Soil Nutrient Enrichment Alters Trophic Linkages and Predator Efficiency in Cowpea-Aphid-Ladybird Systems

Abstract

Soil nutrient management can strongly influence interactions among plants, herbivores, and natural enemies. This study examined how organic and inorganic soil amendments affect tritrophic interactions among cowpea (Vigna unguiculata L. Walp.), the aphid Aphis craccivora Koch, and the predatory ladybird Cheilomenes sexmaculata Fabricius under semi-field conditions. Plants were grown in control, vermicompost, and NPK-treated soil to evaluate plant growth, aphid fitness, development of predator and its performance. Vermicompost significantly increased the number of leaflets per plant which reflected enhanced vegetative growth, while differences in leaflet shape were qualitative. It also enhanced the aphid fitness due to improved host quality. The total developmental period was significantly shortened and predation efficiency was highest at various prey densities in vermicompost treatment. Overall, vermicompost improved plant vigour and predator performance through improved prey quality, demonstrating a cascade effect across trophic levels. These results highlight vermicompost as a sustainable alternative to chemical fertilizers for promoting natural pest regulation and maintaining ecological balance in cowpea agroecosystems.