Migration of the Oriental Armyworm Mythimna separata in East Asia in relation to weather and climate. I. Northeastern China

Introduction The Oriental Armyworm Mythimna separata is a severe pest of cereal crops, especially wheat, maize, millet and rice, throughout eastern China. Historical records suggest that the species has been a pest on millet and wheat for thousands of years (Zou, 1956). In the northeastern provinces of Liaoning, Jilin and Heilongjiang (Fig. 4.1), where the climate is highly seasonal, with severe winters and a growing season lasting only from April to September, an initial generation of M. separata larvae regularly causes severe damage to spring wheat, millet and maize in July, and a second generation damages millet and maize, and sometimes also rice, in August. The initial infestation in the northeast arises from egg-lays by moths that appear every year, often in large numbers, in late May and early June (Chen, 1962). An intensive and comprehensive programme of research on this key pest of Chinese agriculture during the late 1950s and early 1960s prompted the proposal, in 1959, that these moths were immigrants from the south (Cai, 1990). The validity of this hypothesis was soon established and it was shown that the migrations were achieved by transport on the wind. In this chapter, we first review the earlier work on M. separata migration, and then summarise the results of a more recent research programme in which the migration has been observed directly with entomological radar. Previous research The migratory status of M. separata was demonstrated by a variety of techniques.