The report, issued Thursday by the Department of Agriculture and the Environmental Protection Agency, blamed a parasitic mite, viruses, bacteria, poor nutrition and genetics as well as pesticides for the rapid decline of honeybees since 2006. It said there was insufficient evidence a certain class of pesticides known as neonicotinoids was a major cause of the colony collapses.
The European Union voted this week for a two-year ban on neonicotinoid pesticides it said were associated with the bees' collapse, The Guardian reported.
The U.S. report said more research was needed to determine the effects of pesticide exposure.
"It is not clear, based on current research, whether pesticide exposure is a major factor associated with U.S. honeybee health declines in general, or specifically affects production of honey or delivery of pollination services," it said.
Environmentalists said the report was a missed opportunity to build a case for action on a neonicotinoids.
"We've got so much research on neonicotinoids now that all point to major impacts on honey bees and other beneficial insects," said Scott Hoffman Black, director of the conservation Xerces Society. "It was fine to lay out the many issues that affect honeybees but I do think they missed an opportunity to really lay out the very potentially negative impacts of neonicotinoids."