The lifecycle of Agrilus biguttatus: the role of temperature in its development and distribution, and implications for Acute Oak Decline

Abstract

Abstract The two spotted oak buprestid, Agrilus biguttatus Fabricus, is implicated in oak decline events across Europe, and is strongly linked to Acute Oak Decline in the U.K., although its role in the syndrome remains under investigation. In the U.K., the beetle is restricted to south and central England. The present study aimed to improve our understanding of the beetle's life history and thermal requirements, intending to explain its U.K. distribution, and to collect data for lifecycle modelling. Novel methods were developed to collect and culture the beetle in the laboratory, which enabled experiments to be carried out, providing data on the beetle's sex ratio, longevity and fecundity, and the development rates of eggs, larvae and pupae at constant temperatures. On average, females lived for 63 days and laid 82 eggs. Larvae developed through four instars. Sex ratio varied by site, with no overall trend apparent. The development rates of eggs, larvae and pupae (to adult emergence) had linear relationships with temperature, with lower developmental thresholds of 12.1, 11.9 and 15.1 °C, respectively. For each life stage, degree‐day values were calculated. Beetles appeared to have an obligatory prepupal diapause at all temperatures studied, up to and including 25 °C. The implications of the developmental findings for the beetle's current distribution, as well as the possible effects of climate change, are discussed. The beetle appears to be thermally limited in the U.K. and, if so, its distribution, and perhaps that of Acute Oak Decline, may alter under climate change.