Arthropod predator nutrient content changes with wheat sowing period but is not driven by prey availability.

Abstract

Conservation biocontrol is crucial for crop pest management, but the impact of agricultural management practices on natural enemies of crop pests is poorly characterised. The timing of crop sowing could impact arthropod communities by altering basal resource availability and quality, manifesting in altered nutrient availability for herbivorous arthropods and cascading impacts on natural enemy fitness and function. This study investigates how the timing of crop sowing impacts arthropod predator nutrition and whether associated differences relate to changes in prey availability. Arthropod predators and their prey were collected from adjacent plots of winter- and spring-sown wheat. The biochemical macronutrient (carbohydrate, lipid and protein) content of predators was determined by colourimetric assays and compared between winter- and spring-sown crops using multivariate models. Predator nutrient contents were compared to prey availability inferred using null network models based on both recent and current prey abundances. The nutrient contents of arthropod predators differed significantly between winter- and spring-sown wheat, driven by differences in carbohydrate content, and prey abundances similarly differed, but neither recent nor current prey availability explained differences in predator nutrition. These findings may indicate that prey quality, rather than identity, changes with the developmental stages of crops sown at different times. The different nutritional states of predators in crops sown at different times may have important implications for the spillover of natural enemies of crop pests between crops.