Abundance and sensitivity of beneficials in deciduous fruit as a decision tool for selectivity testing

Thirty-two selectivity tests on apple trees were evaluated in order to dete rmine the best timing for selectivity tests based on the predominance of va rious beneficial groups and their sensitivity to pesticides during the seas on. In the testing method used the whole insect populations of apple trees were measured. For the purpose of this evaluation the numbers of beneficial species were aggregated at the family/order level (Anthocoridae, Miridae, Nabidae, Coccinellidae, Hymenoptera and Araneae, respectively). Logarithmic ally transformed figures of the species counts in azinophos-methyl- and wat er-treated trees, plotted over the observation period, demonstrated that th e months of June to August are the most suitable ones for carrying out sele ctivity tests on fruit trees. The sensitivity of the various beneficial gro ups were obtained by comparing the logits of the mortality rates of azinpho s-methyl and water by weighted t-tests. The sensitivity did not vary greatl y over the testing season from June to October for all groups except Mirida e during the second half of the season. This can be explained by the predom inance of the less sensitive adults ready for hibernation.