Reproduction of an arboreal aphid pest, Elatobium abietinum, is altered under drought stress

Climate change in the UK is predicted to increase both winter temperatures and the frequency of summer drought events. Elatobium abietinum, the green spruce aphid, is the most important defoliating pest of Sitka spruce, Picea sitchensis, a conifer very widely used in British forest industry. This aphid is expected to respond strongly to altered climate, with changes to population densities leading to more frequent serious outbreaks and defoliation. The impact of simulated spring-summer drought on the reproductive performance of E.abietinum was investigated under laboratory conditions. Rates were assessed under five drought treatments of differing frequencies and intensities to characterize the direction of responses under different drought scenarios, and in time-staggered trials to explore seasonal variation. Variation in the response of reproduction to water deficit was mediated by drought frequency and magnitude. Low-amplitude, moderate intermittent stress improved reproductive rates, while severe stress, both continuous and high-amplitude intermittent, had a detrimental impact when compared with observations made on well-watered controls. Season was also found to modify the response, with improvements to plant nutritional quality under high-amplitude stress reflected by improving reproduction. Despite this, no differences in rates were found during the autumn, suggesting no advancement in spruce dormancy under drought. Drought stress therefore has the potential to alter E.abietinum population densities, structure and phenology in Sitka spruce plantations, with implications for forest management, damage levels and natural control of the aphid under future altered climate.