Prediction of the Overseas Migration of the Fall Armyworm, Spodoptera frugiperda, to Japan.

(1) Background: The fall armyworm, Spodoptera frugiperda, is an invasive migratory insect pest that first arrived in Japan in early July 2019. Since then, the species has immigrated to Japan mainly in the summer monsoon season and inflicted damage mainly on the maize used as animal feed in the western region, where major immigrations occur. In this study, to know the precise arrival timing and area of S. frugiperda for purposes of pest management, a prediction method for its overseas migration from neighboring source areas was developed. (2) Methods: The method uses the Weather Research and Forecast model to give numerical weather predictions and the GEARN-insect model to predict migration. Emigration source areas on the Chinese mainland and the island of Taiwan and the insect's take-off and flight behaviors were input to the GEARN-insect model to calculate the daily migration prediction figures. (3) Results: In a prediction evaluation using 2-year six-point trapping data in Japan, the prediction method achieved an average hitting ratio of 78%. (4) Conclusions: The method has sufficient prediction quality for operational use. The technique may be applicable to other migratory moths immigrating to Japan, such as the oriental armyworm, Mythimna separata.

Two hidden taxa in the Japanese encephalitis vector mosquito, Culex tritaeniorhynchus, and the potential for long-distance migration from overseas to Japan.

The Culex vishnui subgroups, particularly Culex tritaeniorhynchus, are considered the primary vectors of the Japanese encephalitis virus (JEV) in Asia. Recent molecular phylogenetic analyses of JEV isolates from Asian countries have shown that JEVs with diverse genetic variants are present in Asia. Furthermore, some JEV strains have been found to have crossed the East China Sea and been introduced into Japan. In this study, the possibility of overseas migration of the JE vector mosquito, Cx. tritaeniorhynchus was examined from the genetic, physical, and meteorological perspectives. Molecular phylogenetic analysis was performed based on both whole coding sequences and on the barcoding region of the mitochondrial cytochrome c oxidase subunit I (COI) gene of Cx. vishnui subgroups collected from Asian countries. Culex tritaeniorhymchus was classified into two genetically independent taxa by COI sequences: the Japanese type (Ct-J), which inhabits Japan except for the Amami Islands of southern Japan, and the continental type (Ct-C), which inhabits the Asian region except for Japan. It was confirmed that approximately 10% of Cx. tritaeniorhynchus trapped during the summer in western Kyushu were Ct-C, and that they could fly for up to 38 h continuously. The meteorological analysis also confirmed that the atmospheric flow occurring over the continent coincided with the date of Ct-C capture. This is the first report showing the existence of two taxa in Cx. tritaeniorhynchus. Their physical and physiological characteristics suggest the possibility of long-distance migration from overseas regions to Japan across the East China Sea. Future efforts are expected to provide evidence to support the occurrence of long-distance migration of Cx. tritaeniorhynchus with JEV.

Overseas immigration of fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), invading Korea and Japan in 2019.

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), spread rapidly in Africa and Asia recently, causing huge economic losses in crop production. Fall armyworm caterpillars were first detected in South Korea and Japan in June 2019. Here, the migration timing and path for FAW into the countries were estimated by a trajectory simulation approach implementing the insect's flight behavior. The result showed that FAWs found in both South Korea and Japan were estimated to have come from eastern China by crossing the Yellow Sea or the East China Sea in 10-36 h in three series of migrations. In the first series, FAW moths that arrived on Jeju Island during 22-24 May were estimated to be from Zhejiang, Anhui and Fujian Provinces after 1-2 nights' flights. In the second series, it was estimated that FAW moths landed in southern Korea and Kyushu region of Japan simultaneously or successively during 5-9 June, and these moths mostly came from Guangdong and Fujian Provinces. The FAW moths in the third series were estimated to have immigrated from Taiwan Province onto Okinawa Islands during 19-24 June. During these migrations, southwesterly low-level jets extending from eastern China to southern Korea and/or Japan were observed in the northwestern periphery of the western Pacific Subtropical High. These results, for the first time, suggested that the overseas FAW immigrants invading Korea and Japan came from eastern and southern China. This study is helpful for future monitoring, early warning and the source control of this pest in the two countries.

Dispersal of the Common Cutworm, Spodoptera litura, Monitored by Searchlight Trap and Relationship with Occurrence of Soybean Leaf Damage.

The common cutworm, Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is a major pest of soybean. Pheromone traps are used to monitor male adults, but the catch peaks do not always predict leaf damage in soybean fields. Thus, there is no accurate means of forecasting soybean damage, and insecticide is applied on the basis of farmers' observations of actual damage in fields. To understand the occurrence of soybean leaf damage, the dispersal of S. litura in a soybean field in southwestern Japan was preliminarily investigated using a searchlight trap in comparison to a pheromone trap at one location, from August to mid-October in 2016-2018. To determine the relationship between pest arrival and crop damage, trap catch numbers and the number of soybean leaves damaged by 1st-instar larvae were examined by separately comparing raw numbers and cumulative numbers. The raw catch numbers of the two trap types in August and September 2016 and 2018 preceded subsequent damage peaks by an average of 5.3 days. This temporal difference coincided with the estimated duration of the egg stage plus an assumed mating period. Furthermore, the cumulative catch numbers of the two traps in August and September were linearly associated with cumulative damaged leaves in the same period in each year and in the three-year period. The coefficient of determination (R2) of linear regression between the cumulative catch numbers of the searchlight trap and the cumulative damaged leaves for the three-year period was much higher than that between the cumulative catch of the pheromone trap and cumulative damage. This suggests that soybean leaf damage is closely linked to the number of S. litura arrivals at the survey site. Thus, the searchlight trap captured S. litura arrivals better than the pheromone trap. As the linear regression function of the cumulative catch of the searchlight trap for the three-year period was tentatively correlated with a prefectural economic injury level for soybean fields, it might be feasible to predict S. litura-induced soybean damage using searchlight traps. The cumulative female catch number of the searchlight trap was also linearly associated with damaged leaves, but the coefficient of determination was generally lower than that with the cumulative total catch. The female ratio of searchlight trap catches in September was <0.5 in contrast to S. litura migrating overseas (>0.5). The advantages and disadvantages of the two trapping methods, as well as necessary further studies are discussed. Our findings provide a foundation for S. litura monitoring with searchlight traps.

Insecticide susceptibilities of the two rice planthoppers Nilaparvata lugens and Sogatella furcifera in East Asia, the Red River Delta, and the Mekong Delta.

BACKGROUND: The two rice planthoppers, Nilaparvata lugens and Sogatella furcifera, have different life cycles in the regions of East Asia, the Red River Delta, and the Mekong Delta. The susceptibilities of these species to a range of insecticides have not previously been compared among the three regions over multiple years. Here, we describe the differences and similarities in insecticide susceptibilities of the two species among the three regions in 2006-2011. RESULTS: In all three regions in 2006 - 2011, N. lugens developed high and moderate levels of resistance to imidacloprid and thiamethoxam, respectively, but this species did not develop resistance to fipronil. In contrast, S. furcifera developed a high level of resistance to fipronil. The ranges in 50% lethal dose (LD50 ) values for N. lugens treated with both imidacloprid and thiamethoxam were similar over time between East Asia and the Red River Delta, and were different in the Mekong Delta. CONCLUSION: The results support the idea that resistant populations migrate from the Red River Delta region to East Asia. Therefore, continuous monitoring of the susceptibility of N. lugens to insecticides in the Red River Delta is very important for insecticide resistance management in East Asia. © 2017 Society of Chemical Industry.

Take-off time of the first generation of the overwintering small brown planthopper, Laodelphax striatellus in the temperate zone in East Asia.

Overseas migration of the small brown planthopper, Laodelphax striatellus (Fallén), occurs during the winter wheat harvest season in East Asia. Knowing the take-off time of emigrating L. striatellus is crucial for predicting such migrations with a simulation technique because winds, carriers of migratory insects, change continuously. Several methods were used in China and Japan from late May to early June 2012 and again in 2013 to identify the precise timing of take-off. These methods included: a tow net trap mounted to a pole at 10 m above the ground, a helicopter-towed net trap, and a canopy trap (which also had video monitoring) set over wheat plants. Laodelphax striatellus emigrated from wheat fields mainly in the early evening, before dusk. The insects also emigrated during the daytime but rarely emigrated at dawn, showing a pattern that is unlike the bimodal emigration at dusk and dawn of two other rice planthoppers, the brown planthopper, Nilaparvata lugens (Stål), and the white-backed planthopper, Sogatella furcifera (Horváth). There was no significant difference in the temporal pattern of take-off behavior between females and males of Japanese L. striatellus populations.

Insecticide susceptibilities in populations of two rice planthoppers, Nilaparvata lugens and Sogatella furcifera, immigrating into Japan in the period 2005-2012.

BACKGROUND: The brown planthopper Nilaparvata lugens and the whitebacked planthopper Sogatella furcifera are both important pests on rice throughout Asia. The major cause of recent outbreaks is thought to be the development of insecticide resistance. Thus, the authors monitored insecticide susceptibilities in populations of these two insects immigrating into Japan in the period 2005-2012. Ten insecticides were tested, including members of the organophosphate, carbamate, pyrethroid, neonicotinoid and phenylpyrazole groups. RESULTS: The LD50 values of N. lugens against imidacloprid increased from 2005 (0.7 µg g(-1)) to 2012 (98.5 µg g(-1)). The resistance ratio (LD50 value in 2012/baseline LD50 value in 1992) was 615.5. In contrast, LD50 values of N. lugens against fipronil were <1.0 µg g(-1) up to 2012, suggesting that N. lugens had developed no insecticide resistance to this insecticide. However, S. furcifera exhibited resistance against fipronil up to 2012. Except for the case of malathion, the resistances of N. lugens against members of the organophosphate and carbamate groups were closely similar in the period 2005-2012 to earlier determinations in 1984 and 1985. CONCLUSION: 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.

Migration of rice planthoppers and their vectored re-emerging and novel rice viruses in East Asia.

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.

Species-specific insecticide resistance to imidacloprid and fipronil in the rice planthoppers Nilaparvata lugens and Sogatella furcifera in East and South-east Asia.

BACKGROUND: In 2003 the development of insecticide resistance against neonicotinoids in the brown planthopper (BPH), Nilaparvata lugens (Stål) (Homoptera: Delphacidae), was first observed in Thailand and has since been found in other Asian countries such as Vietnam, China and Japan. However, the LD(50) values of BPH and the whitebacked planthopper (WBPH), Sogatella furcifera (Horváth), against both neonicotinoid and phenylpyrazole insecticides have been poorly reported in many Asian countries. RESULTS: The topical LD(50) values for imidacloprid in the BPH populations collected from East Asia (Japan, China, Taiwan) and Vietnam in 2006 were 4.3-24.2 microg g(-1) and were significantly higher than those collected from the Philippines (0.18-0.35 microg g(-1)). The BPH populations indicated a positive cross-resistance between imidacloprid and thiamethoxam. Almost all the WBPH populations from Japan, Taiwan, China, Vietnam and the Philippines had extremely large LD(50) values (19.7-239 microg g(-1) or more) for fipronil, except for several populations from the Philippines and China. CONCLUSION: 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.