20
Oct
Glyphosate Based Herbicides and Bee Health: The American Bumble Bee
(Beyond Pesticide, October 20,2022) Exposure to environmentally relevant levels of glyphosate-based herbicides (GBHs) weakens bumblebees’ (Bombus Terrestris) ability to distinguish between colors or fine-color discrimination. According to research published in Science of The Total Environment, a lack of fine-color discrimination skills can threaten bumble bee survivability through impact on 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. In the U.S., an increasing number of pollinators, including the American bumblebee and monarch butterfly, are being added or in consideration for listing under the Endangered Species Act, with specific chemical classes like systemic neonicotinoid insecticides putting 89% or more of U.S. endangered species at risk.
Pollinator decline directly affects 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, limits crop yields. In turn, the economy will take a hit, as much of the economy (65%) depends upon the strength of the agricultural sector. As science shows, pesticides are one of the most significant stressors for pollinators. 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 highlight the need to establish monitoring and conservation frameworks incorporating varying habitats and species to assess fluctuations in biodiversity. The study coauthor and university teacher, Olli Loukola, PhD, of the University of Oulu, Finland, notes, “[T]he results are quite worrying considering the importance of color vision for bumblebees. Even small disturbances in color vision can be catastrophic in terms of foraging and nesting success.”
GBHs are the most common herbicides used globally. Previous studies evaluating chronic glyphosate or GBH exposure assessed the survival, development, physiology, colony thermoregulation, or gut microbiota specific to honey bees. However, very few studies have tested field-realistic exposure to glyphosate honey bees’ cognitive performance, and no studies examined this question in non-honey bee pollinators (e.g., bumble bees). Thus, researchers evaluated the effect GBHs have on bumblebee cognition when exposed to acute levels of environmental (field) realistic doses of these chemicals. To simulate field-realistic exposures of GBH, the researchers provided each bumblebee with 60 percent sugar with or without GBH quinine. A series of learning and memory experiments represented cognition traits as these traits determine the successful foraging and social behavior of insects and their fitness. In the learning phase, bees can choose between a rewarding sucrose solution or an aversive quinine solution in the flowers of 10 different plants. Two days after the learning phase, the bees underwent a memory test with the same setup as in the learning phase, except that each flower contained water. The experiment examined how to control bumblebees (not exposed to GBH) and GBH-exposed bees to distinguish between flowers based on ten different colors when searching for nectar or pollen. Moreover, researchers tested if the cognitive impacts of GBH-exposed bees affect general vision and/or olfactory (odor) senses.
One to several acute exposures to GBHs, similar to field-realistic perspectives, significantly impairs bumble bees’ ability to discriminate between the ten flower colors. During the learning phase, control and GBH-exposed bees display differences in learning rate. Control bees learning rate increased after two sessions, while GBH-exposed bees’ learning rate dropped to zero. Two days after the completion of the learning phase, researchers performed a memory test on both bee groups. The researchers split the control group into two, leaving half without GBH exposure while treating the remaining control bees with GBHs. The results find the second group of control bees performed at the same level as the learning session, while the new group of GBH-exposed bees lost all learning from the previous two days. The study also demonstrates GBH does not affect bumble bees’ ability to discriminate between odors or two spectrally different colors (i.e., yellow, and blue in the experiment). Thus, the results suggest GBHs’ impact on fine-color discrimination among bees obscures the color information of rewarding flowers used in memories for future decisions. The study suggests, “…that acute sublethal exposure to GBH poses a greater threat to pollination-based ecosystem services than previously thought, and that tests for learning and memory should be integrated into pesticide risk assessment.”
Clean air, water, and healthy soils are integral to ecosystem function, interacting between Earth’s four main spheres (i.e., hydrosphere, biosphere, lithosphere, and atmosphere) to support life. However, toxic pesticide residues readily contaminate these spheres, frequently in soils, water (solid and liquid), and the surrounding air at levels exceeding U.S. Environmental Protection Agency (EPA) standards. The scientific literature demonstrates pesticides’ long history of adverse environmental effects, especially on wildlife, biodiversity, 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.) alike. The agricultural industry relies on insect pollinators to aid in plant pollination and crop productivity. 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.
While it is evident that each factor contributing to the decline of the American bumblebee is problematic, including pesticides, parasites, and poor nutrition, pollinators are exposed to multiple stressors at once that act together to increase the risk of bee mortality.
Almost five decades of extensive glyphosate use has put animal, human, and environmental health at risk as the chemical’s ubiquity threatens 93 percent of all U.S. endangered species. Although the direct effect that pesticides have on pollinators is concerning, the indirect impacts that pesticides have on pollinator habitats are equally troublesome. Glyphosate use in mono-crop agriculture and genetically engineered crops can drift onto and destroy adjacent habitats. Habitat destruction results in the loss of species biodiversity and stable ecosystem processes integral to sustainability.
When looking at pesticide exposure, glyphosate represents only one class out of thousands of agrichemicals that pollinators may encounter. Pesticide use poses one of the most significant threats to bumblebees and places their entire life cycle at risk. A 2018 study found that commonly used neonicotinoid insecticides begin to kill off bumblebees during their nest-building phase, as exposure makes it more difficult for a queen to establish a nest. Exposure to neonicotinoids results in bumblebee colonies that are much smaller than colonies not exposed to the systemic insecticide. Moreover, a 2017 study finds that neonicotinoid exposure decreases pollination frequency and results in fewer social interactions. That is likely because neonicotinoids alter bumblebee feeding behavior and degrade the effectiveness of bumblebee’s classic “buzz pollination” process. Research published in 2017 determined that fungicides also play an important role in bumblebee declines by increasing susceptibility to pathogens. Moreover, the U.S. Environmental Protection Agency (EPA) assesses the toxicity of individual active ingredients on bees through various testing methods when regulating pesticides. However, there are no requirements for EPA to test multiple active or inert ingredients to the same degree, despite evidence demonstrating these chemicals harm pollinators.
The study demonstrates acute exposure to GBH during foraging sessions within a recently sprayed area significantly impairs bumblebees’ fine-color discrimination and long-term memory. In the wild, when discriminating between different colored flowers, bees must distinguish between flowers that appear much closer in color than in the 2-color experiment (yellow and blue flower). Thus, the results of the 10-color experiment, noting impacts on fine-color discrimination and long-term memory, represent a more ecologically relevant environmental condition for bee foraging. Although the study suggests impairment of fine-color discrimination and long-term memory may decrease individual and colony fitness, “The relative biological importance of bees’ contrasting color and fine-color discrimination performance, as well as their ability to discriminate between different odors, remains to be revealed in future studies.”
The study concludes, “[O]ur results emphasize the imperative need to direct our collective research focus on the substantial, complicated, and ecologically relevant risk scenarios rather than lethal doses alone. These risks are not limited to agroecosystems because glyphosate residues are near-ubiquitous in wild environments as well, and a vast majority of plant species are animal pollinated. Thus, sublethal consequences of GBHs should be considered not only in future research but also in public discussion, decision making, and development of environmentally friendly pesticides.”
Pollinator protection policies need improvements, not only to safeguard wild pollinators but the crops they pollinate as well. 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 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 effect of pesticides on pollinators and take action against the use of pesticides. Buying, growing, 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 Agriculture, Lawns and Landscapes, and Parks for a Sustainable Future.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Phys.org, Science of The Total Environment
