Push-pull cropping system soil legacy alter maize metabolism and fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) resistance through tritrophic interactions

Background and aims Crop cultivation practices and soil legacies are intrinsically linked and are hypothesized to influence direct and indirect plant defences against phytophagous insects. In this study, we tested how soils conditioned by push-pull (maize (Zea mays)- Desmodium spp.- Brachiaria spp. intercrop) or maize monoculture (non-push-pull) affect maize phytochemistry and subsequent resistance to fall armyworm (Spodoptera frugiperda Smith, Lepidoptera: Noctuidae). We hypothesised that conditioning soil with push-pull positively impacted maize growth, metabolism, and subsequent direct and indirect resistance to an invasive herbivore pest.Methods Maize was grown in soils collected from push-pull and maize monoculture fields. We compared maize growth, herbivore larval feeding, production of defense secondary metabolites on maize grown in soils conditioned by push-pull and non-push-pull cropping. As a proxy for indirect defence effects, we also measured behavioural responses of egg-larval parasitoid Chelonus bifoveolatus Szpligeti (Hymenoptera: Braconidae) to maize volatiles from plants planted in soils conditioned by each cropping system.Results Maize plants grown in soil conditioned by push-pull had a higher biomass accumulation and plant height. Higher quantities and more diverse volatile and non-volatiles metabolites were observed in maize grown in push-pull soil in comparison to those grown in maize monoculture soil. Behavioural assays showed that S. frugiperda neonate fed more on leaf tissue from maize plants planted in soil conditioned by maize monoculture than those planted in push-pull conditioned soil. Parasitoid wasps were more attracted to volatiles from maize planted in push-pull conditioned soils than those planted in non-push-pull soils.Conclusion Our results indicate that conditioning soil with polyculture push-pull enhances maize growth, alters phytochemistry and subsequent direct and indirect resistance to S. frugiperda.