Quantitative Effects of Temperature and Exposure Duration on the Occurrence and Repair of Indirect Chilling Injury in the Fall Armyworm Spodoptera frugiperda

SIMPLE SUMMARY: The fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) is a long-distance migratory insect pest, and the invaded range of its recent expansion includes regions colder than the tropical and subtropical regions in East Asia. Adaptation to freezing and/or chilling injury during winter is required for the successful invasion and subsequent localization of newly invaded species. The mechanisms of injury caused by low temperatures are classified into three types (freezing, cold shock, and indirect chilling), and our study shows that indirect chilling injury, which is caused by the long-term exposure of insects to moderately low temperatures (3 to 15 °C), is most important for the survival of S. frugiperda during the winter. Adult S. frugiperd were more tolerant to moderately low temperatures than the larvae and pupae, but survival decreased significantly when adult S. frugiperd were exposed to temperatures of 9 °C or lower. Survival was improved by short-term daily exposure to higher temperatures, indicating the existence of a repair process for indirect chilling injury in S. frugiperd. These findings on indirect chilling injury and the repair process will improve the estimation of the potential distribution of S. frugiperd in temperate and colder regions. ABSTRACT: The fall armyworm (FAW) Spodoptera frugiperda is a long-distance migratory insect pest, and the invaded range of its recent expansion includes regions colder than the tropical and subtropical regions in East Asia. In order to understand the potential distribution of S. frugiperd in temperate and colder regions, we quantified the effects of temperature and exposure duration on the degree of indirect chilling injury caused to S. frugiperd under laboratory conditions. The adults were more tolerant to moderately low temperatures (3 to 15 °C) than the larvae and pupae. Survival decreased significantly when adult S. frugiperd were exposed to temperatures of 9 °C or lower. A time–temperature model suggested that indirect chilling injury began occurring at 15 °C. Survival was improved by short-term daily exposure to higher temperatures, indicating the existence of a repair mechanism for indirect chilling injury in S. frugiperd. The degree of repair depended on the temperature, but the relationship was not a simple direct proportion. These findings on indirect chilling injury and repair will improve the estimation of the potential distribution of S. frugiperd in temperate and colder regions.