8 - Insect migration in an arid continent. II. Helicoverpa spp. in eastern Australia

Summary

Helicoverpa spp. in Australia

Of the three species of Helicoverpa in Australia, two, the endemic H. punctigera and the cosmopolitan H. armigera, are major pests. In eastern Australia the two species frequently occur together, and can cause severe damage in the cropping regions of the southeast of the continent (Fig. 8.1). Summer crops affected include cotton, sunflowers, sorghum, soybeans, maize, and many vegetables and horticultural crops. Winter/spring crops include chickpeas, field peas and faba beans. It is often difficult to explain changes in the numbers of Helicoverpa spp. in the cropping areas, and this has led to speculation that immigration from non-cropping areas further inland could account for some of the discrepancies (Zalucki et al., 1986).

The pest status of Helicoverpa spp. arises from four characteristics exhibited to varying degrees by both species: high mobility, polyphagy, high fecundity and facultative diapause (Fitt, 1989). The evidence for migration in Helicoverpa spp. has been reviewed by Farrow & Daly (1987). They rated H. punctigera as the most migratory and H. armigera as the least, with the two major American pest species H. zea and Heliothis virescens intermediate.

There is compelling evidence that H. punctigera is highly migratory, and is probably an obligate migrant. Specimens of presumed Australian origin have been collected in New Zealand (Fox, 1978) and Norfolk Island (Holloway, 1977), indicating migrations of at least 2200 and 1600 km, respectively.