Field Trial for Evaluating the Effects on Honeybees of Corn Sown Using Cruiser Ò and Celest xl Ò Treated Seeds Paolo Tremolada • Marta Mazzoleni • Francesco Saliu • Mario Colombo • Marco Vighi Received: 12 April 2010 / Accepted: 8 July 2010 / Published online: 24 July 2010 Ó Springer Science+Business Media, LLC 2010 Abstract A first field study was conducted to investigate the possible adverse effects that seeds dressed with neon- icotinoid insecticides pose to honeybees during sowing. It was observed that in the exposure hives bee mortality increased on the day of sowing and that the number of foraging bees decreased the days after the sowing. The corn sowing posed a significant threat to honeybees, with thia- methoxam being the most probable toxic agent. A theo- retical contact exposure was calculated for a bee when flying over the sown fields, revealing a dose of 9.2 ng bee -1 close to the contact LD 50 of thiamethoxam. Keywords Neonicotinoid insecticides Á Honeybees ’health Á Pesticide exposure Á Colony collapse disorder Since the late 90s in the US and in Europe widespread events of a winter-spring honey bee disappearance were registered (vanEngelsdorp et al. 2007; Laszlo 2008), and attributed to a complex pathology of honeybee called Colony Collapse Disorder (CCD) (Hileman 2007). Many causes were considered: pathogens (Ribiere et al. 2008; Higes et al. 2009), environmental stresses, including cli- mate change, (Le Conte and Navajas 2008) and pesticides (Decourtye et al. 2004; Johnson et al. 2009). Of the pesticides, great attention was placed on neoni- cotinoid insecticides, such as acetamiprid, imidacloprid, thiacloprid and thiamethoxam, as these all act on the insect nicotinic (acetylcholine) receptor (nAChR) (Buckingham et al. 1997). Iwasa et al. (2004) revealed that the nitro- substituted compounds were the most toxic (LD 50 values of 18 ng/bee for imidacloprid, 22 ng for clothianidin, 30 ng for thiamethoxam, 75 ng for dinotefuran and 138 ng for nitenpyram) in comparison to the cyano-substituted chemicals (LD 50 values of 7.1 and 14.6 lg/bee for ace- tamiprid and thiacloprid, respectively). Neonicotinoid insecticides are used in agriculture for soil and foliar treatment and as a seed dressing in many crops, such as corn and sunflower. When used as a seed dressing, neonicotinoid insecticides can effect pollinating insects as powder dispersion during the sowing procedures (Greatti et al. 2003, 2006). These authors demonstrated that pesticide contaminated powders are being dispersed to air, during sowing operations when pesticide-dressed seed was used. The pesticide containing powders can subsequently deposit on local soil and vegetation, posing an exposure risk to foraging honey bees and other pollinating insects. As to date there have been very few field investigations conducted on field scale to establishing the science behind CCD (Iwasa et al. 2004). In order to investigate this issue, this research focuses on the possible adverse effects on honeybees of a corn sown using commercial seeds dressed with Cruiser Ò and Celest xl Ò (two common commercial products containing the neonicotinoid insecticide thiametoxam and the fungicides fludioxonil and metalaxyl-M as active ingredients, respectively). P. Tremolada (&) Á M. Mazzoleni Department of Biology, University of Milan, Via Celoria 26, 20133 Milan, Italy e-mail: paolo.tremolada@unimi.it F. Saliu Á M. Vighi Department of Landscape and Environmental Sciences, University of Milano-Bicocca, Piazza Della Scienza, 1, Milan 20126, Italy M. Colombo Department of Protection of Urban and Agri-Food Systems and of Biodiversity Valorisation, University of Milan, Via Celoria, 2, Milan 20133, Italy 123 Bull Environ Contam Toxicol (2010) 85:229–234 DOI 10.1007/s00128-010-0066-1