Gumleaf skeletoniser Uraba lugens (Lepidoptera: Nolidae) larval outbreaks occur in high rainfall Western Australian jarrah (Eucalyptus marginata) forest after drought

Larvae of the gumleaf skeletoniser Uraba lugens Walker can be a severe defoliator of jarrah (Eucalyptus marginata) forest in southwest Western Australia. Extensive outbreaks that developed in the summer of 2010/2011 affected more than 250 000 ha. Rainfall or temperature anomalies correlated over large distances can be a lead to regionally synchronous population dynamics of species. These are known as Moran effects and can result in extensive outbreaks. The effects of spatial variation in regional climate (as measured by dryness index, the ratio of annual pan evaporation and annual rainfall) on the magnitude of outbreak and equilibrium populations of U. lugens were examined using long-term monitoring data. The effects of temporal variation in regional temperature and rainfall anomalies on populations were examined. The coincidence of regional rainfall and temperature anomalies with regional outbreaks was investigated using permutation multivariate analysis of variance and canonical analysis of principal coordinates. Outbreaks resulting in severe defoliation are restricted to high rainfall areas of the southern jarrah forest region in southwest Western Australia. Outbreak years were warmer than years of no known outbreak, yet temperature anomalies were a poor predictor of known multiple outbreaks. Synchronous U. lugens outbreaks coincided with a combination of long-term (seven-year) drying trends and autumn and winter drought. Canonical analysis of principal coordinates analysis using rainfall anomalies correctly predicted multiple outbreaks in 70% of cases. While the mechanisms behind drought as a driver of U. lugens outbreaks are unresolved, U. lugens outbreak may be an early indicator of future lethal stress in jarrah forest. Early insect indicators of stress are likely to allow latitude for early management responses to ameliorate effects of long-term drought on economically and ecologically important tree species.