DOI: 10.5061/dryad.p8cz8w9n2
title: Predatory arthropod community composition in apple orchards: Orchard management, landscape structure and sampling method

description: Studies on predatory arthropods in agricultural areas seldom include
 Diptera other than hover flies, partly because common sampling methods are
 less effective for capturing species that easily fly off when disturbed.
 To study the effect from this bias when describing the predator community,
 we compared traditional beat sampling of branches and suction sampling for
 describing the community of predatory arthropods in Swedish apple
 orchards, both organic orchards and orchards using integrated pest
 management. Our results indicate that the proportion of both predatory
 dipterans and parasitic hymenopterans increase dramatically when using
 suction sampling (Diptera: 32% vs 20%, Hymenoptera: 25% vs 7%). In fact,
 predatory dipterans were the most abundant predatory group when using
 suction sampling, in contrast to beat sampling where spiders were the most
 abundant group. One group of predatory flies that was particularly rich in
 both species and individuals in the surveyed apple orchards was dance
 flies in the family Hybotidae. Even though the bias of sampling method was
 evident, it was encouraging that the method choice did not affect the
 conclusions concerning management on predatory arthropod communities. With
 both methods, dipteran and coleopteran predators were more abundant in
 organic apple orchards whereas opilionids were more abundant in orchards
 managed according to integrated pest management. The inclusion of
 landscape variables further indicated effects of landscape diversity and
 of deciduous forest cover, but the response varied in sign between
 predatory groups. Whereas both Coleoptera and Heteroptera were more
 abundant in orchards surrounded by more complex landscapes (high landscape
 diversity and/or high deciduous forest cover), spiders, opilionids and
 dipterans were rather less abundant in these orchards. To conclude, our
 study points to the potential importance of predatory dipterans in apple
 orchards, and we highly recommend future studies of arthropod predators in
 apple and other crops to actively include predatory Diptera.
description: The data were collected in 28 apple orchards in S Sweden (14
 organic and 14 IPM), using either beating sampling (in 2015) or suction
 sampling (in 2016). Landscape data were retrieved from the IACS data base
 within 1 km from the sampling point. Selected habitats (excluding roads
 and other human constructions) were then calculated as the proportion of
 the total area. Samples were only sorted to predatory group, except for
 Diptera that were identified to species.
description: 'Data file Predatory Arthropods.xls' contains all
 environmental data, abundance data of broad predatory groups (Coleoptera,
 Aranae, Heteroptera, Hymenoptera, Neuroptera, Opiliones, Diptera,
 Dermaptera) and dipteran subgroups (Hybotidae, Dolichopodidae), and number
 of captured species of selected dipteran groups (Empididae, Hybotidae and
 Dolichopodidae). Diptera diversity is calculated as the pooled value of
 2015 and 2016, using the combination of samling methods. Missing values
 indicated with NA. Environmental data describe
 collection year (2015 = beat sampling, 2016 = suction sampling), orchard
 type (organic, IPM), site identity, 8 variables describing proportional
 cover of habitats within a 1 km radius (cereals, flowering crops,
 perennial crops, wetlands, conifers, broadleaved trees, seminatural
 grassland and gardens), a measure of landscape diversity (Shannon
 diversity of recorded landscape categories) and %flower cover within
 orchards.  Abundance data describe number of captured
 individuals per orchard. 2015: Beat sampling was conducted on 24 trees per
 orchard and one branch per tree. The trees were located along a 40 m
 linear transect from field edge towards field interior. The size of
 sampled branches was selected to be similar to the beating tray. The tray
 consisted on a 65 × 50 cm wooden frame with a handle supporting a
 quadrangular funnel-shaped cloth (50 cm high) sloping down towards the
 center to a cup containing 70 % ethanol. 2016: Suction sampling was
 conducted using the InsectaZooka suction sampling device (Bioquip
 Products, Rancho Dominguez, CA, USA) for 10x2 minutes per orchard. During
 each 2 minute sampling, we collected insects in a short stocking placed at
 the inlet (diameter 6 cm) of the suction sampling device and each sample
 contained arthropods from branches on 2-3 neighboring apple trees
 depending on apple tree size. Thus, the total number of sampled trees was
 similar between beat and suction sampling. At the end of each 2 minute
 sampling, the stocking was removed, sealed and placed in a cool box for
 transportation. 'Dipteran community data.xls'
 contains all data on dipteran abundance at the species level.