Effects of neonicotinoid dust from maize seed-dressing on honey bees

In Northern Italy from 2000 to 2008, many spring bee mortalities were clearly linked to sowing of maize seeds dressed with insecticides. In the present study, we investigated the effects on honey bees of clothianidin derived from maize seed-dressing (Poncho®) in laboratory (test by indirect contact) and in semi-field conditions. Despite the reduction of dust dispersion due to the application of the best available sowing techniques (pneumatic seeder equipped with deflector, improvement of seed-dressing quality) our results showed negative effects on honey bees at individual level. In semi-field study, no effect was observed at the colony level despite the high bee mortality rate for 2-3 days after dust application. However, we can expect a colony decline and low honey production if this high forager mortality rate lasts for longer than 10 days. Such a situation is possible if the sowing period lasts several days as in the Po Valley, where the landscape is characterized by extended maize cultivation. Specific methodologies to assess the effects of dust have never been included in the official guidelines for the evaluation of side-effects of plant protection products on honey bees. For this reason, suitable and standardized methods for testing in laboratory and in semi-field conditions the effects on honey bees of contaminated dust dispersed during sowing were evaluated.