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 determine the best timing for selectivity tests based on the predominance of various beneficial groups and their sensitivity to pesticides during the season. 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). Logarithmically transformed figures of the species counts in azinphos-methyl- and water-treated trees, plotted over the observation period, demonstrated that the months of June to August are the most suitable ones for carrying out selectivity tests on fruit trees. The sensitivity of the various beneficial groups were obtained by comparing the logits of the mortality rates of azinphos-methyl and water by weighted t -tests. The sensitivity did not vary greatly over the testing season from June to October for all groups except Miridae during the second half of the season. This can be explained by the predominance of the less sensitive adults ready for hibernation.