(Beyond Pesticides, July 28, 2016) Led by the Institute of Bee Health at the University of Bern, new research finds evidence that two commonly used neonicotinoid (neonic) insecticides have a significant adverse effect on the reproductive ability of male honey bees (drones) and queen bees in managed and wild colonies. The study, Neonicotinoid insecticides can serve as inadvertent insect contraceptives, published in Royal Society Journal Proceedings B, focuses on the differences in lifespan and viability of sperm throughout exposed and unexposed drones.
Since 2006, honey bees and other pollinators in the U.S. and throughout the world have incurred ongoing and rapid population declines from hive abandonment and bee die-off in a phenomenon known as colony collapse disorder (CCD). Neonicotinoids, such as imidacloprid, thiamethoxam and clothianidin, have been found by a growing body of scientific literature to be linked to the CCD phenomenon and pollinator decline in general. While science has become increasingly clear that these pesticides play a critical role in contributing to the ongoing decline of bee health, this is one of the first to look at how these chemicals specifically effect the fertility of male honeybees.
In the study, scientists randomly assigned honeybee colonies consisting of drones and workers (non-reproductive female bees) to either a control treatment or an insecticide treatment consisting of thiamethoxam and clothianidin. The colonies were exposed to these neonics at “field-realistic concentrations found in plant pollen.” Drones were assessed for their sperm quantity and viability once they reached sexual maturity, typically around 9-14 days old. When compared, the test drones yielded 39 percent less living sperm than the control group. These drones also had a significant difference in sperm viability, with the insecticide exposed drones having anywhere from 8 to 11.3 percent lower sperm viability than the control drones.
The reproductive ability of male honey bees helps ensure the overall health of the colony. Being able to successfully mate with the queen bee, an essential part of a drone’s role, relies on the health of their sperm.
“The process of the queen’s mating flight is a one-time thing so it’s really important that she collects plenty of quality sperm, if not, then worker bees in the hive will quickly sense that the queen is ineffective and kill her. We like to call it ”˜game of drones,’” said lead researcher Lars Straub, a Ph.D. student at the University of Bern, to New Scientist.
The sperm that the queen honey bee collects from different drones provides genetic diversity within a colony, helping to protect the hive from the impacts of disease, parasitism, and different environmental changes.
Replacing the queen honey bee can only be done successfully during certain periods of the year and, because of this, colony growth significantly slows down after losing a queen, or it stops altogether. In 2015, study co-author Geoffrey Williams, MD, Ph.D, and senior bee researcher at the University of Bern led another study with an international team of researchers to prove how neonicotinoid exposure results in profound negative impacts to the health of honey bee queens. This study, Neonicotinoid pesticides severely affect honey bee queens, found that queen bees exposed to neonics are more likely to not lay worker eggs, a key indicator of queen health and mating success. In light of this, it may be inferred that individual bee mortality due to neonicotinoid insecticides results in an adverse positive feedback response from the queen that causes detrimental effects on the long-term success of the colony.
The potential link brought up between colony mortality and health of the queen bee caused researchers in the most recent study to point out the urgent need for further investigation into the matter.
The results in the new study demonstrate that exposure to neonicotinoids also significantly reduces the lifespan of drones. During the study, researchers found that the exposed drones had a mortality rate almost double that of the control drones. Considering how long it takes male honeybees to reach sexual maturity, a decrease in longevity could potentially deny neonicotinoid-exposed drones even the chance to mate with the queen bee.
This new study comes on the heels of another study published earlier this year in PLOS One that reported a high rate of U.S. honey bee colony decline coinciding with queen failure linked to drones’ dead sperm. “Queen failure is a big problem and this helps explain it,” said U.S. Department of Agriculture bee scientist Jeff Pettis, Ph.D. in an interview with the Associated Press. Dr. Pettis was not a contributor to the new study, but was lead author of the PLOS study on queen health earlier this year. “It’s not the queens themselves, it’s the drones. It’s significant,” he said.
This new study provides even more weight to the scientific evidence that neonicotinoids play a critical role in the ongoing decline of bees and other pollinators. A USDA funded study published in July 2013 found that exposure to the vast array of chemical combinations found in honey bee hives can weaken bees’ immune systems, increasing their susceptibility to parasites and other pathogens. A 2015 study defined a linear relationship between neonicotinoids and the decline in insect pollinators due to brain dysfunction. With this impact, although bumblebees are unlikely to die, they are likely to encounter difficulty with their learning and memory. Exposed bees will have greater difficulty, for instance, in recognizing the smell of a flower, or how to navigate back to their colony.
Neonicotinoids affect the central nervous system of insects, resulting in paralysis and eventual death. These pesticides have consistently been implicated as a key contributor in pollinator declines, not only through immediate bee deaths, but also through sublethal exposure that causes changes in bee reproduction, navigation, and foraging. Pesticide exposure can impair both detoxification mechanisms and immune responses, rendering bees more susceptible to viruses, parasites, and other diseases, and leading to devastating bee losses.
In light of the shortcomings of federal action to protect these beneficial organisms, it is left up to advocates and consumers to ensure that we provide safe havens for pollinators by creating pesticide-free habitat and educating others to do the same. Take action by calling on EPA to suspend neonicotinoids now. You can also 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.