By Carey Gillam

(Reuters) - A type of insecticide under scrutiny by the White House because of fears about its impact on honey bees has been found in more than half of streams sampled across the United States, according to a study by government researchers published Tuesday.

The study, published in Environmental Chemistry and conducted by U.S. Geological Survey researchers, found that five types of insecticides that are known as neonicotinoids were present in varying degrees in 149 samples taken from 48 streams.

At least one type was detected in 63 percent of the samples collected, USGS researcher Michael Focazio said. The samples included many waterways through the Midwest and Southeast. Concentration levels varied.

Over the last few years evidence has mounted that links the use of neonics, as they are known, to widespread die-offs of honey bees needed to pollinate crops. There are also fears the insecticides are harming other pollinators.

Neonicotinoids, chemically similar to nicotine, are one of the fastest growing classes of insecticides worldwide and are used both in agricultural and urban settings. They are popular with farmers and are often used to coat seeds before they are planted.

The study represents the first national-scale investigation of the environmental occurrence of neonicotinoid insecticides in agricultural and urban settings, the USGS said. The research spanned 24 states as well as Puerto Rico.

“In the study, neonicotinoids occurred throughout the year in urban streams while pulses of neonicotinoids were typical in agricultural streams during crop planting season,” said USGS research chemist Michelle Hladik, report’s lead author said in a statement.

Neonics and their impact on the environment have been a topic of debate in Washington lately.

The U.S. Environmental Protection Agency in May proposed a rule that would create temporary pesticide-free zones to protect commercial honeybees.

The restrictions are aimed at protecting honeybees, which pollinate plants that produce roughly a quarter of the food consumed by Americans. Losses of managed honeybee colonies hit 42.1 percent from April 2014 through April 2015, up from 34.2 percent for 2013-2014, and the second-highest annual loss to date, according to the U.S. Department of Agriculture.

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Beekeepers, environmental groups and some scientists say it is the neonics that are harming the bees.

Agrichemical companies including Bayer and Syngenta disagree, and instead blame mite infestations and other factors.

The White House has formed a task force to study the issue.

(Reporting by Carey Gillam; Editing by Steve Orlofsky)