There is a worrying reduction in the population of bees worldwide. Because bees are considered as major pollinator of crops, decline in their number threatens global food production and supply.

Now, a new research provides another evidence that the long-term and large-scale decline in bee population could be blamed in part to the use of neonicotinoid insecticides.

In a new study spanning 18 years, researchers looked at wild bees that forage from oilseed rape crops, which are widely treated with neonicotinoids. They found that these insects are three times more likely to experience long-term population decline compared with bees that forage from other sources.

"Using a multi-species dynamic Bayesian occupancy analysis, we find evidence of increased population extinction rates in response to neonicotinoid seed treatment use on oilseed rape," the researchers wrote in their study, which was published in the journal Nature Communications on Aug. 16.

Neonicotinoids are widely used worldwide in a variety of crops to keep away insects that eat through harvests, but they also harm insects that benefit plants. Lab-based studies have shown that this pesticide is also harmful to certain species of bee, particularly commercial honeybees and bumblebees.

The result of the new study offers some of the first evidences that exposure to neonicotinoid can scale up and lead to major damages to bees.

"Prior to this, people had an idea that something might be happening, but no-one had an idea of the scale," said study author Ben Woodcock, from the Natural Environmental Research Council Center for Ecology and Hydrology.

"(Our results show that) it's long-term, it's large scale, and it's many more species than we knew about before."

Until now, most of the studies that looked at the effects of the chemical was limited to short-term and small-scale research. Many of these studies were also performed in laboratory settings and focused on just a few species.

The result of the new study is different and more reliable in that it used 18 years' worth of data and involved more than 60 bee species in England. The research also relied on field data.

"It's nice to see the use of long-term data to look at trends in pesticide impacts over longer time scales," said Dara Stanley, from the National University of Ireland Galway, who was involved in earlier research on the impact of neonicotinoids on bees.

"That is something that has been missing in the debate on bees and pesticides so far, and there have been many calls to look at effects over time."

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