Translocation of Neonicotinoid Insecticides From Coated Seeds to Seedling Guttation Drops: A Novel Way of Intoxication for Bees

Abstract

The death of honey bees, Apis mellifera L., and the consequent colony collapse disorder causes major losses in agriculture and plant pollination worldwide. The phenomenon showed increasing rates in the past years, although its causes are still awaiting a clear answer. Although neonicotinoid systemic insecticides used for seed coating of agricultural crops were suspected as possible reason, studies so far have not shown the existence of unquestionable sources capable of delivering directly intoxicating doses in the fields. Guttation is a natural plant phenomenon causing the excretion of xylem fluid at leaf margins. Here, we show that leaf guttation drops of all the corn plants germinated from neonicotinoid-coated seeds contained amounts of insecticide constantly higher than 10 mg/l, with maxima up to 100 mg/l for thiamethoxam and clothianidin, and up to 200 mg/l for imidacloprid. The concentration of neonicotinoids in guttation drops can be near those of active ingredients commonly applied in field sprays for pest control, or even higher. When bees consume guttation drops, collected from plants grown from neonicotinoid-coated seeds, they encounter death within few minutes.

Scientific Opinion on the science behind the development of a risk assessment of Plant Protection Products on bees (Apis mellifera,Bombusspp. and solitary bees)

“…Measurements of high residue levels of some intrinsically highly toxic, systemic insecticides in guttation droplets from different crops were reported by different researchers (Girolami et al, 2009; and triggered research activities on the risks for bees in 2009. Studies have since been conducted on the environmental conditions and factors favoring guttation, the occurrence of guttation in different crops, the frequency of guttation events and residue measurements in guttation droplets in different crops with different active ingredients in different growth stages (Pistorius et al, 2011a).…”

Standard methods for toxicology research inApis mellifera

“…Observations are done at the level of the colony and only individual observations on bees are included insofar as they may affect colony development. In principle, guttation water would not be a major source of exposure given that normally these droplets occur mainly in early plant developmental stages (Girolami et al, 2009;Tapparo et al, 2012). However, the individual geographical and meteorological conditions of each area should be considered to exclude this potential exposure route.…”

Effects of exposure of honey bee colonies to neonicotinoid seed–treated maize crops

“…It was revealed that the sowing of treated maize seed with the use of pneumatic drilling machine pose an additional, considerable routes of pesticide exposure for honey bees. Drift of insecticidal dusts of coated maize seed during sowing results in contamination of the surrounding areas with flowering bee forage plants and may cause high bee mortality (Greatti et al, 2003;Greatti et al, 2006;Bortolotti et al, 2009;Girolami et al, 2009;Pistorius et al, 2009;Marzaro et al, 2011;Georgiadis et al, 2012;Sgolastra et al, 2012). In North America, where at least 94% of the 36 million hectares planted with maize is treated with clothianidin or thiametoxam, those crops are considered a major source of neonicotinoid exposure for bees living near agricultural fields (Krupke et al, 2012).…”