Insect movement and spatial dynamics determine trap crop effectiveness

Danish A. Ahmed, Noor Tahat, Isadora Fluck Essig, Matthew Holden, Joseph Bailey, Francisco Rubén Badenes-Pérez, Emma J. Hudgins, Philip E. Hulme, Fabrice Vinatier

Trap cropping diverts pest pressure away from cash crops, yet its effectiveness depends on pest movement behaviour and the retention or removal processes that occur after insects reach trap plants. We develop a one-dimensional movement-based modelling framework in which pest trajectories follow a biased correlated random walk within a spatially structured field containing trap-crop interception zones of varying size. The model represents attraction towards trap crops, directional persistence in pest movement, and post-encounter retention or removal within the trap crop zone. We analyse how movement behaviour, retention strength, and the allocation of land between cash and trap crops influence interception dynamics and pest removal under ecologically realistic conditions. We find that trap crop effectiveness depends on the interaction between attraction and retention. Attraction alone does not guarantee pest suppression because insects may traverse the trap crop with residence times too short for removal processes to reduce pest abundance. In contrast, interception and retention mechanisms lead to suppression through distinct processes: strong entry interception leads to rapid pest removal, whereas behavioural arrestment increases trap crop occupancy and reduces emigration from the field. When retention is weak, insects escape after crossing the trap crop strip, limiting trap cropping effectiveness. The model reveals trade-offs among trap crop size, pest suppression, and the allocation of land between trap and cash crops. By linking pest movement dynamics with trap crop spatial allocation, this framework provides a mechanistic basis for predicting trap cropping performance and highlights the importance of retention in improving trap-based pest management strategies.