4.2.6. Treatment methodology
1) After hive settlement under the tunnels, the bees will forage on crop plots and strength parameters can be assessed (Delaplane et al., 2013b) for 2 to 5 days until decreasing mortalities are homogeneous within modalities.
2) The number of semi-field tunnels is defined by the objectives of the study and includes at least 4 tunnels:
- two tunnels for the pesticide in question
- control tunnel (negative reference)
- reference tunnel (positive reference)
3) The tested pesticide has to be applied in two modalities. The first duplicates GAP (i.e. applied according to label) and the second includes “the worst case of exposure”. Therefore the first pesticide application occurs during flowering but when bees are not present in order to avoid contact with forager bees (after bee flight generally at night). The second tunnel receives a pesticide application while the bees are foraging on the test crop. To ensure adequate bee exposure for the second modality, there should be at least 5 forager bees/m² crop at the time of the foliar application
4) In the negative reference tunnel, the test crop plots are treated with water in order to determine any physical effect of the spray.
5) The reference tunnel (positive reference) exists to demonstrate bee sensitivity to a pesticide and to validate the trial. Dimethoate (400 g AI/ha) should serve as the toxic standard in the reference tunnel. It provides a high peak in mortality after application. It is, therefore, possible to add replicates of these four initial tunnels in a single study, or to conduct the study again in other conditions.
6) When the semi-field test is used to determine the behaviour of forager bees exposed to no foliar pesticide application (i.e. coated seeds or soil treatment), the test design has no toxic reference (positive reference, one does not exist) and only two modalities are needed (treated and negative reference).