Local and landscape effects on the occurrence and abundance of the Eucalyptus weevil Gonipterus platensis (Coleoptera: Curculionidae)

Abstract The weevil Gonipterus platensis is among the most important eucalypt (Eucalyptus spp.) pest species worldwide. In Portugal, weevil-induced damage has great economic significance and efforts are being taken to find adequate alternatives to the biological control of this defoliator by its parasitoid Anaphes nitens, which is ineffective at altitudes above 400 m. With the aim of improving current knowledge on the ecology of G. platensis, we evaluated its interactions with local and landscape factors through the application of generalized linear mixed models for (1) the probability of weevil occurrence in sampling points, and (2) the relative abundance of each of its two annual generations on eucalypt trees. Our models confirmed the significant positive effect of elevation, here found to come off just above 360 m a.s.l., on both the occurrence and the abundance of G. platensis. Moreover, our results denoted that stand-level variables can likewise affect this pest. Points located more than 400 m inside the stands and, to a lesser extent, those comprising smaller (yet mature) eucalypt trees and where trees of other species were absent, showed an increased probability of G. platensis occurrence. Concordantly, significantly higher abundances of both weevil generations were observed on 3–8 years-old eucalypt trees. In addition, there was a negative effect of coppiced stands on G. platensis abundance which was only significant for the first annual generation and probably was related with weevil’s recent colonization of stands ravaged by wildfires two years before our field surveys. Weevil populations were not influenced by the density of stand canopy, neither by understory structure and composition, nor by bare soil cover, hence it is not expected that thinning, shrub removal and soil scarification practices can affect G. platensis attacks in eucalypt stands. Overall, our study provides key knowledge on the ecology of G. platensis and its response to local and landscape features, paving the way for enhanced management of eucalypt plantations.