Pesticides pose long-term threats to honey bees and bumblebees

Photo: Pixabay/kimgreenhalgh90

Bees and bumblebees serve important biodiversity functions as pollinators yet worldwide their numbers have been decreasing as a result of various stresses from heat waves to habitat loss to pesticide use.

New research has zeroed in on the latter threat in Ireland with concerning implications. The scientists behind it have found that honey bees and bumblebees remain exposed for long periods to various chemicals found in two pesticide groups known as fungicides and neonicotinoid insecticides.

For their study the researchers sampled soil for pesticide residues at 12 sites in Ireland. Importantly, they found that after their use most pesticides persist for a long time in the soil from where they can then end up in the pollen of crops visited by bees and bumblebees.

Worse, various pesticides pose threats at various sites that the insects visit. “Crop pollen was only contaminated with fungicides; honey bee pollen was mostly contaminated with fungicides; bumblebee pollen mostly by neonicotinoid insecticides,” the scientists report.

“Taken in combination, these results raise significant concerns about the potential wide-spread exposure to multiple pesticides,” the experts note. “Additionally, some previous studies have shown that when insecticides and fungicides are combined, the results may be more toxic than for each category alone.”

The highest number of chemicals was detected in bumblebee pollen, posing a great threat to these avid pollinators, but bees face their own set of challenges.

“Essentially, this means that using honey bees as a reference for understanding the exposure to different pesticides cannot give a complete picture. What’s true for honey bees doesn’t seem to be true for bumblebees, and we know that both are important for the overall pollination service and for supporting healthy ecosystems,” says Elena Zioga, a PhD candidate at Trinity College Dublin’s School of Natural Sciences who was the first author of the study.

“It is also very worrying that the five neonicotinoids we looked for appeared in bumblebee pollen and not in crop pollen. Some of these pesticides, known to be particularly toxic, had not been applied in the fields we sampled for at least three years. This shows either that they persist for a long time in the field edges, where wildflowers grow, or that bees collected neonicotinoid-contaminated pollen from beyond the sampled fields,” Zioga says.