Oriental armyworm, Mythimna separata, generally immigrate into northeastern China in late May and early June. The moths of the following generation usually emigrate in late July and August. But in certain years, moths often hang on in the local area and produce an extra generation. In this case, the summer outbreaks may occur and cause heavy damage to maize. This extra generation usually fails to return to the warm area of southern China and has less chance to survive. When and why will the summer population be detained in a deathtrap but cause serious damages? The investigations of the standard synoptic wind data and trajectory analysis gave the solutions that:
1. The monsoon climate and topography of northeastern China (the great plain is surrounded by mountains but open to south) facilitated the southern and western dominant winds (SW, S, W and NW) during summer and autumn, that prevent the moths to return southward successfully.
2. The emigration trajectories varied dramatically day by day and from place to place, but the moths eventually fell into the sea and the northern mountainous areas, where they could not survive in winter.
3. The moths would be detained to the local area in northeastern China when they were caught by the oscillations of summer monsoon or the circuitous wind systems (e.g. passage of the Northeastern cyclone and Mongolia cyclone), that made their pathways moving to and fro or circularly. It was the detained moths that constituted the outbreak populations and became victims of the pied piper effect.
Species 1: Lepidoptera Noctuidae Mythimna separata (oriental armyworm)
Keywords: migration arena, trajectory analysis
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