Assessment for overwintering potential of invasive and non-diapause thrips (Thysanoptera: Thripidae) by the simple cold tolerance test

Abstract

The cold tolerance, and overwintering survival and fecundity schedules in winter of female adults of the five invasive pest thrips were examined and discussed in terms of the establishment potential and geographical distribution of overwintering population at outdoor conditions on the Japanese mainland. The mortality of female thrips molting into adults at 20°C in response to chronic low temperature exposure at −5°C was examined using a lethal time (LTime) approach. Such evaluation was carried by avoiding cold shock mortality where the samples were placed according to some intervals at the sequencing: One day at 15°C, two days at 10°C, one day at 5°C, and finally one day at 0°C, before exposure them to −5°C. Thrips tabaci had the longest LT₅₀ among the five invasive thrips tested, and Frankliniella occidentalis and Hercinothrips femoralis had longer LT₅₀ with overlapping 95% limits than both Echinothrips americanus and Thrips palmi. The order of cold tolerance at −5°C is likely to match marginal areas where each species could overwinter in Japan. In addition to adult females, survival of larvae that hatched at 20°C, in response to chronic low temperature exposure at −5°C was examined for four species of them, with the same acclimatizing procedure as the adult test. The result suggested that percentages of survival of E. americanus and T. palmi were lower than those of T. tabaci and F. occidentalis at the same low temperature period tested. The rearing trials throughout several generations under semi-outdoor conditions in Kyoto City were conducted from September of 2020 to April of 2021. Under semi-outdoor conditions, F. occidentalis and T. palmi were alive until the end of March, and both laid few eggs after January onwards. On the other hand, H. femoralis and E. americanus died on mid-December and the end of February, respectively, and they had stopped laying eggs in December.