Evaluation of overwintering risk of tropical and subtropical insect pests in temperate regions.

Recent changes in climate and environments have promoted the range expansion of insect pests of tropical and subtropical origins into temperate regions. For more accurate and faster risk assessment of this expansion, we developed a novel indicator to link a physiologically derived parameter of chilling injury with the survival of insect populations in nature by using two insects, Spodoptera frugiperda and Cicadulina bipunctata with tropical and subtropical origins, and one cool-adapted insect, Laodelphax striatellus. The parameter derived from a proportional increment in the time to 99.9% mortality under constant low temperatures causing chilling injury evaluates the survival of target insect populations based on winter climate data. For S. frugiperda and C. bipunctata, but not for L. striatellus, the accuracy of the model in predicting the overwintering range was equivalent to, or better than, those of a conventional species distribution model. Additional field testing using S. frugiperda and comparison of the developed model with a conventional logistic model for C. bipunctata supported the validity of the indicator. These results suggest that the developed indicator will help for simple risk assessment of tropical and subtropical insect pests in temperate regions by the species distribution modelling approach.