Ladybeetle dispersal from adjacent wheat or maize fields promotes aphid biocontrol in cotton

Cotton is a major cash crop in Xinjiang, which heavily relies on the use of pesticides to control pests. Enhancing biological control through natural enemies offers potential to reduce pesticide use, but little is known about the seasonal sink-source dynamics of natural enemies. We measured the movement of adult ladybeetles into cotton fields from adjacent wheat, maize and cotton fields using transparent sticky cards in 2022 and 2023. We also monitored aphid and ladybeetle densities and assessed predation activity using cotton bollworm egg cards in cotton fields bordered by cotton, wheat, or maize fields. More ladybeetles moved from wheat (37%) and maize (23%) into cotton than the reverse, indicating a net spillover from cereal crops into cotton. Aphid densities in cotton fields next to wheat were 42% lower than next to cotton, while for maize this relationship was not significant. However, peak aphid densities in cotton fields adjacent to maize were lower than in cotton fields next to other cotton fields. Predation activity in cotton next to wheat and maize was 48 and 27% higher than in cotton-cotton fields, respectively. Wheat supported the reproduction of ladybeetles, as evidenced by high densities of ladybeetle larvae, while this was less the case for maize. Adjacent wheat and, to a less extent, maize crops enabled an earlier ladybeetle migration into cotton, resulting in higher early-season ladybeetle densities, enhanced aphid control, and slower population growth of cotton aphids. Integrating wheat and maize into cotton systems can therefore strengthen natural pest regulation through enhanced biocontrol. • More ladybeetles moved from wheat and maize fields to cotton than vice versa . • An adjacent wheat or maize field lowered cotton aphid abundance in cotton. • The adjacent crop effect on ladybeetle abundance extended at least 50 m into cotton. • Predation activity in cotton was enhanced up to 25 m from the interface.