Browsing by Subject "Wassersammelverhalten"

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Freisetzung von Neonicotinoiden aus der Saatgutbeizung in Guttation von Kulturpflanzen und deren Auswirkungen auf Honigbienen Apis mellifera L. (Hymenoptera: Apidae)
(2015) Reetz, Jana E.; Zebitz, Claus P. W.
Seed coating with the systemic neonicotinoids clothianidin, imidacloprid, and thiamethoxam was considered environmental justifiable and no side effects on non-target organisms such as honey bees were considered during the registration process as seed coatings. In 2008, sowings with neonicotinoid-coated corn has caused severe damages on honey bee colonies in the upper Rhine Valley, Germany. As a consequence, the seed coating with neonicotinoids in maize and wheat was suspended in Germany in May 2008; since May 2013 there is a temporary ban of the three neonicotinoids by the EU Regulation No. 485/2013. The release of systemic active substances (a.s.) in guttation of seed-coated plants, e.g. winter oilseed rape (WOR, Brassica napus L.), represents a possible contamination source for non-target organisms and could actively be used as a water source by honey bees (Apis mellifera L.). The occurrence of guttation was examined and sampled under field conditions in maize, xtriticale and WOR. The residual analysis of guttation from seed-coated WOR revealed the release of residues up to 130 µg a.s. L-1 in autumn (Reetz et al. 2015). However, even the highest residues in WOR guttation are considerably lower than those in guttation of maize (up to 8,000 µg a.s. L-1) or xtriticale (up to 1,300 µg a.s. L-1; Reetz et al. 2011). In spring, the released residues in WOR guttation are lower than in early autumn (~30 µg a.s. L-1) and continue to decline steadily until flowering. Considerable high amounts of residues have been released by maize (spring crop) over a long period of the crop cycle. Laboratory investigations (according to OECD-Guideline 213) showed that feeding of isolated honey bees with a sugar/guttation-solution from seed-coated WOR leads to a mortality less than 20 % (Wallner et al. 2012), but this way of exposure is not similar to the situation of water foraging honey bees. Observations of water foraging honey bees in the field are nearly impossible. Therefore, honey-sac content of foragers returning to the hive were analysed for residues (Reetz and Wallner 2014). These experiments showed that on the one side the weight of honey sacs is lower during autumn at the same time when high residues in guttation of seed-coated WOR occur than in summer, and on the other side, that the intake of water is increased by the factor of 25 compared to the amount of nectar, which seems to be associated with the absence of nectar sources during autumn (Reetz et al. 2012). There seems to be no exclusive season- or daytime-depending water collecting activity in honey bee colonies in temperate zones. Therefore, the collection of guttation from seed-coated plants by foraging honey bees is likely. However, during summer and the periods of high nectar flows honey bees might gather rather runny nectar as a replacement for water than WOR guttation. Honey bees gathering on WOR guttation were just occasionally observed in a small-patterned landscape, but more frequently in the field site with intensive agriculture and a reduced variety of alternative water sources. HPLC-MS-analysis of honey sacs (n= 204) reveal that residues of thiamethoxam are detectable in 19 % (n= 38) of the honey-sac contents with a range of 0.3 to 0.95 µg a.s. per litre (LOQ= 0.3 µg a.s. L-1; Reetz et al. 2015 accepted). In 12 % (n= 24) of the samples, thiamethoxam could be detected in concentrations below LOQ. Clothianidin and its metabolite TZMU were measured in one sample each (0.5 %) at concentrations below LOQ (clothianidin) and LOD (TZMU), respectively. Based on these experiments, it has been proven that honey bees use guttation of seed-coated WOR as water source in absence of alternative nearby water sources. Thus, during a short period of about a few weeks in autumn, when the highest residues are released in WOR guttation, there might theoretically be a risk for single honey bees. Guttation of xtriticale and WOR is just temporary present in the field, whereas guttation of maize is present in the leaf sheaths during the day due to the funnel function of the maize leaves. Additionally to theses facts, there is a low water demand in honey bee colonies during autumn in contrast to the occurrence of maize guttation, which occurs at the same time when honey bee colonies raise and have an increasing demand of water. The current evaluation of short-term effects of chronic exposure to sublethal concentrations of neonicotinoids in pollen on honey bees at colony level is based on the application of higher concentrations (2 ppb clothianidin; Sandrock et al. 2014) than detected in the honey-sac contents of the water foraging honey bees in this experiment (< 1 µg a.s. L-1; < 1 ppb). Based on these threshold values for side effects by chronic feeding of neonicotinoids, the concentrations of residues measured in the honey sacs of water foraging honey bees seem to have still less potential for side effects on single honey bees or on colony level.