Dust in the wind – drift of dust containing insecticides – a risk for honey bees (Apis mellifera L.)?
Authors: Georgiadis Pablo , Pistorius Jens , Heimbach Udo 
Published: April 2011

In late April 2008, dust drift containing insecticide resulted in the largest bee poisoning in Germany for 30 years. The reason for these incidents was the contamination of flowering bee forage plants with dust particles abraded from maize seeds treated with Clothianidin recorded in the Upper Rhine Valley, Baden-Wuerttemberg and in parts of Bavaria during sowing of maize.Clothianidin, an insecticidal active substance from the group of neonicotinoids, works as agonist at the nicotinic acetylcholine receptors with broad spectrum of efficacy. Clothianidin is also used as a seed dressing of maize (agent for seed treatment “Poncho Pro®”; 1,.25 mg a.i. Clothianidin./kernel) for the control of the larval stage of the Western corn rootworm (Diabrotica virgifera virgifera LECONTE).Since early 2009, studies on the drift of seed treatment dust in off-crop areas, on residues in neighbouring crops, exposure and effects on honeybees are conducted as a part of the German Diabrotica research programme.In practical drift experiments in 2009 and 2010 the impacts of dust drift on individual bees in wind-permeable wooden cages (direct exposure to dust during sowing) and on bee colonies in semi-field and field trials (exposure to dust during sowing and contaminated pollen and nectar) were examined. In addition, samples of pollen and nectar from foragers and in the hives were taken for residue analysis.As blooming neighbouring crops mustard (2009) and winter oilseed rape (2010) were used, contaminated by seed treatment dust at the sowing of winter oilseed rape seed (Elado® treated seeds from 2008, medium dust abrasion values, 2009) and maize seeds respectively (Poncho Pro ® treated seeds from 2008, high dust abrasion values, 2010). For sowing of maize a pneumatic vacuum operated precision air planter with at least 90% drift reduction by re-equipping technology and for rape a pneumatic seed drill was used. Additional to the cages, petri dishes were set up at different levels and in specific distances from the field edge of the drill area (1, 3, 5, 10 and 20 m) at free cut areas of the neighbouring culture before application. Previously the dishes were prepared for an oral feeding test (once with sugar water smeared fresh mustard leaf and another time with honey layer). Behaviour and mortality of the bees were observed and documented in laboratory for 48 hours.Current results showed no adverse effect on bees and bee colonies at rape sowing in 2009. However, in the maize sowing field trials in 2010 bee mortality was clearly increased.More data on the impact of exposure of dust on colonies were obtained from experimental approaches in tents with selective manual application of practical amounts of insecticide-loaded dust (T1 = 0.5 g a.i. / ha and T2 = 2.0 g a.i. / ha Clothianidin) with particle size less than 300 µm in Phacelia. Both application experiments in 2009 and 2010 show a tendency for higher bee mortality at an application rate of 2.0 g a.i. / ha Clothianidin. A clear assessment of the results is not yet possible as their analytical reports are not fully completed.For 2011, further studies on the impact of seed treatment dust on the population development of bee colonies and potential sublethal effects will be conducted.