Seasonal Pattern of Spodoptera litura (Lepidoptera: Noctuidae) Migration Across the Bohai Strait in Northern China

The common cutworm, Spodoptera litura (F.), is a serious crop pest with a strong migratory ability. Previous studies on the migration of S. litura were mostly carried out in its "year-round breeding region" (YBR) or "overwintering region" (OR). However, the pattern of seasonal movements in its "summer breeding region" (SBR; i.e., northern China where they cannot overwinter) remains unknown. Here, we present data from an 11-yr study of this species made by searchlight trapping on Beihuang (BH) Island in the center of the Bohai Strait, which provides direct evidence that S. litura regularly migrates across this sea. There was considerable yearly and monthly variation in the number of S. litura trapped on BH, with the vast majority trapped in the autumn. The mean time from the earliest trapping to the latest trapping within a year was 110±12 d during 2003-2013, with the shortest time span of 40 d in 2003 and the longest of 166 d in 2012. S. litura moths had downwind displacement rather than randomly by heading toward their seasonally favorable direction (i.e. toward southwest in the four autumn migration events by prevailing northeasterly winds). Some females trapped in July showed a relatively higher proportion of having mated and a degree of ovarian development, suggesting that the migration of this species is not completely bound by the "oogenesis-flight syndrome." These findings provide a good starting point of research on S. litura migration between its OR (or YBR) and SBR, which will help us develop more effective regional management strategies against this pest.