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.

Losses of honeybees have been reported in Italy concurrent with the sowing of corn coated with neonicotinoids using a pneumatic drilling machine. Being unconvinced that solid particles containing systemic insecticide, falling on the vegetation surrounding the sown area, could poison bees foraging on contaminated nectar and pollen, the effect of direct aerial powdering was tested on foragers in free flight near the drilling machine. Bees were conditioned to visit a dispenser of sugar solution whilst a drilling machine was sowing corn along the flight path. Samples of bees were captured on the dispenser, caged and held in the laboratory. Chemical analysis showed some hundred nanograms of insecticide per bee. Nevertheless, caged bees, previously contaminated in flight, died only if kept in conditions of high humidity. After the sowing, an increase in bee mortality in front of the hives was also observed. Spring bee losses, which corresponded with the sowing of corn-coated seed, seemed to be related to the casual encountering of drilling machine during foraging flight across the ploughed fields

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During the years 1992-93 a study on the dispersal of Trichogramma brassicae Bezd., an egg parasitoid of the European corn borer, Ostrinia nubilalis (Hbn.), was carried out in north-eastern Italy. In 1992 an Italian strain of trichogrammatid wasp and in 1993 a French strain were used. During August in two different plots of corn, about 4000 and 8 000 T. brassicae were released three times at one point per plot. Four checks of the 0. nubilalis egg masses on corn plants were made weekly in August; six distances from the point of release, ranging from 0.75 to 10.6 m, were considered. The rate of parasitization was higher in 1993 when T. brassicar at different developmental stages (larvae and pupae) were released. The percentage of 0. nubilalis egg masses parasitized by T . hrassicae decreased with the distance from the point of release. In both years, wind seemed to have an important effect on the dispersal of the parasitoid. The dispersal of T . brassicae was lower in the upwind sectors whereas in the downwind sectors increasing the distance from the point of release no significant decrease of the rates of parasitization was observed; the performances of the Italian and the French strains of trichogramma appeared to be the same. The results obtained in this experiment indicate that there should be a high number of release points per hectare to reduce the effects of both distance and wind, and parasitoids a t different developmental stages should be released to increase the rate of parasitization. The number of parasitoids released do not seem to effect the rate of parasitization.

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