The development of the 1983 outbreak of the common armyworm, Mythimna convecta, in eastern Australia.
A severe outbreak of Mythimna convecta throughout the cereal growing regions of eastern Australia commenced in spring 1983, 6 months after the conclusion of a nation-wide drought. The probable source areas were the grasslands of inland Australia, particularly south-west and central Queensland. Population increase occurred in a complex series of overlapping generations, some initiated directly by the drought-breaking rains, and some by isolated thunderstorms several weeks earlier in the summer. Phenological simulations suggested that M. convecta emergence occurred in early April, late May, late July and from late August to November. In each case, except for the May emergence, it is hypothesised that there were both local and long-range movements of adults on synoptic airflows, resulting in spread from several isolated sources into the grasslands of eastern Australia. Prefrontal airflows were associated with displacement to the east and south following each emergence. It is suggested that tropical troughs, associated with the 1st major rains of 1983, were responsible for concentrations in the source regions. Multitemporal Landsat data were used to establish that whilst during the drought there were very small areas of suitable habitat in the source areas, once the drought was over 36% of the area was suitable for M. convecta colonization. The subtropical grasses dried off by late winter and emigration by newly-emerged individuals on prefrontal airflows enabled the spring populations to colonize the temperate grass regions of inland New South Wales.