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Risto Raimets defended his doctoral thesis „Effects of synthetic and biological pesticide exposure on honey bees and bumble bees“ on September 26, at Estonian University of Life Sciences. It was investigated whether and in what amounts can pesticide residues be found in bee-keeping products from areas of different agricultural intensity and how the residues affect bees.

"Even though I identified residues of 17 pesticides in the collected samples, there was no correlation between the land use type, plant species and pesticide residues found," Raimets described the results. He pointed out as particularly noteworthy that although rape pollen and honey constituted a significant proportion of the samples collected, it had no correlation with the pesticide residues found.

It appeared that the honey samples contained only low amounts of herbicide residues. "This testifies to the purity and quality of Estonian honey, and encourages to prefer Estonian honey," said Raimets.

Results of the experiments indicated that even at low doses, pesticide residues affect the development of bee queens, for example. For the first time, experiments with queens showed reduction in the toxicity of the mixture of the insecticide taufluvalinate and the fungicide tebuconazole. However, experiments with bumblebees showed that combining other insecticides and fungicides could increase the toxicity of the mixture.

Supervisors of the doctoral thesis are Professor Marika Mänd and Senior Research Fellow Reet Karise, the opponent is Dennis van Engelsdorp (University of Maryland, USA).