Long term changes in host plants of 'Helicoverpa punctigera' in inland Australia: Effects on migration patterns

Introduction: 'Helicoverpa punctigera' is one of two major pest Heliothine moths in Australia, the other being 'H. armigera'. 'H. punctigera' is regarded as the more migratory of the two and the best adapted to the variable and unpredictable environment of rangeland and desert regions of inland Australia. It breeds during winter on native host plants and migrates to cropping areas further east and south during the spring. There are three main habitats that support winter breeding, given favourable rains in the autumn and winter - floodplains, sandy deserts and Acacia shrublands. However, following the Millenium drought (2000 - 2009) migration has been much reduced. Methods: To determine reasons for this we analysed a database of 992 georeferenced vegetation records from 1989-2000 (pre-drought), and 846 records from 2009-2015 (post drought). These records contained information on host plant presence and were matched with Landsat EVI. Results/Conclusion: Across all three habitats there has been a decline in the abundance of good host plants for 'H. punctigera', especially in the Asteraceae, and an increase in unsuitable host plants, especially grasses. In some habitats there has been an increase in legume hosts, especially 'Cullen' spp., but these hosts are uncommon in the Acacia shrublands. The latter are located between the more distant floodplains and deserts, and the cropping areas, and would serve as a "green bridge" in spring if suitable hosts are present. We hypothesise that the lack of immigration in recent years is the result of lasting host vegetation changes following the Millenium drought.