Acclimation effects on thermal locomotor performance of the invasive Polyphagous Shot Hole Borer beetle, Euwallacea fornicatus (Coleoptera: Curculionidae: Scolytinae)

Abstract

The Polyphagous Shot Hole Borer (PSHB; Euwallacea fornicatus, Coleoptera: Curculionidae: Scolytinae) is an invasive and destructive tree pest. To assess whether thermal acclimation influences E. fornicatus locomotion performance (i.e., induced plastic responses) that may influence invasion potential, beetles were acclimated to three temperatures (18 °C, 25 °C, and 32 °C), and four locomotion traits were measured across six temperatures (13 °C, 18 °C, 23 °C, 28 °C, 33 °C and 38 °C) per acclimation group to construct thermal performance curves, capturing critical thermal minimum (T_min), critical thermal maximum (T_max), thermal breadth (T_br), optimal performance rate (U_max). Substantial plasticity of performance curves was found in E. fornicatus. Generally, cold (18 °C) acclimation increased the thermal range of several locomotor performance traits without affecting performance levels, thereby supporting the colder-is-better hypothesis. To assess the consequences of these plastic responses, using the thermal performance curves established here, movement rates of E. fornicatus in an at-risk orchard area in South Africa were predicted across seasons while considering artificial warm and cold spells. Cold-acclimated beetles exhibited the highest cumulative distance traveled in both summer and winter, while warm-acclimated beetles had the lowest. Therefore, short-term thermal variation significantly influenced E. fornicatus locomotion performance, with cold acclimation notably improving dispersal across a wide range of thermal conditions. These findings highlight the importance of considering recent thermal history when predicting E. fornicatus invasion potential. By integrating these data with microclimatic conditions and functional models, this study offers valuable insights for predicting E. fornicatus spread, informing targeted management strategies, and refining spatially explicit risk assessments to mitigate the impacts of this invasive pest.