Stressful times in a climate crisis: how will aphids respond to more frequent drought?

AimAphids are abundant in natural and managed vegetation, supporting a diverse community of organisms and causing damage to agricultural crops. Using a meta-analysis approach, we aimed to advance understanding of how increased drought incidence will affect this ecologically and economically important insect group, and to characterise the underlying mechanisms. LocationGlobal. Time period1958-2020. Major taxa studiedAphids. MethodsWe used qualitative and quantitative synthesis techniques to determine whether drought stress has a negative, positive, or null effect on aphid fitness. We examined these effects in relation to 1) aphid biology, 2) the aphid-plant. species combination. We compiled two datasets: 1) a "global" dataset (n = 55 from 55 published studies) comprising one pooled effect size per study, and 2) an "expanded" dataset (n = 93) containing multiple datapoints per study, separated into different measures of aphid fitness but pooled across aphid-plant combinations. Where reported, we extracted data on the effect of drought on plant vigour, and plant tissue concentrations of nutrients and defensive compounds, to capture the potential causes of aphid responses. ResultsAcross all studies ("global" dataset), drought stress had a negative effect on aphid fitness: Hedges g = -0.57; 95% confidence interval (CI95) = {+/-}0.31. The "expanded" dataset indicated that, on average, drought stress reduced aphid fecundity (g = - 0.98; CI95 = {+/-}0.50) and increased development time (g = 1.13; CI95 = {+/-}1.02). Furthermore, drought stress had a negative impact on plant vigour (g = -7.06; CI95 = {+/-}2.86) and increased plant concentrations of defensive chemicals (g = 3.14; CI95 = {+/-}3.14). Main conclusionsAphid fitness is typically reduced under drought, associated with reduced plant vigour and increased chemical defence in drought-stressed plants. We propose a conceptual model to predict drought effects on aphid fitness in relation to plant vigour and defence.