Risto Raimets defended a thesis that looked at traces of pesticides in beekeeping products from areas of different agricultural intensity and how they affect bees.

"Even though I found traces of 17 different pesticides in the samples I took, there was no correlation between land use types, species of plants and pesticides," Raimets said.

Rape fields no more contaminated than others

Because rape is among more popular crops cultivated in Estonia and grown using a lot of different plant protection products, one would expect rape to pass more chemicals onto bees. Raimets' pollen and honey samples did not show heavier concentration of pesticides from rape fields.

Raimets' research discovered traces of 17 pesticides after analyzing Estonian bees and beekeeping products. Insecticides were found most often. Not all insecticides come from agriculture as beekeepers also use them to fight the varroa mite.

The doctoral thesis finds that pesticide residue can make its way into beekeeping products from roadsides that have been treated for weeds. Traces of chemicals can also travel with the wind or soil water to end up in plants the bees frequent.

Estonian honey of high quality

Samples collected from beehives found that traces of chemicals were heaviest in pollen and beebread, while pesticides were scarce in brood and honey. Honey samples only contained light concentrations of herbicides. "This speaks to the purity and quality of Estonian honey and should encourage people to prefer domestic products," Raimets said.

Chemical mixtures more dangerous than individual pesticides

The thesis provides vital insights into the problem of bee colonies collapsing: pesticides that build up in wax and are retained there can threaten the development of queens. A fungicide and insecticide often found in Estonian beekeeping products affect the development of queens to a considerable degree. Both chemicals increase queens' weight the effects of which on their health remains unknown.

An earlier University of Life Sciences study revealed that interaction of different pesticides might be more dangerous than individual chemicals, even when used within permitted levels. Raimets' thesis supports these previous conclusions: mixtures of different pesticides are considerably more harmful than individual substances.

Raimets emphasizes that sets of mixtures need to be analyzed individually as their interactions can differ even in case of chemicals belonging to the same group.

While chemical mixtures have similar effects on honeybees and bumblebees, their intensity differs, for example, in terms of dehydration and mortality rates. It also turned out that honey- and bumblebees have become so different in their nature and physiological characteristics that test results cannot be automatically applied to the other species in some cases.

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