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Does heterogeneity in crop canopy microclimates matter for pests? Evidence from aerial high-resolution thermography

Abstract:

A majority of agricultural pests are influenced by microclimatic conditions that affect their performance and occurrence. Thermal heterogeneity experienced by pests at fine spatial scales is potentially a key to understand pest dynamics, yet its study over entire fields at fine resolution has never been performed. We used aerial infrared thermography to yield high-resolution measurements of crop canopy temperatures in 38 potato fields in the Ecuadorian Andes. In each field, for 30 different plots, we characterized the spatiotemporal heterogeneity of crop canopy temperatures and simultaneously sampled populations of four common leaf-surface dwelling adult pests. We then evaluated the fine-scale thermal heterogeneity implications for pest occurrence and compared a variety of thermal spatial metrics with pest abundance and richness measured in field. We found that the range of temperatures available for pests in crop canopies was independent on scale: pests can access within few centimetres most of the thermal microenvironments recorded at the field level. Also, the availability of thermal microenvironments was dependent on solar radiations: with increasing radiation levels, pests have to travel less distance to reach a variety of thermal environments. At the plot level, we found that the four-studied pests were not clumped into their optimal thermal conditions but rather distributed evenly. Pests having a wide range of favourable microenvironments available within very short distances might be constrained by others factors (resources, enemies). However, we found that pest richness was significantly correlated to both thermal aggregation and diversity index, suggesting that more diverse and distinctly distributed thermal environments in crop fields shelter a higher diversity of pests. As environmental conservation and agronomical management increasingly depend on our ability to understand and pbkp_redict the responses of species to their environment, we recommend refining global pest distribution pbkp_redictions using fine-grained microclimatic models to infer accurate responses of organism to climate change. Indeed, fine-scale spatiotemporal heterogeneity of microclimates might provide organisms with more than enough suitable thermal habitats in their actual location to withstand global changes.