Jonathan Lundgren, a senior research entomologist with the USDA’s Agriculture Research Service who has spent 11 years with the agency based in Brookings, S.D., said that retaliation and harassment from inside USDA started in April 2014, following media interviews he gave in March of that year regarding some of his research conclusions.

Lundgren’s work has included extensive examination of a class of insecticides known as neonicotinoids, or neonics, which are widely used by U.S. farmers to control pest damage to corn and other crops, helping protect production. The insecticides are sold in forms that both are sprayed on plants or coated on seeds before they are planted. They are also used on plants sold by lawns and garden retailers.

Lundgren is the first to file a formal complaint since questions arose recently about the scientific integrity of research by USDA scientists. The talk has dogged the agency for the last few years and some critics complain that scientific findings on a range of topics are suppressed if they contradict the interests of powerful corporations.

USDA declined to comment about Lundgren’s case or his specific complaints. But in a statement, the agency said it takes the integrity of its scientists’ work seriously.

“We recognize how critical that is to maintaining widespread confidence in our research among the scientific community, policy-makers, and the general public,” the statement said.

Neonicotinoids are a particularly sensitive topic because some scientists have linked them to dramatic declines in honey bee colonies, which help pollinate roughly a quarter of the food consumed annually in the United States.

The agrichemical companies that sell neonic insecticides, such as Bayer AG, BASF, Syngenta AG and others, have said other research shows that neonics are not the problem, and they have been actively lobbying lawmakers and regulators against limiting use of neonics.

Neonics are a key part of a growing global insecticide market projected at roughly $15 billion in revenues.

Lundgren and other scientists have raised questions about both the effectiveness and environmental safety of the insecticides. Research has linked “neonics” to the demise of Monarch butterflies and honey bees, in particular. Two research reports by Lundgren concluded that farmers received no yield benefit at all in using the costly neonic seed treatments.