Floral availability outweighs aphid presence in supporting coccinellid abundance across life stages and promotes aphid predation

Abstract

The nature of the prevalent interactions within communities influences biodiversity–ecosystem service relationships, which could be strengthened as habitat and resource diversity promote species coexistence. When species share similar resources, their coexistence can enhance complementarity among predatory species in providing biological control in agroecosystems, depending on how different life stages of predatory insects use crop and non-crop habitats. To test these predictions, we assessed how different aphidophagous coccinellid life stages use crop and non-crop habitats and their consequences for aphid predation in organic tropical agroecosystems. We sampled all coccinellid life stages (abundance, species and diversity) and estimated aphid predation through a predator exclusion experiment in Brassica organic farms in Brazil. The use of both crop and non-crop plants (notably Asteraceae) by coccinellids increased their overall abundance within farms. We found no significant differences in the numbers of coccinellid eggs, larvae, pupae, and adults between crop and non-crop plants. However, our findings suggest that crops and non-crop habitats may play distinct roles for each life stage: crops might primarily provide prey, while non-crop plants could offer shelter and supplementary food. Indeed, coccinellid abundance was higher when flowers were present in non-crop plants, regardless of aphid presence. We found a positive relationship between coccinellid abundance and aphid predation only when coccinellid diversity was high. When diversity was low, the high dominance of a single species limited aphid predation. Therefore, species complementarity resulting from habitat partitioning across coccinellids’ life stages may emerge as a central mechanism influencing the positive biodiversity-ecosystem service relationships in tropical agroecosystems.