A semi-field approach to testing effects of fresh pesticide residues on bees in multiple-rate test

We describe a semi-field cage test specifically designed to test effects of delayed exposure to plant protection products. The trial involved the use of standardised mini-beehives. The principle of the trial was to prepare two groups of potted test plants per treatment. The first group of plants remained untreated, while the second group was treated at the desired rate and interval before exposure. Honeybee colonies, standardised with respect to age structure and total honeybee weight shortly before the start of the experiment, were enclosed individually in meshed cages of 20 m2. In these cages the bees were confined to the untreated plants for four days before the start of the exposure phase. During this period foraging activity and mortality were monitored daily. To enable a straightforward assessment of mortality, the colonies were manipulated such that no new adult honeybees would emerge during the trial period. In the evening before the initiation of exposure, the untreated plants were exchanged with treated plants. During the next four days daily monitoring of foraging activity and mortality was continued. The trial was concluded by inspecting the colony for brood development and presence of the queen and by determining weight loss of the colony. The relatively small size of the test units and the high degree of standardisation achieved with the set-up made the test highly reproducible and allowed for the simultaneous testing of various treatment groups (in our trial eight), including insecticide residues of different age classes, in a test design with various replicates per treatment (in our trial four). We show that the test can be used to evaluate the effects of plant protection products using several exposure scenarios, such as direct contact resulting from applications performed during bee flight, or simultaneous exposure to aged residues from applications performed at various predetermined intervals. We illustrate this using data from trials with the commercially available insecticides Reldan 22, Dursban 75 WG and PennCap