4.2.2. Tunnel description
1) The tunnels (Fig. 7) are placed side by side and separated from each other by a minimum distance of 2 m. All tunnels have the same orientation for common disposal. The tunnel nets are stretched out and embedded alongside the tunnel, thus creating a closed environment limiting foragers' flights. This space appears nevertheless sufficient after adaptation. Rain and wind, though weakened, are able to pass through the net. Temperature is sometimes a little higher in the tunnel than outside, but generally, there is small difference between the two environments (± 1°C).
2) Attractive plants are grown under tunnels in order to trigger foraging activity. These include Phacelia tanacetifolia, oilseed rape (Brassica napus) or mustard (Sinapis alba). When the trial is dedicated to behaviour assessment, sunflowers are convenient for their large flowers where forager bees can be easily observed. In the special case of the use of a pesticide against aphids on cereals, the crop should be winter wheat where bees are attracted by the daily spray of a sugar solution simulating the aphids’ honeydew.
3) Inside each tunnel, 4 plots of the same size (2m x 8m) are delimited and separated by areas covered with a film of synthetic material, where vegetation has been removed (Lane 1 to Lane 6, see Fig. 8). The dimensions of these plastic-covered areas are adapted to the tunnel dimensions but the peripheral paths (Lane 1, Lane 3, Lane 4 and Lane 6) are at least 1m wide. The 4 plots (T1 to T4) receive foliar applications. The same relative plot position is adopted in all tunnels.
4) The hives (see section 4.2.5.) are placed in the central parts of the tunnels (Lane 2), as shown in Fig. 8. The entrance of the hive is directed towards the water supply on the central path. After placing the colonies in the tunnels, a water source is provided on the central path. The water source is removed during the foliar application.
5) After a few days of confinement, foraging bees'
activity is adapted to the considered area.
7. Example of a tunnel used for semi-field toxicity tests.
Fig. 8. Tunnel design of 4 plots to be treated and dedicated covered plastic lanes to collect dead bees.