A Chilling Damage Index to Evaluate the Overwintering Risk of <i>Tuta absoluta</i> in Microhabitats

ABSTRACT The South American tomato pinworm, Tuta absoluta , is an important invasive pest of tomato from Europe to East Asia. Many mathematical models have been developed to predict its potential distribution range. However, T. absoluta frequently occurs in colder regions than in model predictions, probably owing to favourable microclimates. In this study, I examined the cold tolerance of T. absoluta physiologically and developed a novel indicator that can predict the overwintering risk of this moth at a microhabitat level. Survival rates of T. absoluta adults depended significantly on exposure to constant temperatures between 0°C and 10°C: &gt; 50% of adults survived 60 days at 10°C, but all adults died within 15 days at 0°C. Survival times increased significantly with 1‐h daily exposure to brief high temperatures ranging from 15°C to 25°C. On the basis of the survival data, I propose a chilling damage index ( Cd idx ) that can quantitatively evaluate the overwintering risk of adult T. absoluta from hourly temperatures in their overwintering habitats during winter. The Cd idx explained how this moth can overwinter in greenhouses in northeastern Japan, where field survey and conventional model predictions indicate that it is unlikely to overwinter in fields. Using the Cd idx to evaluate the overwintering risk of T. absoluta more accurately will help to establish efficient preventive measures against this invasive pest. The Cd idx can also be used to evaluate the overwintering risk of invasive insects in temperate and colder regions at a microhabitat level.