The researchers say their findings will help expand knowledge about the influence of pesticides on honey bee health.
A paper on the study, by the National Veterinary Research Institute in Pulawy, Poland, is published in the Journal of Chromatography A.
The researchers, led by Tomasz Kiljanek of the Department of Pharmacology and Toxicology, report how they developed and validated a method for simultaneously detecting up to 200 pesticides and metabolites in honey bees.
Honey bee populations are falling worldwide, including in the US. Without the honey bee, American dinner plates would look quite bare; around one third of the food eaten in the US comes from crops pollinated by honey bees.
One of the reasons honey bees are declining in Europe and the US is a condition called colony collapse disorder (CCD).
While nobody has yet fully explained the causes and mechanisms of CCD, scientists generally agree several factors could be involved and working together - pesticides being one of them.
Because some studies have linked them to bee deaths, the European Union have already banned the use of neonicotinoid pesticides.
However, the problem of declining bee populations is not going to be solved by banning one pesticide, say the authors of the new study. With so many pesticides in current use, it is very difficult to work out which ones could be harming bees. Harm can also arise from combined effects, or accumulation over time.
The need for a test that detects several pesticides simultaneously
Even at very low levels, because of interaction effects, it may be possible for pesticides to weaken bees' defense systems and make them vulnerable to parasites and viruses, says Kiljanek.
Thus, note the researchers, in order to find out more about them, we need more sensitive and reliable ways of detecting as many pesticides in bees as possible. Kiljanek explains:
"We wanted to develop a test for a large number of pesticides currently approved for use in the European Union to see what is poisoning the bees."
He and his colleagues developed their method for detecting pesticides in honey bees from a system called QuEChERS, which is currently used to detect pesticides in food.
The system uses a combination of chromatography and mass spectrometry. Chromatography is a technique that separates the various ingredients of a mixture; mass spectrometry is a method that identifies and quantifies molecules by measuring how they behave in a magnetic field.
'Expand knowledge about impact of pesticides on honey bees'
To develop the method for use in honey bees, the researchers faced the challenge of how to prepare a sample for analysis without it containing compounds from the bees themselves.
The insect's body is complex, and samples have to be cleaned up to remove compounds like beeswax, chitin and proteins. The researchers note how the agents used in the clean up can also leave impurities.
However, eventually, the researchers developed and validated the method and found they could test poisoned bees for up to 200 different pesticides at the same time - plus several metabolites (compounds produced as a result of the bees digesting the chemicals). Ninety-eight percent of the compounds tested for are approved for pesticide use in the European Union.
The study paper describes how the researchers used the new method to investigate over 70 honey bee poisoning incidents and found 57 different pesticides present in the bees.
Kiljanek says the finding is just the beginning of a long process to solve the toxic puzzle of how pesticides impact the health of honey bees. He concludes:
"Our results will help expand our knowledge about the influence of pesticides on honey bee health, and will provide important information for other researchers to better assess the risk connected with the mix of current used pesticides."
In October 2015, Medical News Today learned how researchers found diesel exhaust alters half of floral scents that honey bees use to find flowers, and they suggest the effect could be contributing to decline in bee populations.