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

Abstract

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 (UW_VC), when the first stage of migration occurs; (3) the strong upper wind from South China to Kyushu in June–July (UW_CJ), when the second stage of migration occurs. In 2008 and 2011, T _NV values were 2.4–3.0 °C below the 2000–2011 average of 17.4 °C, and there were 9–13 fewer days with a strong upper wind (UW_VC + UW_CJ) 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 (UW_VC + UW_CJ) in April–July. Thus, the meteorological conditions affected the immigrant density of rice planthoppers in Kyushu.

Appendix

 

• 1. Relational expression for the first stage of emigrations from North Vietnam to South China during April and May

  The total number of planthoppers as the i-th emigrants in North Vietnam can be described using the following relational expression (1), because they are directly proportional to the product of OW^Vietnam (the number of successfully overwintered planthoppers) and G ^Vietnam (the population growth rate in North Vietnam, considering the effects of parameters such as temperature and pesticide application):

  $$ \mathop \sum \limits_{i} {\text{EM}}_{i}^{{ {\text{Vietnam}}}} \propto {\text{OW}}^{\text{Vietnam}} {G}^{\text{Vietnam}}. $$

  (1)

• 2. Relational expression for the first stage of immigration into South China from North Vietnam during April and May

  The total number of immigrants into major destination regions in the first stage of migration in South China (IM^{South China}) can be described using the following relational expression (2), considering the rate of successful long-distance migration and subsequent landing on the ground for the i-th emigration (R ^{1st migration} _i ):

  $$ {\text{IM}}^{\text{South\;China}} = \mathop \sum \limits_{i} {\text{EM}}_{i}^{{ {\text{Vietnam}}}} R_{i}^{{ 1 {\text{st\;migration}}}}. $$

  (2)

• 3. Relational expression for the second stage of emigrations from South China to Kyushu during June and July

  The total number of planthoppers as the i-th emigrants in South China can be described using the following relational expression (3), because they are directly proportional to the product of IM^{South China} and G ^{South China} (population growth rate in South China, considering the effects of parameters such as temperature and pesticide application):

  $$ \mathop \sum \limits_{i} {\text{EM}}_{i}^{{\text{South\;China}}} \propto {\text{IM}}^{\text{{South\;China}}} G^{{\text{South\;China}}}. $$

  (3)

• 4. Relational expression for the second stage of immigration into Kyushu from South China during June and July

  The total number of immigrants into Kyushu (IM^Kyushu) can be described using the following relational expression (4), considering the rate of successful transoceanic migration and subsequent landing on the ground in the i-th emigration (R ^{2nd migration} _i ):

  $$ {\text{IM}}^{\text{Kyushu}} = \mathop \sum \limits_{i} {\text{EM}}_{i}^{\text{South\;China}} R_{i}^{{ 2 {\text{nd\;migration}}}}. $$

  (4)