This review examines recent studies of the migration of three rice planthoppers, Laodelphax striatellus, Sogatella furcifera, and Nilaparvata lugens, in East Asia. Laodelphax striatellus has recently broken out in Jiangsu province, eastern China. The population density in the province started to increase in the early 2000s and peaked in 2004. In 2005, Rice stripe virus (RSV) viruliferous rate of L. striatellus peaked at 31.3%. Since then, rice stripe disease spread severely across the whole province. Due to the migration of the RSV vectors, the rice stripe disease spread to neighboring countries Japan and Korea. An overseas migration of L. striatellus that occurred in 2008 was analyzed, when a slow-moving cold vortex, a type of low pressure system, reached western Japan from Jiangsu, carrying the insects into Japan. Subsequently the rice stripe diseases struck these areas in Japan severely. In Korea, similar situations occurred in 2009, 2011, and 2012. Their migration sources were also estimated to be in Jiangsu by backward trajectory analysis. Rice black-streaked dwarf virus, whose vector is L. striatellus, has recently re-emerged in eastern China, and the evidence for overseas migrations of the virus, just like the RSV’s migrations, has been given. A method of predicting the overseas migration of L. striatellus has been developed by Japanese, Chinese, and Korean institutes. An evaluation of the prediction showed that this method properly predicted migration events that occurred in East Asia from 2008 to 2011. Southern rice black-streaked dwarf virus (SRBSDV) was first found in Guangdong province. Its vector is S. furcifera. An outbreak of SRBSDV occurred in southern China in 2009 and spread to Vietnam the same year. This disease and virus were also found in Japan in 2010. The epidemic triggered many migration studies to investigate concrete spring-summer migration routes in China, and the addition of migration sources for early arrivals in Guangdong and Guangxi have been proposed. Nilaparvata lugens is also an important insect pest of rice. Its migration situations on the Indochina peninsula and return migrations in China are discussed.

No abstract

Species-specific changes in insecticide susceptibility were found in Asian rice planthoppers (i.e. BPH for imidacloprid and WBPH for fipronil). Insecticide resistance in BPH against imidacloprid occurred in East Asia and Indochina, but not in the Philippines. In contrast, insecticide resistance in WBPH against fipronil occurred widely in East and South-east Asia.

Species-specific insecticide resistance (imidacloprid resistance in N. lugens and fipronil resistance in S. furcifera) is ongoing in populations of the two planthoppers immigrating into Japan.

Rice planthoppers are long-distance migratory insects. The East Asian population is believed to migrate from northern Vietnam to southern China in the spring. To understand its major migration paths, a migration analysis was conducted with catch data by a single light trap located in the Red River delta in northern Vietnam. The catch data showed large peaks in late April to early May, each of which was used as a starting point of a simulation. Destination regions of simulated migrations were found to be distributed over southern Chinese provinces: Guangxi, southern Hunan, Jiangxi, northern Guangdong and northwestern Fujian. The region formed a diagonal belt stretching in the northeast direction. According to Chinese data, many planthoppers were caught in light traps along the diagonal belt region, supporting the simulation results. The planthoppers that arrive on rice plants of the early crop can multiply by one or two generations before their next emigration.

No abstract

1 A new method of backward trajectory analysis for planthopper migration is presented. The method consists of two components: an advanced weather forecast model, MM5, for weather simulation, and a migration model for trajectory calculation. The weather forecast model simulates wind fields in which trajectories are calculated by the migration model. 2 It is assumed that planthoppers, Sogatella furcifera and Nilaparvata lugens, are transported at wind speeds and in wind directions. The method is evaluated using a migration event observed at Chikugo in Japan on 25 June 1969, which was recorded in hourly catch data. 3 The results indicate that the takeoff responsible for the migration occurred at 21 UTC (Coordinated Universal Time) on 23 June along the coastal region of Fujian province in China. This is the first time that the source region of this event has been accurately identified. Determinations of the migrating duration and height are also consistent with observations. 4 Although the landing process is not considered in the model, it is shown that the method is able to simulate the migration and accurately estimate various parameters. This study also shows the importance of high-quality weather simulation.

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is an invasive pest species in the Old World. This species is originally native to the Americas. Since 2016, S. frugiperda has spread widely and rapidly throughout Africa, the Middle East, India, Southeast Asia and, most recently, to southern China. By May 2019, S. frugiperda had appeared in 13 provinces in southern China and will spread further into northern China. It is highly likely that S. frugiperda will enter Japan and Korea via overseas migrations as have many other migratory pests. To evaluate the risk of S. frugiperda invasion in Japan and the Korean Peninsula, we modelled the rate of expansion and future potential migratory range of the insect by a trajectory analytical approach using the flight behaviour of S. frugiperda and meteorological data of the past five years (2014–2018). If S. frugiperda can fly for up to 36 continuous hours over water, then our results predict migration from southern and eastern China into Japan and Korea. Most likely, Japan would be invaded from Fujian and Zhejiang in 1 June–15 July, and Kyushu, Shikoku and southwestern Honshu could face the highest risk of S. frugiperda invasion. Korea would most likely be reached by S. frugiperda from northern Zhejiang, Jiangsu, Anhui and Shandong in 1 June–15 July and later. Our results indicated a very high risk that S. frugiperda would annually invade Japan and the Korean Peninsula and cause a possible significant decrease in agricultural productivity.