Microsatellite data collected over many of the grain growing regions of eastern Australia from December 2002 through to May 2005, has detected and described variable gene-flow years (i.e. variable levels of migration). In December 2003-February 2004 the highest proportion of regionally "local" H. armigera were observed. In contrast, in March 2003-May 2003 there were higher levels of immigration between the regions, however still not as high as those recorded in previous research (i.e. April 2001-March 2002 in Scott et al 2005b). These data provide evidence that the direction of moth movement differs from season to season, and within a season, highlighting the importance of studies in groups such as the Lepidoptera extending over consecutive years, as short-term sampling may be misleading when population dynamics and migration change so significantly.

In some years, H. armigera populations may migrate very little and then be relatively independent within each region and thus significantly influenced by local management practices. This is shown by the significant proportion of insecticide resistance developing locally (i.e. within a single growing region) in H. armigera in this research. However, there are also periods with high migration across the cropping regions, and resistance may rapidly spread at these times. This research demonstrates that insecticide resistance to several chemistries is efficiently immigrating across growing regions in seasons of moderate "migration" levels. These research results thus reaffirm the critical importance of maintaining a nationally coordinated insecticide resistance management strategy.