Although researchers believe the measured concentrations of neonicotinoids in the tested honey samples are not enough to harm humans, they warn that "a significant detrimental effect on bees is likely for a substantial proportion of the analyzed samples, as adult bees rely on honey for food, including during periods of overwintering or seasons without blossoming flowers".
Honey Bee on Willow Catkin.
Neonicotinoids are considered to be the world's most widely used class of insecticides.
Researchers from University of Neuchatel in Switzerland tested 198 honey samples for five commonly used neonicotinoids - insecticides that affect the central nervous system of insects.
"The increasingly documented sublethal effects of neonicotinoid pesticides at environmentally relevant concentrations on bees", the researchers note, "include growth disorders, reduced efficiency of the immune system, neurological and cognitive disorders, respiratory and reproductive function, queen survival, foraging efficiency", and decreased homing capacity. "On these contaminated samples, 45 % contained at least two, and 10 % four or five ". The average of these concentrations is known to cause deficits in learning and behavior in honey bees.More news: Iowa State QB Park takes leave from team for medical reasons
The honey of North America was a dismal figure: the samples drawn from the continent were contaminated in 86% of cases, compared with 57 % of those from South America.
Three-quarters of the world's honey contains nerve agent pesticides that pose a potential health hazard to humans, a study suggests. But the pesticides have been controversial, because a number of studies have found that they can hurt pollinators as well as pests.
In 2013, the European Union began a temporary ban on the use of three neonicotinoids on crops visited by bees, and is considering a comprehensive ban on the use of the pesticides in all outdoor fields. The honeys asians, on the other hand, had a contamination rate of 80 %.
"These findings are alarming", said Chris Connolly, an expert in neurobiology from the university of Dundee, author of an article accompanying the publication of the study.
Bumblebees and sweat bees tend to live in smaller hives than honeybees, so just a few foragers can more quickly spread contamination to the whole colony.