Sampling methods in orchard trials: A comparison between beating and inventory sampling

Two methods to assess leaf dwelling arthropods in the tree canopy of orchards, which are used in studies to investigate effects of pesticides on non-target arthropods, were compared: beating sampling and inventory sampling. Both methods were applied at the same time in the same apple orchard in Southern Germany. Each inventory sample comprised the catches of one tree, each beating sample the catches of 20 branches. In order to investigate, if both methods are able to detect changes in arthropod abundances in a comparable way, samples were taken before and after a treatment with a toxic compound. Additionally, samples were taken in a water treated control area. Besides the arthropods collected, supplementary information concerning time, manpower and necessary plot sizes needed for the different methods was assessed. Excluding spot wise occurring arthropods the variability between replicates was comparable for both sampling methods, with few exceptions. The mean number of arthropods in the inventory samples was 3 times higher than in the beating samples in the pre-treatment sampling, and 2 times higher in the post-treatment samples. Reductions in arthropod abundances after treatment with the toxic compound, were revealed with both methods in a similar order of magnitude for Opiliones (> 80 %), Dermaptera (F. auriculuria) (>90%), and Heteroptera (>76%). With regard to Araneae, inventory samples revealed higher reductions than the beating samples. Highly moblile arthropods, like e.g. Hymenoptera and Diptera, were difficult to assess with the beating sampling method. For these groups inventory sampling achieved higher portions in sample composition as well as more information concerning changes in abundance. Beating sampling is considered an adequate method for studies, which demand a continuous and/or flexible sampling schedule in trials where arthropods are relatively abundant at the test site. Compared to inventory sampling beating is a low input method concerning time and manpower. Highly mobile arthropods should be assessed with additional sampling techniques. Inventory sampling in contrast is of preference for test sites with lower abundance of arthropods and when a comprehensive assessment of the species diversity is demanded. Whether with inventory sampling reliable information concerning highly mobile/aerial arthropods can be obtained, needs further investigation