Studies on predatory arthropods in agricultural areas seldom include Diptera other than hoverflies, 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 (IPM). 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 IPM. 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.

中文翻译：

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苹果园捕食性节肢动物群落组成：果园管理、景观结构和采样方法

除了食蚜蝇外，对农业地区捕食性节肢动物的研究很少包括双翅目，部分原因是常见的采样方法对于捕获在受到干扰时容易飞走的物种的效果较差。为了在描述捕食者群落时研究这种偏差的影响，我们比较了传统的树枝节拍采样和抽吸采样，以描述瑞典苹果园的掠食性节肢动物群落，有机园和使用综合害虫管理 (IPM) 的果园。我们的结果表明，使用抽吸采样时，捕食性双翅目和寄生性膜翅目昆虫的比例显着增加（双翅目：32% 对 20%，膜翅目：25% 对 7%）。事实上，在使用抽吸采样时，掠食性双翅目是数量最多的掠食性群体，与蜘蛛是最丰富的群体的节拍采样相反。在被调查的苹果园中，一组在物种和个体中都特别丰富的掠食性苍蝇是 Hybotidae 科的舞蝇。尽管采样方法的偏差很明显，但令人鼓舞的是，方法的选择并没有影响关于捕食性节肢动物群落管理的结论。使用这两种方法，双翅目和鞘翅目捕食者在有机苹果园中的数量更多，而根据 IPM 管理的果园中的鸦类更丰富。包含景观变量进一步表明景观多样性和落叶林覆盖的影响，但捕食群体之间的反应符号不同。虽然鞘翅目和异翅目在被更复杂景观（高景观多样性和/或高落叶林覆盖率）包围的果园中更为丰富，但在这些果园中，蜘蛛、鸦科动物和双翅目昆虫的数量却相对较少。总而言之，我们的研究指出了苹果园中掠食性双翅目动物的潜在重要性，我们强烈建议未来对苹果和其他作物中的节肢动物掠食者进行研究，以积极包括掠食性双翅目。