Impact of use of neonicotinoid insecticides on honey bees in the cultivation on spring oilseed crops in Finland. Interim report

摘要

The Neomehi project is studying how neonicotinoid-based plant protection products used in the cultivation of oilseed rape and turnip rape affect honey bees in Finnish oilseed cultivation. The interim report brings together the main results of the first growing season.The experimental protocol included four trial fields where spring turnip rape was cultivated. Each trial field was treated in a different way with neonicotinoid insecticides: without neonicotinoids, foliar spraying with neonicotinoids (thiacloprid) against pollen beetles and/or seed treatment with neonicotinoids (thiametoxam) against flea beetles. The plant density and crop growth was determined in the trial fields. The number of honey bees and other pollinators was assessed with the applied line transect method during the growing season. Five test bee hives were located at the edge of each trial field. The condition of the bee hives was checked and the amount of bees and brood was counted 4-5 times during the summer season. Census was done also in autumn and in spring to get overwintering data. Bees and bee hive products from all test bee hives of the trial fields were analysed for residues of neonicotinoids. In addition, residues were analysed from samples collected as a survey from forty other bee hives in South-West Finland. Half of those bee hives were located close to oilseed cultivation and the other half far from oilseed cultivation.The crop growth was normal in three of the trial fields. In one trial field (seed treatment with neonicotinoids) the crop growth suffered probably because of too much varied drilling depth. According to the main results of the counting of pollinators, the number of honey bees in the trial fields was high when the crop growth was good and lower when crop growth was poor. In the field which was treated with foliar spraying with a neonicotinoid (thiacloprid) the number of honey bees decreased after the treatment. However, the number of honey bees clearly increased 2-3 days after the foliar treatment.The results of the first growing season did not show, that the use of neonicotinoids affects the success of bee colonies, which were located at the edge of the trial fields. Both the adult and the brood population dynamic curves showed typical levels and shape of bee and brood population development. The average range of food consumption of the bees during overwintering and the overwintering index (the relation of the number of adult bees in spring compared to the number of adult bees in the beginning of overwintering) showed also typical levels compared to normal bee colonies in South-West Finland. Two bee hives lost their queen during fall and winter. One of those hives was located in the field without use of neonicorinoids and the other in the field in which a seed treatment neonicotinoid was used. The winterlosses of the test bee colonies did not differ from the average winter losses (7 %) in the South-West of Finland.The results of the residue studies showed that residues of neonicotinoids migrate with pollen and nectar into bee hives. The total residue levels of seed treatment neonicotinoids, thiametoxam and chlothianide, were at such a low level, that acute harm to bees is unlikely. However, the residue levels, especially in nectar, resulted in an estimated exposure which is close to the chronic and acute sublethal risk limits presented in literature. Therefore, that kind of risk cannot fully be excluded. The neonicotinoid (thiacloprid) used as a foliar spray resulted in higher residue levels in certain samples than the seed treatment neonicotinoids, and on the other hand in higher estimated exposures. However, the toxicity of the neonicotinoids used in foliar sprayings is only a hundredth of the toxicity of the ones used in seed treatmentand therefore the exposure is estimated to be clearly below the risk limits.The Neomehi project continued with the new field experiments in this summer. Final report based onwider research data will be published in 2015.