Trials in mobile cages

1) In trial set up to evaluate the presence, consistency, extent and duration of the toxic cloud surrounding pneumatic seed drills during the maize sowing season, and using seed coated with insecticide, the powdering was evaluated by means of an aluminium bar 4 m long, to which cages, each containing a single bee, were attached every 0.3 m (12 in total) (Figs. 2 and 6).

2) The bar was supported at each end by a vertical pole of 2.5 m. The bar was passed by two people at a fast walking pace (6-8 km/h) by the side of the drilling machine, at a variable height according to how the exhaust air was emitted from the machine, taking into account that bees fly predominantly at 1-3 m over ploughed land (unpublished data). The cages may be numbered considering the progressive distances from the drill.

3) The people with the bar followed and passed the tractor on the right hand side (in the first 30 m of the plot) (Fig. 6). The tractor then reduced speed and waited while the people with the bar made a U-turn and again passed the machine, once more at working speed, on the left hand side. In this way, the bees were twice exposed to the cloud in a similar way to foragers in free flight making a round trip over the sowing area.

4) To evaluate the mortality, once the bees had been exposed to the insecticide dust in a cage in the field, they were transferred (inside the same cage) to a room at a controlled temperature (22 ± 1.5°C) and in conditions of high humidity (Girolami et al., 2012b but see section

Fig. 6. Exposure of bees using the mobile cage method.

1298JDE revised Fig6