(Beyond Pesticides, May 3, 2017) Last week, researchers at the University of California San Diego revealed the first ever link between the use of neonicotinoid pesticides and the ability of bees to fly. Published in Scientific Reports, the study, “A common neonicotinoid pesticide, thiamethoxam, impairs honey bee flight ability,” builds on previous findings that neonicotinoid use interferes with bees’ ability to navigate, and concludes that exposure to thiamethoxam affects honey bee flight patterns as well as their physical ability to fly in ways that may be detrimental to their survival. The study is the latest in a growing body of science linking pesticide use to honey bee declines, raising concerns about overall honey bee health and longevity in the face of continued neonicotinoid use.
According to the study, both acute and chronic exposure to thiamethoxam revealed significant alterations of the ability of bees to fly -affecting flight distances, duration of flights, and flight velocity. Researchers noted significant differences in bee behavior based on short versus long term exposure, which they summarized as having an “excitatory short-term effect and a depressive longer-term effect” on the bees’ ability to fly. This means that when bees were exposed to thiamethoxam for a short, acute period of time, their average flight times and flight distances increased dramatically, by an average of 78% and 72%, respectively. In contrast, when the bees were subjected to chronic exposure patterns, it lead to a significant decrease in overall flight duration, distance, and velocity. To reveal these findings, researchers used sublethal exposure levels designed to mimic the amount of pesticide residue bees would likely come into contact with in agricultural fields.
Researchers note that increased flight distances following acute exposure to thiamethoxam offers no benefits to bees, as other studies have revealed thiamethoxam and other neonicotinoids cause flight disorientation and impaired navigation. Therefore, they opine that if these exposed bees are flying greater distances while disoriented from pesticide exposure, it may actually reduce their ability to fly home, negatively impacting overall hive health. On the same note chronic exposure, which reduced bee flight distance by 56%, also poses risks to bees, as it reduces their overall forage area. Additionally, researchers hypothesize that chronic exposure to thiamethoxam may also impact the physical ability of bees to fly by lowering their body temperature, requiring more energy to use the muscles required for flight. Based on these results, researchers predict that bees who experience chronic exposure overall a few days will “fly more slowly and in a reduced area.” Moreover, they believe that the chemically induced changes in their natural behavior patterns will “reduce the pollinator service provided to plants, nectar and pollen collection for the colony, and the nutritional biodiversity of collected pollen for the colony.”
“Our results provide the first demonstration that field-realistic exposure to this pesticide alone, in otherwise healthy colonies, can alter the ability of bees to fly, specifically impairing flight distance, duration and velocity” said Simone Tosi, a postdoctoral researcher and author of the study. Dr. Tosi continued, “Honey bee survival depends on its ability to fly, because that’s the only way they can collect food. Their flight ability is also crucial to guarantee crop and wild plant pollination.”
“Bees that fly more erratically for greater distances may decrease their probability of returning home,” said James Nieh, a professor in UC San Diego’s Division of Biological Sciences and coauthor of the study. Dr. Nieh said, “This pesticide does not normally kill bees immediately. It has a more subtle effect.” He continued, “The honey bee is a highly social organism, so the behavior of thousands of bees are essential for the survival of the colony. We’ve shown that a sub-lethal dose may lead to a lethal effect on the entire colony.”
Thiamethoxam is a neonicotinoid pesticide used on many common crops within the United States, including corn, soybeans, and cotton. Systemic neonicotinoid pesticides, the class of pesticides thiamethoxam belongs to, move through the plants vascular system and are expressed through pollen, nectar, and guttation droplets. These pesticides, which in addition to thiamethoxam include imidacloprid, dinotefuran, and clothianidin, have been found by a growing body of scientific literature to be linked to pollinator decline in general. Neonicotinoids are associated with decreased foraging and navigational ability, as well as increased vulnerability to pathogens and parasites as a result of suppressed bee immune systems.
In its most recent failure to address the harms posed to pollinators by neonicotinoids, the U.S. Environmental Protection Agency (EPA) released major risk assessment documents on pollinator exposure to bee-toxic neonicotinoid insecticides, finding no significant risks, despite the large and continually expanding body of science identifying the pesticides’ hazards. In the documents, EPA identifies risks posed to bees by several neonicotinoid insecticides, but suggested that no restriction on uses are imminent. This is just one example of EPA not taking action to protect bees and other pollinators. In 2016, EPA released the long-awaited preliminary honey bee risk assessment for imidacloprid, one of the most widely used pesticides linked to severely declining honey bee populations, and confirmed harmful residues of the chemical in crops where the pollinators forage, including citrus and other crops. However, although EPA’s assessment confirms bees’ widespread and sustained exposure to the highly toxic and persistent chemical through poisoned pollen and nectar, the document fails to address risks posed to wild bees and widespread exposure through soil and water.
In light of the shortcomings of federal action to protect these beneficial organisms, it is left up to us to ensure that we provide safe havens for pollinators by creating pesticide-free habitat and educating others to do the same. You can declare your garden, yard, park or other space as pesticide-free and pollinator friendly. It does not matter how large or small your pledge is, as long as you contribute to the creation of safe pollinator habitat. Sign the pledge today. Need ideas on creating the perfect pollinator habitat? The Bee Protective Habitat Guide can tell you which native plants are right for your region. For more information on what you can do, visit our BEE Protective page.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.