Biocontrol in insecticide sprayed crops does not benefit from semi-natural habitats and recovers slowly after spraying.
To enhance biological pest control in crop fields, it is recommended to increase semi-natural area on farm and decrease insecticide spraying. While the benefits of semi-natural area for biocontrol in unsprayed fields are often demonstrated, it remains largely unknown if there are any benefits in real-world, commonly sprayed crops. Here, we explored the combined effects of semi-natural field margins and insecticide spraying on pest (cotton bollworm) egg predation in 53 Australian cotton fields and semi-natural field margins across 2 years. We used predation experiments close to field edges to exclude functional groups of predators depending on their spatio-temporal activity (diurnal vs. nocturnal and ground vs. canopy dwelling) and digital cameras to record natural enemy taxa responsible for predation. Ground predation was substantially higher than canopy predation and its magnitude in unsprayed crops with semi-natural margins was similar to that within semi-natural areas. In contrast, semi-natural field margins did not benefit biocontrol in sprayed crop fields and did not influence recovery rate of biocontrol after spraying. Within ground-dwelling predators, one dominant taxon contributed the most to biocontrol at a particular time and place. However, the dominant predator-prey interactions changed between day and night and fields with and without margins, thus indicating increased importance of additional predator taxa with increasing spatio-temporal scales. Synthesis and applications. Our results show that semi-natural margins benefit pest control only in unsprayed fields. Spraying at different time (e.g. during night) would not reduce the negative effects of insecticides because it would affect complementary group of nocturnal natural enemies that exert equally high biocontrol as diurnal ground-dwelling predators. We highlight the need for management recommendations to simultaneously consider pros and cons of within-field spraying and surrounding semi-natural habitats to maximize their benefits in high-input conventional production systems.