Over a period of four weeks, scientists led by Richard Gill exposed colonies of 40 bumblebees to neonicotinoid and pyrethroid, nicotinelike chemicals used to protect various crops from locusts, aphids and other pests. The United Nations estimates that one-third of plant-based foods depend on pollination.

“Chronic exposure … impairs natural foraging behavior and increases worker mortality, leading to significant reductions in brood development and colony success,” the scientists wrote in the report, for the journal Nature.

Exposure to the pesticides “increases the propensity of colonies to fail,” the researchers found. A 2011 UN report estimated that the efforts of bees and other pollinators such as butterflies, beetles and birds are worth 153 billion euros ($200 billion) a year to the human economy, but are in decline in many nations.