Postdispersal Weed Seed Predation by Crickets in a Rice Paddy Field after Irrigation Water Recedes

In this study, the relationship between the predation of weed seed by crickets and the distance from the edge of paddy fields after the irrigation water receded was investigated. In September 2011, the activity density of crickets and invertebrate seed predation were investigated twice in a paddy field at distances of 0, 5, 10, and 15 m from the field edge, and on a paddy levee. The activity density of all cricket species in the field was 2.8–4.6 individuals/trap/day (first trial) and 2.4–6.0 individuals/trap/ day (second trial), with no significant difference in activity density between the examined distances from the field edge. However, the cricket species differed in their spatial distribution. The activity density of Teleogryllus emma peaked at 5 m from the field edge, whereas that of Velarifictorus micado peaked 15 m from the edge. In contrast, the activity density of Loxoblemmus spp., including L. campestris, was higher on the paddy levee than in the field. The proportion of invertebrate seed predation on Echinochloa crus-galli var. crus-galli (23.9–40.9%/day) and Lolium multiflorum (81.0– 98.8%/day) did not differ significantly between the examined distances from the field edge. Camera recordings showed crickets to be the predominant invertebrate seed predators. These results suggest that crickets can help deplete weed seed banks over a large portion of paddy fields.