Antibiotics used on food crops affect bumblebee behavior, lab study finds

The study focused on streptomycin, an antibiotic that has been increasingly used in U.

"No one has studied the potential effects of broadcast spraying of antibiotics on pollinators in agriculture, despite their widespread use," said Laura Avila, co-first author of the paper and a postdoctoral researcher in Emory's Department of Biology.

The current study is based on laboratory experiments using the upper limit of bumblebees' dietary exposure to streptomycin

"This paper is a first step toward understanding whether the use of streptomycin on food crops can cause damage to pollinators that benefit agriculture," said Berry Brosi, senior author of the paper

With funding from the USDA, the researchers will now conduct field studies in orchards sprayed with streptomycin

"Our food production, farmer livelihoods and pollinator health are all intertwined," said Brossi

Based on the available evidence, the researchers hypothesized that the negative effects of streptomycin on bumblebees seen in laboratory experiments may be due to disruption of the insect's microbiome

"We know that antibiotics kill both beneficial microbes and pathogens," Avila said

Avila is a member of Nicole Gerardo's lab

The number of antibiotics sprayed on U.

Avila, who grew up in a coffee-producing region in Costa Rica, said: "I saw how hard it was to grow coffee for a living and how expensive and difficult it was to control pests and diseases

Her family farm is bordered by large virgin forests

75% of the world's food crops depend on at least one of more than 100,000 pollinators, including 20,000 species of bees, as well as other insects and vertebrates such as birds and bats

Previous research has shown that the antibiotic tetracycline, used to treat pathogens in managed hives, can alter the gut microbiota of insects and indirectly increase susceptibility and mortality to pathogens

In the paper, the researchers conducted laboratory experiments on managed bumblebees (Bombus impatiens) to test the effects of high dietary exposure to streptomycin

After two days of dieting, the bees saw cardboard strips of different colors - one yellow and the other blue

The researchers measured the number of trials the bees showed a preference for the sucrose-filled ribbon
.
Bees fed streptomycin typically required about three times as many trials to draw this association compared to other bees
.
Bees on antibiotics were also more likely to exhibit avoidance behaviors to either stimulus
.

Those bees that passed the training threshold were given a short-term memory test five minutes later
.
Give each bee two cardboard strips at the same time and let them choose one
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Streptomycin-injected bees selected about 55% of the sucrose reward, while those not injected with streptomycin selected nearly 87% of the sucrose reward
.

To assess their foraging abilities, the researchers conducted experiments in a foraging chamber with experimental artificial flowers and sucrose or plain water
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The flowers are either blue or yellow, but all the same size and shape
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Each bee is equipped with a tiny, ultra-light radio frequency identification "backpack" to monitor their movements in the artificial flower, and each bee is equipped with a short-range antenna and tracking system
.

The results of the computer analysis showed that the antibiotic-exposed bees visited far fewer flowers with higher sucrose values ​​than the control group
.

In the spring, Avila and Brosi will conduct field studies to determine whether streptomycin in pear orchards affects bumblebees
.

"In laboratory experiments, we found that streptomycin had such a large effect on bumblebees, which surprised me," Brosi said
.
"This made it imperative that we see whether we would see a similar effect in an agricultural setting.

.
"

If field studies identify the harmful effects of agricultural spraying of streptomycin on bumblebees, the timing, amount of antibiotic application and possible antibiotic replacements could be potential mitigations, the researchers noted
.

Journal Reference :

1. Laura Avila, Elizabeth Dunne, David Hofmann, Berry J.
   Brosi.
   Upper-limit agricultural dietary exposure to streptomycin in the laboratory reduces learning and foraging in bumblebees .
   Proceedings of the Royal Society B: Biological Sciences , 2022; 289 (1968) DOI: 10.
   1098/rspb.
   2021.
   2514