After the determination of LD50’s on individual honey bees in laboratory conditions, it is necessary to enlarge the assessment of pesticide impacts using outdoor tests at the colony level. These higher-tiered semi-field tests are performed under insect-proof tunnels. A key characteristic of such tunnels, which are similar to those used for the production of some vegetable crops, is that they must be of sufficient size to permit “normal” bee activity (flight and foraging). Tunnels should be at least 120 m² - 150 m² (7-8 m x 20 m) and covered with a net that allows wind and rain into the tunnel to duplicate natural climatic conditions. In contrast, small cages of 9 m² (3 x 3 m) typically dedicated to plant selection cannot be considered for semi-field tests for various methodological reasons. The available space is too small and the numerous limited bees cannot fly around the queen-less one-frame hive.
Semi-field studies under insect-proof tunnels are largely based on the existing French CEB protocol n 230 (CEB, 2011). This kind of a test is intended to assess effects from a worst-case exposure scenario, where bees are confined to plants treated with a pesticide. Such studies under insect-proof tunnels are used to determine the following parameters:
- daily mortality,
- foraging activity and repellence effects,
- brood development,
- colony strength,
- behaviour of forager bees,
- residues on apiarist matrices (bees, honey, brood, wax…)