Annual fluctuations in the immigrant density of rice planthoppers, Sogatella furcifera and Nilaparvata lugens (Hemiptera: Delphacidae), in the Kyushu district of Japan, and associated meteorological conditions

We analyzed overseas immigrations of rice planthoppers in Kyushu, Japan, based on trap data collected during June-July in 2000-2011. The immigrant density was high in 2006, whereas it was low in 2008 and 2011. To understand these annual fluctuations, we investigated the relationships among trap catches and the following three meteorological conditions: (1) the average temperature during January-February in North Vietnam (T-NV), where planthoppers successfully overwinter; (2) the strong upper wind from North Vietnam to South China in April-May (UWVC), when the first stage of migration occurs; (3) the strong upper wind from South China to Kyushu in June-July (UWCJ), when the second stage of migration occurs. In 2008 and 2011, T-NV values were 2.4-3.0 degrees C below the 2000-2011 average of 17.4 degrees C, and there were 9-13 fewer days with a strong upper wind (UWVC + UWCJ) in April-July compared with the 2000-2011 average of 25 days. This study showed that the rice planthopper immigrant density during the last 12 years correlated significantly with T-NV and the number of days with a strong upper wind (UWVC + UWCJ) in April-July. Thus, the meteorological conditions affected the immigrant density of rice planthoppers in Kyushu.