Abstract Context : Agricultural intensification has simplified agroecosystems, reduced biodiversity and weakened natural pest control. Effective biological control requires reliable, long‐term control of multiple herbivores. While studies investigated biological control in diversified cropping systems, there is little information as to what extent pest suppression is sustained throughout the growing season and whether it provides satisfactory control of several herbivores. Objectives : Here we assessed how increasing crop diversity and an ‘attract‐and‐reward’ (A&R) strategy influence the effectiveness and temporal stability of biological control. Methods : We compared predation, parasitism of eggs and caterpillars in a cabbage system with four levels of crop diversity: cabbage monoculture, cabbage‐oat strip cropping, strip cropping with six crops and an A&R system in which a strip cropping system was enhanced by inclusion of a parasitoid‐attractive cabbage cultivar and nectar‐providing buckwheat. Experiments were conducted at two organically‐managed farms in the Netherlands in 2023 and 2024. Additionally, a full‐factorial experiment was conducted in 2023 at one location to assess the effects of the A&R components. Temporal stability was quantified as the coefficient of variation and the proportion of sampling weeks in which each treatment exceeded the mean biological control level. Results : Across locations and years, strip cropping enhanced parasitism rates of Pieris brassicae and Plutella xylostella compared with monocultures. Pieris brassicae parasitism increased from 28% in monocultures to 58% in strip cropping systems, while P. xylostella parasitism rose from 10% to 25%–30%. Parasitism of Mamestra brassicae eggs by Trichogramma spp. reached up to 30% in the strip cropping system with six crops, compared with 1% in monocultures. A&R provided no improvement beyond standard strip cropping. Monocultures showed the highest coefficient of variation and exceeded the site‐year mean in only 13% of weeks, compared to more than 60% in strip crop systems. Synthesis and application : Our results highlight that strip cropping can enhance and stabilize biological control. Even simple two‐crop designs provide clear benefits over monocultures, while increasing crop diversity to six crops offers additional advantages. Because the temporal stability of biological control increases with crop diversity, designing strip cropping systems with more crops can help maintain consistent and resilient pest regulation throughout the growing season.
Bolletta et al. (Fri,) studied this question.