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Exposure to streptomycin, an antibiotic used to treat crop diseases in the US, weakens the foraging ability of the common eastern bumblebee (Bombus impatiens), which may have negative implications for plant pollination.

The use of antibiotics for spraying crops has increased exponentially in recent years, with streptomycin predominantly used in the US to control the in apple and pear orchards.

To assess the impact of contact with the drug on a key pollinator, at Emory University in Atlanta, Georgia, and her colleagues fed a group of B. impatiens a diet of sucrose mixed with streptomycin at a concentration of 200 parts per million 鈥� representative of strengths used to spray crops. A control group received sucrose alone. After two days on these diets, the bees were given a series of tests.

Bees exposed to streptomycin took longer to be trained to associate sucrose and water with different coloured strips of card soaked in the liquids. Also, in a 2-hour foraging test in which the bees were tracked by radio tags, they visited fewer sucrose-filled artificial flowers than bees in the control group.

Separate tests showed that individual bees would choose to consume less antibiotic-laced sucrose than sucrose alone, suggesting that nectar tainted with antibiotics could be less attractive.

鈥淲e are conducting follow-up work to see if these behavioural effects are driven by changes in the bee gut microbiome,鈥� says Avila.

鈥淟aboratory studies from other research groups have shown that antibiotics can 鈥� unsurprisingly 鈥� disrupt bee gut microbiomes,鈥� she says, 鈥渁nd work in honeybees and other insects has shown microbiome changes can impact insect behaviour.鈥�

To further investigate how exposure to antibiotics could affect both B. impatiens populations and plant pollination, the researchers are beginning to assess the levels of exposure to the drugs faced by bees in the real world when they are sprayed on crops. The research is being funded by the US Department of Agriculture.

鈥淭he real world implications of this study are concerning. These findings indicate a widely accepted practice can lead to subtle yet severe harm to the bumblebees so important to crop pollination,鈥� says at the Xerces Society for Invertebrate Conservation, a non-profit organisation. 鈥淲hile sometimes bee kills are reported, the 鈥榮ublethal鈥� impacts described in the study are less obvious, but can be just as devastating. Hopefully, this and other similar studies can be a wake-up call.鈥�