Arthropod predator nutrient content changes with crop sowing period with implications for biocontrol

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 and cascading impacts to natural enemy fitness and function. This study aims to understand these potential modifiers of conservation biocontrol, by investigating 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 colorimetric assays and compared between winter-and spring-sown crops using multivariate models. Predator nutrient contents were compared to predator-prey interactions inferred using null network models based on both recent and current prey availability. The nutrient contents of arthropod predators differed significantly between winter- and spring-sown wheat, and the prey available to predators 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. This has important implications for the spillover of natural enemies of crop pests between crops sown at different times. This is especially true following harvest of winter-sown crops, which may disrupt biocontrol by altering the nutrients available to and sought by natural enemies of crop pests.