Post-dispersal seed predation is one of the main causes of weed seed mortality and could contribute to biological weed control. In paddy fields, seed predators, including crickets, inhabit the levees during the summer crop-growing season. An important consideration for the biological control of weeds in the field interiors is the distance that predators penetrate into the paddy fields after the irrigation water recedes. In this study, we determined the penetration distance of crickets, which are expected to be efficient biological control agents for weeds, into the paddy fields.

The activity density of crickets and invertebrate seed predation within 0–15 m from the field edge were investigated using adhesive traps and seed cards (sandpaper glued with weed seeds) in a paddy field in Shizuoka, Japan. The activity density of crickets (2–6 individuals/trap/day) and seed predation of Echinochloa crus-galli var. crus-galli (24–41%/day) were constant as a function of distance from the field edge. Camera recordings showed that crickets were the predominant invertebrate seed predators. These results indicate that the crickets migrate at least 15 m from the levee into the field interior and can contribute to the seed bank depletion of paddy weeds.