Northward range expansion by Nezara viridula (Hemiptera: Pentatomidae) in Shikoku and Chugoku Districts, Japan, possibly due to global warming

Field surveys and light trap catches of Nezara viridula and N. antennata (Hemiptera: Pentatomidae) in Shikoku and Chugoku Districts, Japan showed that N. viridula is now distributed along the northern coastline of Shikoku District, and in Yamaguchi Prefecture, and along the northern coastline of Shimane Prefecture, south of Izumo, Chugoku District. The present data together with previous reports suggest that the northward range expansion of N. viridula is possibly due to global warming because the monthly mean temperature for January in newly invaded areas has exceeded 5°C in recent years, for example, since 1986 in Fukuoka, below which the winter mortality of N. viridula adults becomes higher. Around the northern limit of N. viridula in Shimane Prefecture, it was not found in April-August 2008 because the monthly mean temperature for January 2008 fell below 5°C, below which the winter mortality of N. viridula becomes higher. Thus, the northern limit retreated depending on winter temperature. We confirmed the absence of N. viridula from 1979 until August 2008 in Izumo, Shimane Prefecture, and in 2007-2008 in Tottori Prefecture. Most areas along the southern seacoast in Shikoku District were occupied only by N. viridula, suggesting that it has replaced N. antennata by interspecific mating. In the Chugoku District, no area was occupied only by N. viridula, but it was more abundant than N. antennata in southern Yamaguchi Prefecture, indicating that N. viridula is now replacing N. antennata in that area.