Floral nectar versus honey dew as food for wasp parasitoids: implications for pest management in eucalypt plantations

Summary

The longevities of two species of native wasp parasitoid (Heteropelma scaposum (Morley) and Habronyx pammi (Gauld)) given floral nectar and honeydew from scale insects are compared. These parasitoids kill autumn gum moth (Mnesampela privata (Guenée)) which can outbreak in eucalypt plantations and cause considerable defoliation. The longevities of male He. scaposum given access to flowering Alyssum maritimum and Aster ‘Easter Daisy’ (both exotics) were no different from those of starved wasps. Hence, inter-row sowings of these plants in plantations on ex-pasture sites are unlikely to benefit these parasitoids. Compared to starved individuals, males of both species usually lived longer when given access to Eucalyptus globulus subsp. globulus leaves. Leaves from the previous season enabled male He. scaposum to live longer than did current season's leaves. The inference that it was honeydew on the surfaces of E. globulus subsp. globulus leaves that increased the longevities of both species of wasp was supported when Ha. pammi were found to live almost three times as long as starved wasps when provided with branchlets supporting colonies of live scale insects (Eriococcus species). The longevities of female Ha. pammi as well as males of a Pristiceros species were also increased when they were given access to branchlets with scale insect colonies. Both He. scaposum and Ha. pammi were seen feeding on honeydew in the wild (but not on flowers). Appreciating that the presence of scale insects on some plantation trees can benefit native parasitoids is in keeping with an ecologically sustainable approach to pest management.

Keywords:

• forest plantations
• insect pests
• beneficial insects
• natural enemies
• parasitoids
• interactions
• feeding behaviour
• biological control
• integrated pest management
• Eucalyptus globulus
• Australia