PARIS — An influential European scientific body said on Wednesday that a group of pesticides believed to contribute to mass deaths of honeybees is probably more damaging to ecosystems than previously thought and questioned whether the substances had a place in sustainable agriculture.

The finding could have repercussions on both sides of the Atlantic for the companies that produce the chemicals, which are known as neonicotinoids because of their chemical similarity to nicotine. Global sales of the chemicals reach into the billions of dollars.

The European Commission in 2013 banned the use of three neonicotinoids — clothianidin, imidacloprid and thiamethoxam — on flowering plants after a separate body, the European Food Safety Authority, found that exposure to the chemicals created “high acute risks” to bees.

But the chemicals continue to be employed on an industrial scale in the United States. The Environmental Protection Agency is reviewing their use after President Obama last year established a national Pollinator Health Task Force to help address concerns about so-called colony collapse disorder, a not fully understood phenomenon that has devastated commercial apiaries.