Assessment of the environmental exposure of honey bees to neonicotinoid insecticides coming from corn coated seeds.

Colony Collapse Disorder (CCD), the sudden loss of most honeybees of the hive represents a worldwide crisis. The consequent losses in crops productivity and plant pollination constitute a major emergency from both economical and ecological standpoints. Although on the causes of CCD several hypothesis have been advanced (parasitic mites, viruses, insecticides, etc.) up to the present no one has been clearly supported by experimental results. In several countries the phenomenon is mainly observed in the period of corn sowing (spring), that generally occurs using corn seeds coated with specific insecticides. As a consequence, seed-coating neonicotinoid insecticides that are extensively utilized in the corn crops have been blamed for CCD. In this connection, two possible ways of environmental exposure and intoxication of honeybees to neonicotinoid insecticides were studied: 1) the atmospheric emission of particulate matter containing the insecticide by the sowing-machine and 2) the translocation of the systemic neonicotinoids from the coated seed to guttation drops of young corn plants. Quantitative measurements conducted both in laboratory and in the field demonstrated that both mechanisms of environmental diffusion of neonicotinoids can produce high exposure levels for bees, with lethal effects compatible with CCD phenomenon: the death manifests within few minutes if bees consume guttation drops or within few hours if they are exposed to particulate matter produced by the sowing machine.