The mean surface temperature rose by 1.0°C over the last 40 years in Japan. Changes in the pest status, distribution range, winter mortality, and the synchronization in phenology were examined. The increase in the number of annual generations of each taxon was predicted based on the lower developmental threshold and the thermal constant. Increasing damage due to rice‐ and fruit‐infesting bugs, their simultaneous outbreaks and the poleward geographic spread observed for six species may be triggered by global warming. The winter mortality of adults of Nezara viridula and Halyomorpha halys is predicted to be reduced by 15% by each rise of 1°C. More than 50 species of butterflies showed northward range expansions and ten species of previously migrant butterflies established on Nansei Islands during 1966–1987. Global warming may be responsible for the recent decline in abundance of Plutella xylostella and the increase in Helicoverpa armigera and Trichoplusia ni. In general, global warming may work in favour of natural enemies (except for spiders) by increasing the number of generations more than in their host species. Biological control utilizing native natural enemies is expected to become a more important control tactic in the future. Greenhouse culture may provide a model of a temperate agroecosystem after global warming. The increasing occurrence of alien species of tropical origin in association with the increase in pesticide applications might be expected. Interception of alien pests by plant quarantine followed by integrated pest management is needed.

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Summary Based on the results of five‐year study on the Nezara population, it was concluded that the level of abundance of the insect was determined partly by the combination and relative adundance of the host plants and partly by the climatic factors. The endless increase of the population was checked by the deleterious effects associated with the overpopulation which occurred locally. The degree of such overpopulation was determined by the relative abundance of host plants to the current level of the population. Therefore, even when the general level of Nezara population seemed to be low, there still exists the possibility of overpopulation in some areas. Winter was the critical period which threatened the persistence of Nezara population. The survival of the hibernating adults was partly dependent on the physiological state of adults which was determined in the period of pre‐hibernation. But when the severity of a winter exceeded the tolerance limit of the insect, the only safety‐valve which prevented the elimination of Nezara was the heterogeneity of hibernacula. Therefore,Milne's theory (1957) was closest to the known facts.