18 - Forecasting systems for migrant pests. II. The rice planthoppers Nilaparvata lugens and Sogatella furcifera in Japan

Summary

Introduction

The long-range migrations of the the Brown Planthopper Nilaparvata lugens and the White-backed Planthopper Sogatella furcifera extend over the whole area of rice cultivation in East Asia and are closely associated with the wind systems of the monsoon climate of the region (Chapter 3, this volume). Because they do not overwinter in Japan, field populations of these planthoppers originate with overseas immigration in the Bai-u (rainy) season in June and July.

Kisimoto (1976) found that immigration of rice planthoppers into Japan was associated with the activity of frontal depressions during the Bai-u season and concluded that mass immigration was correlated with depressions that had passed through eastern central China. The southwest winds in these depressions carry the migrating planthoppers and Rosenberg & Magor (1983) used trajectory analysis to estimate the source of N. lugens arriving in Japan or caught on board ship in the East China Sea. They showed that trajectories based on winds at 1.5 km above sea level originated in potential emigration source areas more frequently than trajectories at 10 m.

Seino et al. (1987) obtained highly significant correlations between the immigration of planthoppers into Japan and the development of lowlevel jet (LLJ) airflows (see below) that coincide with the occurrence of heavy Bai-u rainfall. This chapter discusses the use of analysis of LLJs in monitoring systems to determine the location and timing of rice-planthopper immigration into Japan.