Windsor, F. M. | Search bioRxiv

bioRxiv2025

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.

ecology↗

bioRxiv2023

Sources of prey availability data alter interpretation of outputs from prey choice null networks

O_LINull models provide an invaluable baseline against which to test fundamental ecological hypotheses and highlight patterns in foraging choices that cannot be explained by neutral processes or sampling artefacts. In this way, null models can advance our understanding beyond simplistic dietary descriptions to identify drivers of interactions. This method, however, requires estimates of resource availability, which are generally imperfect representations of highly dynamic systems. Optimising method selection is crucial for study design, but the precise effects of different resource availability data on the efficacy of null models are poorly understood. C_LIO_LIUsing spider-prey networks as a model, we used prey abundance (suction sample) and activity density (sticky trap) data, and combinations of the two, to simulate null networks. We compared null diet composition, network properties (e.g., connectance and nestedness) and deviations of simulations from metabarcoding-based spider dietary data (to ascertain how different prey availability data alter ecological interpretation. C_LIO_LIDifferent sampling methods produced different null networks and inferred distinct prey selectivity. Null networks based on prey abundance and combined frequency-of-occurrence data more closely resembled the observed diet composition, and those based on prey abundance, activity density and proportionally combined data generated network properties most like dietary metabarcoding networks. C_LIO_LIWe show that survey method choice impacts all aspects of null network analyses, the precise effects varying between methods but ultimately altering ecological interpretation by increasing disparity in network properties or trophic niches between null and directly constructed networks. Merging datasets can generate more complete prey availability data but is not a panacea because it introduces different biases. The choice of method should reflect the research hypotheses and study system being investigated. Ultimately, survey methods should emulate the foraging mode of the focal predator as closely as possible, informed by the known ecology, natural history and behaviour of the predator. C_LI

ecology↗