Antibiotic Commonly Used in Orchards Slows Cognition of Bumblebees

A new study found that streptomycin, a popular antibiotic sprayed on food crops, negatively impacts the behavior of bumblebees.

The study, funded by a USDA grant and conducted by scientists at Emory University and the University of Washington, showed that streptomycin “slows the cognition of bumblebees and reduces their foraging efficiency.”

With 75 percent of the world’s crops relying on pollinators, the study highlights the importance of how sprays and pesticides impact the species. Similar studies have concluded that exposure to the antibiotic tetracycline and high concentrations of oxytetracycline can also harm bees’ systems. Specifically, the chemicals alter the gut microbiomes of the bumblebees, resulting in a decrease in their immunity to pathogens. They can even slow bees’ ability to learn and forage in managed colonies.

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For this study, bumblebees (Bombus impatiens) from a managed colony were observed in a lab environment. Some of the bees were fed pure sugar water, while others were fed sucrose dosed with streptomycin.

After two days, the bees were put to the test. Researchers laid out yellow-and-blue-colored cardboard strips, with one color soaked in sugar water and the other in just plain water. The bees were observed with the strips until they touched one with their antenna, and scientists counted how long it took the bees to favor the sugar-soaked strips.

According to the findings, “bees fed streptomycin often required roughly three times as many trials to make the association, relative to the other bees.” Also, antibiotic-treated bees displayed more avoidance to both cardboard strips than the other bees.

In another experiment, the bees were outfitted with tiny, ultra-lightweight “back-packs” with radio frequencies that allowed researchers to track the bee’s movements while they navigated rows of artificial flowers. Some of the fake flowers were doused in sugar water, while some had none. The bees that had been exposed to the antibiotic landed on the sugar flowers at a rate of 55 percent, while the control bees found the same flowers at an 87-percent rate.

Berry Brosi, the senior author of the paper, says of the study: “I was surprised at how strong an effect we found of streptomycin on bumblebees in the laboratory experiments. That makes it imperative to learn if we see similar effects in an agricultural setting.”

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Streptomycin, the focus of this experiment, has been used increasingly as part of US agriculture in the past decade. It is commonly sprayed on orchard crops to fight off bacterial diseases such as fire blight and citrus greening. Fire blight turns the blossoms and shoots of pear and apple trees black, as if they’d been scored by flame, and can result in dead trees. Citrus greening has been devastating to citrus trees in the US and results in green, unripe and inedible fruit that falls from trees too early.

Next, scientists will take the experiments into an orchard to study how bees behave among pear trees sprayed with streptomycin. “If a detrimental impact is found on bumblebees,” states the paper, “the researchers hope to provide evidence to support recommendations for methods and policies that may better serve farmers.”