A multi-scale approach to study palm-weevils in a tropical agroecosystem

Abstract

Context: The recent phytosanitary crisis caused by the stem borer weevils Dynamis borassi and Rhynchophorus palmarum in peach palms (Bactris gasipaes) seriously affects the economy of rural families in Colombia. To understand the possible ecological mechanisms favoring the pest, the weevil-palm system needs to be studied from a multi-scale perspective. Objectives: We evaluated the combined effects of agricultural management, landscape, topography, soil, and climate variables on infestation levels of peach palm caused by the weevils D. borassi and R. palmarum in the Colombian southwest to understand underlying ecological drivers of the current phytosanitary crisis. Methods: The palm infestation levels (response variable) and local agronomic practices were recorded in 32 sites across Colombia's Pacific, Andes, and Amazon natural regions. For each peach palm crop, landscape variables were estimated from classified Sentinel-2 images, soil variables were extracted from the Soil Grids 250 m database, and climate variables were extracted from the CHIRPS and CHIRTS databases. Explanatory variables were analyzed using Generalized Linear Models and Partial Least Squares-Generalized Linear Models. Results: Landscape variables, specifically the number and shape of non-forest patches, had a greater influence on peach palm infestation levels than other environmental variables, possibly related to the decrease in the density of Oenocarpus batatua, the natural palm host for D. borassi, leading it to switch to the peach palm. Conclusions: A multi-scale approach of the weevil-palm interaction enabled us to identify an ecological mechanism that has not been proposed before. Our recommendation for families depending on peach palm is to design palm management with a landscape perspective that considers the conservation of alternative hosts for the weevils in agroforestal plots.