Differential Susceptibility to High Temperature and Variation of Seasonal Occurrence between Spodoptera exigua and Plutellaxylostella

摘要

Climate change has been regarded as one of main factors to change Korean insect pest fauna. Especially, a global warming model predicts to expand habitat for insect pests originated from tropical or subtropical regions. Two insect pests, the beet armyworm {Spodoptera exigua) and the diamondback moth {Plutella xylostella), are known to overwinter in some greenhouse conditions without diapause induction in Korea. There was a clear difference between these two insects in seasonal occurrence. P. xylostella occurred only at early spring and fall seasons, but did not occur during summer. In contrast, S. exigua maintained their occurrence from late spring to fall seasons. This study set up a hypothesis that the difference in the seasonal occurrence may beresulted from variation in susceptibility to high temperature. To test the hypothesis, heat tolerance was compared between these two insects. Exposure to 42°C for 40 min killed 100% individuals of P. xylostella larvae. However, most larvae of S. exiguasurvived in response to 42 °C even for 80 min. Heat tolerance varied among developmental stages in both insects. Highest tolerant stages were 4th instar larvae and adults for P. xylostella, but 1st instai larvae for S. exigua. Pre-exposure to 37°C for30 min significandy increased heat tolerance in both insects. Induction of heat tolerance accompanied with significant increase of glycerol contents in the hemolymph in both insects and up-regulation of three heat shock protein expressions in S. exigua.These results suggest that the differential susceptibility to high temperature explains the disappearance of P. xylostella during summer, at which S. exigua maintains its occurrence.