果樹園における地表徘徊性天敵類を対象としたピットフォールトラップ調査法の検討：トラップ捕獲結果に対する容器サイズの影響

概要

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Pitfall traps are commonly used in the assessment of ground dwelling organisms. Such traps have been proposed as a main tool for the investigation of agro-ecosystem biological diversity in Japan. We evaluated the effects of pitfall trap cup sizes on catches of epigeal invertebrate predators in an orchard. Traps with seven different cup sizes (5.3–13.0 cm diameter) were positioned in the orchard in early summer and in autumn. For each taxon or species of invertebrate, we performed regression analyses of the mean catch per day for each trap size. There was no effect of trap size on the number of catches per day for carabid beetles (Carabidae spp.), striped earwigs (Labidura riparia), or wolf spiders (Lycosidae spp.). On the other hand, the number of dome spiders (Lyniphiidae spp.) captured in summer increased with trap size. These differences seemed to reflect differences in population densities. We concluded that when pitfall traps are used for the short-term assessment of ground dwelling organisms in the orchard environment, the results will not be significantly affected by trap cup sizes, at least within the easily available size range of 6.5–10.0 cm in diameter.