Flowering zinnia as companion plant increases predatory arthropod abundance and improves yard-long bean yield

Companion plants can play a role in agroecosystems by supporting predatory arthropods, thus enhancing their biological control services. However, the effects on natural pest control and crop productivity associated with the blooming periods of companion plants remain unclear. We examined how the presence of seedling, vegetative, and flowering stages of zinnia (Zinnia x hybrida) as a companion plant affected predatory arthropod populations and their biological control of cowpea aphids (Aphis craccivora), and crop productivity in yard-long bean (Vigna unguiculata subsp. sesquipedalis L.) intercropping system compared to yard-long bean monoculture (control) over three cropping seasons in 2019-2020. We found a significant increase in the abundance of coccinellids (Coleoptera: Coccinellidae) and syrphids (Diptera: Syrphidae), and in crop yields when flowering zinnia plants were provided at the start of the crop season, with varying degrees among seasons. However, zinnia had no observed impact on cowpea aphid reduction. These findings demonstrate that the early arrival of predatory arthropods in vegetable crops could be enhanced by initially providing floral resources from zinnia at the beginning of the crop season, contributing to yield improvement. Zinnia could be an effective companion plant, offering alternative resources for predatory arthropod colonization and promoting their biological control service of certain pests in legume crops.