Host plants and habitats of Helicoverpa punctigera and H. armigera (Lepidoptera: Noctuidae) in inland Australia

For Helicoverpa punctigera (Wallengren), and to a lesser extent Helicoverpa armigera (Hubner), native host plants in non-cropping regions of inland Australia are believed to be contributors to populations which migrate in spring to infest cropping regions of south-east Australia, and southwestern Australia. Non-crop hosts were sampled using sweep nets in 71 survey trips in 19 years between 1987 and 2017 for larvae of H. punctigera and H. armigera, over about 2.4 million km in inland Australia. Of 1976 samples, H. punctigera larvae were present in 50.5%, distributed throughout the study area. Larvae were found on 106 host plant species in 24 families, including 61 new host records. H. armigera larvae were found on 33 plant species from eight families, including 14 new host records. However, only 4.3% of samples were positive for this species, and they were mostly in the east of the study area and had fewer larvae than the positive H. punctigera samples. H. punctigera larvae were found in each of six habitats, being, in order of mean numbers per sample: sandy deserts > floodplains > mulga, grasslands and saltbush > stony downs. Host status was determined for both species by plotting relative incidence against relative abundance, and the good hosts for H. punctigera differed between habitats. We discuss the value and limitations of this approach for identifying key hosts in broad scale population dynamics, and primary hosts which may have close co-evolutionary histories with the insects.