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

Abstract Background and aims Crop cultivation practices and soil legacies are intrinsically linked and are hypothesized to influence plant direct and indirect defence against phytophagous insects. In this study, we tested how soils conditioned by push-pull (maize (Zea mays)- Desmodiumspp.- Brachiaria spp. intercrop) or maize monoculture (non-push-pull) affect maize (Zea mays) phytochemistry and subsequent resistance to fall armyworm (Spodoptera frugiperda Smith, Lepidoptera: Noctuidae). Methods Maize was grown in soils collected from push-pull and maize monoculture smallholder farmer fields. We compared maize growth, herbivore larval feeding, production of volatile and non-volatile 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 maize-Desmodium-Brachiariacompanion cropping conditioned soil had a better maize growth, higher and qualitatively different volatile and non-volatiles metabolites in plants in maize-Desmodium-Brachiaria companion cropping conditioned soil in comparison to plants grown in maize monoculture conditioned soil. Behavioural assays showed that S. frugiperda neonate fed more leaf tissue from maize plants planted in maize monoculture conditioned soil than those planted in maize-Desmodium-Brachiaria companion cropping conditioned soil. Parasitoid wasps were highly 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.