Drivers and spread of non-native pests in forests: The case of Gonipterus platensis in Spanish Eucalyptus plantations

Plantations of Eucalyptus species have been widely used in Spain to meet the high demand for wood given their rapid growth and high wood production capacity. Defoliation induced by the invasive eucalypt weevil (Gonip-terus platensis (Marelli)), however, has been causing significant economic damage to Spanish Eucalyptus spp. plantations since the 1990s. G. platensis is native to Tasmania, Australia, where populations are controlled by natural enemies including the egg parasitoid Anaphes nitens Girault. In this study, spatio-temporal Universal Kriging was applied to examine the dynamics of defoliation damage caused by G. platensis in Spanish Eucalyptus spp. plantations and to identify the main factors associated with the presence and spread of the pest. The data set combines the Spanish national plots belonging to the network of the European transnational survey of forest condition in Europe (ICP Forest Level I, 16 x 16 km grid) along with regional plots, measured using similar field protocols, in which Eucalyptus spp. are present. A total of 264 Eucalyptus plots were included in the study, G. platensis being present in 167 of these plots at some time during the observed period (2005-2020). Our results show that defoliation damage > 0% and defoliation damage > 5% caused by G. platensis increased over the period 2005-2010 and then decreased between 2010 and 2020. Defoliation damage > 15% incidence steadily decreased from 2005 to 2015, but showed an upturn in 2020. Stands belonging to the Atlantic region are more affected by this pest (76% of the Atlantic sampling plots affected versus just 4% of the Mediterranean plots). The species Eucalyptus globulus Labill. and monospecific stands, as well as spring precipitation of the current year were found to be positively associated with the incidence of G. platensis whereas the relationship with summer temperature of the previous year was negative. Finally, maps showing the degree of incidence over time have been produced to support decision-making for pest prevention and control. This study puts forward a methodology which allows the spread of this pest to be better understood and simulated, thus facilitating risk prevention.