The impact of global warming and land-use change on the pest status of rice and fruit bugs (Heteroptera) in Japan

Infestation by rice and fruit bugs (Heteroptera) became a nationwide problem in Japan in the early 1970s. Nine rice bug species and three fruit bug species have been designated as economically important. Cropping restrictions for rice produced fallow paddy fields where various rice bugs reproduced and became abundant. Plautia crossota stali, Halyomorpha halys and Glaucias subpunctatus are dominant species of fruit bug that cause damage to a range of fruit crops. However, they require cones in order to complete their life cycle. Coniferous trees planted in the 1950s bore cones after 20 years. A dry and hot summer contributes to good masting the following year and good cone production, in turn, contributes to the abundance of fruit bugs in the third year. Thus, there is strong circumstantial evidence that land-use changes were responsible for the abundance of both rice and fruit bugs during the last 30 years. Poleward range expansion was observed in Nezara viridula, Leptocorisa chinensis, G. subpunctatus and Paradasynus spinosus. A survey conducted to assess winter mortality revealed that every 1 degrees C rise in mean winter temperature resulted in a reduction of about 15% in winter mortality of N. viridula and H. halys in localities where the mean winter temperature ranges from 2 to 6 degrees C. In general, species with low developmental zero (T-0) and small thermal constant (K) show the greatest increase in annual number of generations. Species with a high T-0 for preoviposition period show the greatest increase in reproductive activity, while overwintering insects with a lower T-0 tend to appear earlier in response to the elevation of temperature. Numbers of warnings issued by the prefectures on the occurrence of rice bugs and fruit bugs were correlated. Recent global warming operates in various ways, (e.g. by increasing annual number of generations, reproductive activity and food, to produce such correlation). There are no substantial bug problems in Korea where no significant land-use changes have occurred. Rice bug outbreaks in Japan are predicted to become less frequent in the future, because there is no further scope for cropping restriction. Planting of coniferous trees has been continuously decreasing since 1970, but the area of coniferous forest is still almost the same. This suggests that the fruit bug problem will continue for the foreseeable future.