Recently, my first paper was published in the Journal of Applied ecology, named ‘Modelling agricultural landscape complementation for natural pest control’. As the name might already suggest we used a mathematical model to study the impact of the agricultural landscape on natural pest control in arable crops. Here, I wanted to give a short overview of our findings and what they could mean for landscape design in arable farming systems.
Enhancing Natural Pest Control: The Role of Habitat Diversity
In today’s agriculture, balancing effective pest control with ecological sustainability is a pressing concern. A key solution lies in understanding how the composition of landscapes affects the natural enemies that help manage pest populations. Our recent study has taken an innovative approach to explore this dynamic through landscape-based population-dynamical modelling, providing new insights into optimizing natural pest control.
Understanding Landscape Complementation
Natural enemies of agricultural pests, such as predatory hoverflies, require various habitats to meet their needs throughout their life cycles, from winter and prey habitat to sources of nectar and pollen. This concept is known as “landscape complementation,” which emphasizes that the best outcomes for populations and ecosystem services occur when different types of habitats complement each other by providing a range of resources and conditions in close proximity. However, modern agricultural practices have often led to homogenized landscapes with large monocrop fields and fewer semi-natural areas, challenging biodiversity and ecosystem services like pest control.
Modelling Natural Pest Control Dynamics
To address these challenges, we developed a model focusing on the interactions between predatory hoverflies (Diptera: Syrphinae) and aphid prey (Homoptera: Aphididae) in multi-habitat landscapes typical of North-Western Europe. The model integrates predator-prey interactions and seasonal resource dynamics in different habitats, offering a comprehensive understanding of how landscape composition affects natural pest control.
Key Findings from the Model
• Habitat Complementation is Essential: The model shows that a mix of woody habitats, varied crops (early and late-season), and flower margins is most effective in reducing pest densities. In practice, various habitat combinations, including crops and (semi-)natural habitats, can enhance natural pest control as long as these habitats are complementary by providing (the same) resources in different periods of the year and vice versa. Eliminating any habitat type cannot be compensated by merely increasing the others, underscoring the importance of landscape complementation.
• Biennial Cycles of Pest and Predator Abundance: The model reveals biennial cycles in predator and pest populations, driven by predator-prey dynamics. High pest densities early in the year boost predator populations, leading to low pest and predator numbers the next year. Such cycles have also been observed in real-world settings, such as in aphid populations in various crops and trees. Interestingly, these cycles change when removing certain habitats from the landscape. Depending on which habitat is removed, the densities between years can fluctuate more, the cycles disappear combined with only very high pest densities, or the cycles become more complex, taking more than 2 years to repeat themselves.
• Effectiveness of Flower Margins and Crop Diversity: Flower strips with accessible floral resources significantly reduce pest densities, but their effectiveness depends on surrounding landscape composition and resource quality. Similarly, crop diversity —at field or landscape level— was shown to have a positive impact on natural pest control.
• Woody Habitats as Year-Round Refuges: Woody habitats play a vital role by offering resources when other habitats do not, supporting predator persistence year-round. This aligns with empirical studies that highlight the importance of woody habitats for maintaining natural pest control.
Practical Implications for Agricultural Landscapes
The insights from this model have significant practical implications for sustainable agriculture. Here are a few takeaways for enhancing natural pest control:
• Designing Effective Landscapes: An optimal agricultural landscape for natural pest control should include a diverse combination of habitats that provide complementary resources throughout the year. This may involve a mix of woody areas, varied crops, and flower margins to ensure continuous support for natural enemies like hoverflies.
• Reconsidering Field Margin Strips: Field margins must provide appropriate floral resources tailored to natural enemies. Not all flower strips are equally effective, and their impact is influenced by the surrounding landscape, which could explain inconsistent results in empirical studies.
• Overcoming Limitations of Empirical Studies: Many studies rely on snap-shot surveys during the main crop-growing season, lacking variations in resource availability and predator-prey dynamics. This can lead to misleading conclusions about the effects of landscape elements. Our study addresses these limitations by modelling interactions across all seasons, revealing resource discontinuities that act as bottlenecks for natural enemies and providing a comprehensive understanding of landscape-level processes.
• Improving Study Design and Interpretation: The model shows that using predator abundance as a proxy for pest control can be misleading. Effective predators reduce their own food resources, leading to lower densities. Future studies should consider resource levels and predator-prey dynamics over different seasons rather than relying solely on predator abundance at specific times.
Moving Forward: Future Directions in Natural Pest Control
While the current model offers valuable insights, it operates under a spatially implicit framework—meaning it does not consider the exact spatial arrangement of habitats, but assumes that they are within reach of hoverfly movement. Future studies could benefit from incorporating spatially explicit elements to provide more nuanced, location-specific recommendations.
Moreover, expanding the model to include multiple predator species and considering their interspecific interactions could further refine our understanding of natural pest control dynamics. This would help in making more robust predictions and identifying the most effective landscape configurations.
Conclusion
As agriculture evolves, integrating ecological principles like landscape complementation into land management will be crucial for sustainable pest control. This study’s modelling approach provides valuable insights into how different habitats support natural enemies and offers actionable strategies for enhancing biodiversity and ecosystem services in agricultural landscapes. By designing landscapes that support natural pest control, we can reduce reliance on chemical pesticides, promote biodiversity, and move towards sustainable food production systems.
Mansier, L., & van Rijn, P. C. J. (2024). Modelling agricultural landscape complementation for natural pest control. Journal of Applied Ecology, 00, 1–16. https://doi.org/10.1111/1365-2664.14790