Analysis of the spread of Rhynchophorus ferrugineus in an urban area, using GIS techniques: a study case in Central Italy

The spread of the red palm weevil is now a very severe problem on a global scale. In this paper, we investigate its spread during the 2007–2013 period in a coastal urban area characterized by a high density of palm trees, and discuss the application of a new approach to data collection and processing. While most works on the spread of the red palm weevil are based upon geo-referenced traps, we focused on the health of each palm, considering the surrounding territorial context. To this end, we used historical aerial photos, freely available remote sensing images and field surveys, integrated in a GIS environment to analyze the extent and mode of pest spread over time. Our results show that the exponential increase of new cases for each new year is regulated by this spatial spread model: at the early stage of infestation the red weevil tends to occupy as much space as possible, within the limitations of the distance it can fly; in the following stage, its infestation density increases in recently colonized areas. We discuss current local management of palm trees and the pests, and propose strategies that take into account both the ecology of the red weevil and the territorial context. Finally, we encourage the provision of more resources for early detection and prevention measures, as well as replacement of the dead Phoenix canariensis palms with a greater variety of species, as a varied composition would be less prone to pest-caused depopulation.