Trials in free flight

This method is used to evaluate the effect of direct exposure of a bee in flight to the powder emitted by the drill while sowing coated maize seed. Such a method is needed to test the hypothesis that bees, in repeated flights to flowering plants, can be expected to fly over plots being sown with coated maize seed and become lethally poisoned with powder acquired during the flight.

1) Bees from 4 hives can be conditioned to visit a feeder some 25 cm in diameter, containing a sucrose solution (50 w/v). The feeder can be progressively distanced from the hives up to a final distance of 100 m (see section Observing the bees, it is possible to count hundreds of bees flying, at an average height of 2 m, to and from the hives to the food source.

2) From the beginning of the sowing and at succeeding 15 minute intervals, bees can be caught in test tubes at the feeder and placed singly in small tulle cages (5 x 5 x 5 cm) and fed with a drop of honey placed on the mesh of the cage, and periodically renewed (every 6-12 h).

3) 24 samples can be captured at each time period, the first when the tractor starts and then every 15 minutes thereafter.

4) Each sample of 24 bees can be taken in cages to the laboratory and kept at a conditioned temperature of 22 ± 1.5°C (see section

5) For each time interval, 12 cages chosen at random are kept at laboratory humidity and the remaining 12 cages placed in a box at high humidity close to saturation (>95%). The raised relative humidity was obtained by placing the cages in a transparent plastic box sealed, but not hermetically, with a sheet of Plexiglas, and by placing a sheet of wetted absorbent paper at the base. The walls and the cover were sprayed with water and the cages were raised with a strip of polystyrene so that the bees could not get wet from any water that might remain on the base (Girolami et al., 2012a).