Scientists have found that two types of chemicals called neonicotinoids and coumaphos are interfering with the insect's ability to learn and remember.
Experiments revealed that exposure was also lowering brain activity, especially when the two pesticides were used in combination.
The research is detailed in two papers inNature Communications and the Journal of Experimental Biology.
But a company that makes the substances said laboratory-based studies did not always apply to bees in the wild.
And another report, published by the Defra's Food and Environment Research Agency (Fera), concluded that there was no link between bee health and exposure to neonicotinoids.
The government agency carried out a study looking at bumblebees living on the edges of fields treated with the chemicals.
Falling numbers
Honey bees around the world are facing an uncertain future.
They have been hit with a host of diseases, losses of habitat, and in the US the mysterious Colony Collapse Disorder has caused numbers to plummet.
