Pesticides intended to help bees may actually be dangerous to their health

August 9, 2016

Max Carol

Honey bees

Beekeepers often spray hives with pesticides to fight parasites, but these chemicals could have hazardous side effects.

Honey bees (Apis mellifera) are a vital component of global agricultural production, mainly due to their role as pollinators. About one third of the food in our diet benefits directly or indirectly from honey bee pollination, including most fruits, vegetables, and nuts. Unfortunately, worldwide bee populations have been in decline over the past few decades. Poor nutrition, pesticides, and parasites like Varroa mites (Varroa destructor) have wrecked havoc on honey bee colonies around the world.

To combat Varroa mites and other parasites that kill honey bees, beekeepers have been applying special pesticides to beehives. These chemicals are supposed to kill mites and leave bees unharmed, reducing infestations and eventually increasing bee populations. However, a new study published in the journal Frontiers in Microbiology indicates that many of the pesticides commonly used to protect bees may actually damage bacterial communities in their guts, which can have severe effects on bee health.

The study was conducted on several farms in Virginia, where the annual rate of hive loss is over 30%. Researchers from Virginia Tech extracted DNA samples from bees that lived in four different hives across the farms. Each of the first three hives was treated with a different pesticide (tau-fluvalinate, coumaphos, and chlorothalonil), while the fourth hive was left untreated.

DNA analysis revealed that the structures of bacterial communities residing in the guts of honey bees were altered when the bees were exposed to pesticides. Bees treated with chlorothalonil demonstrated the most severe changes in structure, but all three pesticides affected the structure of the honey bee gut microbiome, or the collective genomes of the microorganisms that live in the guts of honey bees. The researchers believe that the changes to structure caused by pesticides could affect bacterial function, making it harder for bees to metabolize sugars and peptides. These processes are vital for maintaining proper honey bee health.

“Although helpful for ridding hives of parasites and pathogens, the chemicals in beekeeper-applied pesticides can be harmful to the bees,” Mark Williams, the lead author of the study, explained in a press release. “Our research suggests that pesticides could specifically impact the microbes that are crucial to honey bee nutrition and health.”

While pesticides have been cited as a major factor in bee colony declines, the pesticides tested in the study are unique as they were applied to hives with the purpose of protecting bees. Often, bees are harmed by pesticides that are not intended to affect them at all. For example, a study published a few weeks ago in the journal Proceedings of the Royal Society B showed that some common pesticides could reduce bee sperm counts by 39%.

The authors of the study believe that further research into the side effects of pesticides will be necessary to protect bee populations. According to their report, “The results of this field-based study suggest the potential for pesticide induced changes to the honey bee gut microbiome, and thus warrant further investigation into whether chlorothalonil or other pesticide exposure can have biologically significant impacts on honey bee function, health, and survival.”



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