As bee colonies continue to collapse worldwide, a team of European researchers has found that poisoned bees carry a lethal cocktail of dozens of pesticides.

“It is the broadest spectrum of pesticides and their metabolites till now detected in honeybees,” according to the study, which appeared in a recent issue of the Journal of Chromatography A.

Bees are among the world’s most important crop pollinators, responsible for roughly one in three mouthfuls of food grown in the United States alone.

A February report from the United Nations Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services warned that human activities are putting 40 percent of invertebrate species—which include bees, along with 16 percent of vertebrate pollinators—at risk of extinction. The pressure on pollinators could endanger 75 percent of the world’s food supply, the report stated.

The findings are an important step toward pinning down which pesticides and chemical interactions may be causing bee colonies to collapse, according to toxicologist Tomasz Kiljanek of the National Veterinary Research Institute in Poland, who led the study.

Colony collapse rates have surpassed 30 percent in Europe, Kiljanek and his colleagues noted in the study, and are higher than 40 percent in the United States.

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“Even at very low levels, pesticides can weaken bees’ defense systems, allowing parasites or viruses to kill the colony,” Kiljanek said in a statement. “Our results will help expand our knowledge about the influence of pesticides on honeybee health and will provide important information for other researchers to better assess the risk connected with the mix of current used pesticides.”

Kiljanek and his colleagues adapted an analysis method called QuEChERS, typically used to detect pesticide residues in food, to test 74 samples of poisoned bees for 200 pesticides. The samples came from different regions of Poland.

The testing found residues from 57 different pesticides—nearly all legal for use in the European Union—in the poisoned bees. Only one sample was pesticide-free, while the rest showed exposure to an average of four pesticides. The most contaminated sample contained residues from 13 pesticides.

The pesticide chlorpyrifos topped the list with 38 detections, followed by dimethoate at 30.

Clothianidin, a neonicotinoid, was found in 22 samples. The European Union banned clothianidin, along with the neonics imidacloprid and thiamethoxam, in 2013 because of their risks to bees.

The United States has not banned neonicotinoids, although in January the Environmental Protection Agency linked one neonic, imidacloprid, to bee deaths.

Last year, a Department of Agriculture scientist, Jonathan Lundgren, charged that the department had suppressed evidence of a link between neonics and bee die-offs.

This post has been revised to reflect the following correction:

Correction March 14, 2016: An earlier version of this article incorrectly summarized the status of the European Union’s ban on neonicotinoid pesticides. The ban applies to the pesticides clothianidin, imidacloprid, and thiamethoxam and remains in effect.