Pesticide Combinations Bad for Honey Bees

Pesticides might be worse for bees than we thought

Combos of agrichemicals pose compounding risks for pollinators.



Cocktails of agricultural chemicals may have a synergistic effect on bee mortality. Pixabay

The plight of pollinators is growing more visible than ever before. Increasingly, scientists are documenting the decline of bees and butterflies, evidence that the loud hum of buzzing insects on many landscapes is turning to a whisper.

For bees, the threats are numerous, including habitat loss, climate change, and intensive agriculture. As fields of flowering plants are converted to roads and row crops, sources of food for wild pollinators dwindle. And when insects forage in farms, they suffer from poor nutrition due to a lack of diverse food sources and become exposed to agricultural chemicals. Honey bees—a managed, non-native species in the US—are transported into many farms to provide pollination, but still face threats from poor nutrition, pests, and pathogens.

A new analysis in the journal Nature shows that some of these threats, when put together, kill more bees than the combination of each threat alone. It turns out, cocktails of agricultural chemicals may have a synergistic effect on bee mortality. In other words, more bees die than would have if the effects of the chemicals simply added to each other.

The authors of the paper analyzed 90 studies that in total documented 356 effects from interacting bee stressors, such as combinations of chemicals, nutritional problems, and parasites. Each study included at least two factors harming bees. They categorized whether the stressors negated each other, added to each other, or compounded to cause extra damage— compounding would indicate a synergistic effect. For example, if one pesticide used alone caused 10 percent of bees to die, and another pesticide killed 15 percent, the two combined would have a synergistic effect if more than 25 percent of bees died.

Across the studies, the researchers repeatedly found that when bees were exposed to multiple agrichemicals, the combination had a synergistic effect on mortality. Meanwhile, combos of other stressors, like parasites and nutrition, tended to have effects that just added together.

Its still unclear why pesticides would have such an effect. In the analysis, the bee stressors didn’t have synergistic effects on non-lethal health measures, like colony growth rates. In other research, however, scientists have found that certain pesticides can weaken a bee’s immune system,…….


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