on oxidative stress, neurodegenerative disorders and honey bees is lacking, this study provides evidence that future studies must assess how pesticides impact cognitive function among invaluable insects. Additionally, triazole fungicides can work synergistically with other bee-toxic pesticides, like neonicotinoids (insecticide), amplifying adverse effects on health. In fact, systemic neonicotinoid insecticides put 89% or more of U.S. endangered species at risk. The study attributed pesticide toxicity to the ongoing pollinator crisis, highlighting that more extensive research on triazole-mediated health effects is essential for the conservation of honey bees and endangered pollinators. The researchers say, “[T]he negative impact of tebuconazole on honeybees and contributes to the understanding of potential consequences related to azole exposure on pollinator insects’ health, such as the occurrence of Colony Collapse Disorder (CCD).”

Pollinator protection policies need improvements to safeguard all pollinators and the crops they pollinate. Beyond Pesticides holds that we must move beyond pesticide reduction to organic transition and commit to toxic pesticide elimination in our agricultural system to prevent the crop loss presented in this study. Pesticide elimination can alleviate the effect of these toxic chemicals on humans and wildlife. With EPA failing to take the most basic steps to protect declining pollinators, it is up to concerned residents to engage in state and community action and demand change. Moreover, the government should pass policies that eliminate a broad range of pesticides by promoting organic land management. Habitat in and of itself may assist, but it must be free of pesticides to protect wild pollinator populations.

To protect wild bees and other pollinators, check out what you can do by using pollinator-friendly landscapes and pollinator-friendly seeds, engaging in organic gardening and landscaping, and supporting organic agriculture through purchasing decisions. Learn more about the science and resources behind the adverse effects of pesticides on pollinators and take action against the use of pesticides. Buyinggrowing, and supporting organic will help eliminate the extensive use of pesticides in the environment. Organic land management and regenerative organic agriculture eliminate the need for toxic agricultural pesticides. For more information on the organic choice, see the Beyond Pesticides webpages, Health Benefits of Organic AgricultureLawns and Landscapes, and Parks for a Sustainable Future

Learn more by registering for the virtual 40th National Forum Series, Forging a Future with Nature: The existential challenge to end petrochemical pesticide and fertilizer use, starting on September 14, 2023. Visit our to Forum website.

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Source: Insect Biochemistry and Molecular Biology

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