The first generation of the oriental armyworm, Mythimna separata (Walker), arrives every year in northern Japan in mainly late May to early June.  Analyses of weather maps suggested that this moth’s immigration source could be eastern China, but the accuracy of those analyses was very limited due to the lack of a current standard trajectory analysis.  The management of migratory insect pests such as M. separata benefits from the identification of the migration source(s) and pathway(s) of the pests.  The present study provides a trajectory analysis for M. separata.  Backward trajectories from trap sites in northern Japan were calculated with the HYSPLIT System developed by the U.S. National Oceanic and Atmospheric Administration, taking the flight speed of M. separata and the limitation of low ambient temperature at flight height into account.  The ending times of the moth’s short and long trajectories were set at dusk on the day before and two days before the possible arrival date, respectively.  The results suggested two types of possible migration pathway: a multi-step pathway from Northeast China, the Korean Peninsula, and eastern Russia, which are destination areas of the first-generation’s migration, and a direct pathway from seasonal main emigration areas in eastern China such as Jiangsu and Shandong provinces.  These findings contribute to our understanding of the migration ecology of M. separata and can be used for the development of methods to predict the migration of this insect.

The oriental armyworm, Mythimna separata (Walker) (Lepidoptera: Noctuidae), is a major migrant pest of grain in China and other Asian countries, causing huge crop production and economic losses nationwide annually.  Much of the uniquely difficult aspects of managing M. separata arises from its long-distance migratory behavior.  For example, direction and timing of winds from its overwintering regions in the south largely determine where and when large influxes of migrants arrive in the north to oviposit, making prediction of infestations difficult.  Since the 1960s, the migration routes and infestation patterns of M. separata in China have been resolved (Li et al. 1964; Jiang et al. 2011), allowing development of effective forecasting and early warning technology to help manage this insect.  Over the past two decades, large-scale outbreaks of M. separata have rarely occurred.  However, in 2012, M. separata infested much of northern and northeastern China.
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We hope that the readers will find the articles in this special focus informative and useful for oriental armyworm pest management.  We are grateful to the authors and anonymous reviewers.  We thank Editorial Board and Editor-in-Chief of the Journal of Integrative Agriculture for accepting our proposal to publish these papers.  We also thank the special fund for Agro-scientific Research in the Public Interest of China (201403031) for support of this special focus.