Characterizing introduction, establishment and impact of an invasive insect pest in an urban landscape

The Asian citrus psyllid (ACP) is recognized as a serious threat to citrus worldwide. Understandably, the recent invasion of ACP in urban south California has alarmed the citrus agriculture industry. As an essential step towards managing the ongoing invasion, we analyzed ACP’s spatio-temporal distribution pattern in Southern California’s urban landscape to identify the ecological factors driving it. Analysis of ACP occurrences in relation to major roadways revealed that earliest occurrences of ACP are significantly closer to major roads than latter occurrences, suggesting that roads serve as important introduction pathways but that rapid natural spread of the psyllid is possible in certain environments. We then developed GAM-based habitat suitability models to identify the environmental and landscape contexts that contribute to ACP establishment and impact, with ACP presence and abundance as the respective response variables. Percent impervious surface was the best landscape predictor of both ACP presence and abundance, with a hump-shaped effect notable in both models. Among the bioclimatic variables, annual precipitation was the most contributing factor. Inclusion of prior ACP density within a 1 km radius as a lagged neighborhood effect improved both model fit and performance. The neighborhood effect was the best predictor of ACP presence, suggesting that small scale dispersal events contribute strongly to local establishment. For ACP abundance percent impervious surface and the neighborhood effect were equally important, suggesting impact is sensitive to urban environmental conditions. Overall, our study sheds light on the ecological factors that drives the invasion process of ACP at the landscape level.