Bliimel, S., Bakker, F. and Grove, A., 1993. Evaluation of different methods to assess the side-effects of pesticides on Phytoseiulus persimilis. Exp. Appl. Acarol., Two methods recommended by the International Organization for Biological and Integrated Control of Noxious Animals and Plants (IOBC) to test the side-effect of pesticide residues on Phytoseiutus persimilis in the laboratory were evaluated. The test on detached leaves resulted in an unacceptably high percentage of escaping individuals. This was not the case when the tests were performed in ventilated glass cages. To validate the results obtained in the laboratory additional experiments were performed on intact plants in the greenhouse. Results obtained on detached leaves underestimate effects found in the greenhouse, whereas effects measured in the glass cages are an overestimation. Besides the effect of residue on juvenile survival and adult reproduction, ovicidal effects and the effect of direct contact for adults and eggs were also taken into account in the evaluation. All tests were performed with endosulfan. It is concluded that the use of this compound at the recommended field concentration is not compatible with the use of P. persimilis.