Extreme climatic events affect populations of Asian chestnut gall wasps, Dryocosmus kuriphilus , but do not stop the spread

Global climate change affects the frequency of extreme weather events that can influence plant-insect interactions. We evaluated how the late-spring frost and severe drought that occurred in Spain in 2017 affected interactions between the invasive gall insect, Dryocosmus kuriphilus, and the native tree, Castanea sativa. We assessed effects on insect survival, fertility, population growth, and effects through changes in tree palatability and in other pests and pathogens. Late-spring frost reduced D. kuriphilus to 25-40% of previous abundance. Wasp populations recovered rapidly (>7-fold in 3 years), consistent with density-dependence in population dynamics. Larvae affected by freeze or drought were smaller. Female fecundity was affected by the freeze 1 year later. Late-spring frosts and severe drought affected leaf size and physiology. Water content was higher within galls, but nitrogen was higher within galls in non-freeze plots after weather conditions improved. Freezing also influenced the secondary chemistry of leaves. Phenol concentrations were lower, and terpenes higher, in frozen plots, while condensed tannins remained the same. Condensed tannins were reduced to half in the drought year. Freezing had limited effects on damage from other pests and pathogens. Our work expands understanding of how climate and weather affects forest pests.