Official website of the New Zealand Farm Forestry Association


PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

Eucalyptus variegated beetle, August 2017

Peter Berg, New Zealand Tree Grower, August 2017.

On 8 March 2016 a eucalyptus foraging beetle new to New Zealand was collected by SPS Biosecurity as part of the forest owner’s levy funded surveillance programme. The insect, Paropsisterna variicollis, or eucalyptus variegated beetle (EVB) was found in a forest near Te Pohue, inland from Napier. Subsequently a number of other sites where EVB was present were detected and it soon became evident that it was already quite widespread.

Based upon experience in parts of Australia where the insect is native and the experience with other related species already in New Zealand, it was thought likely it would hibernate over winter – for example, in ground leaf litter or bark fissures. Preparations were made to spray around the trees, stems and foliage in infested areas with a view to attempting eradication as the insects emerged in the spring. However, new identifications in other locations continued to be made and it became apparent that the insect was not completely inactive over the Hawke’s Bay winter. By early summer further surveys confirmed the insect was quite widespread.

Not a major pest in Australia

Adult beetles on severely browsed eucalypt leaves

This became the first incursion to be managed under the Government Industry Agreement which the forest growing community had signed up to only a short time earlier. While initial demarcation surveys, monitoring and eradication attempts were directed by the Ministry for Primary Industries, incident governance and technical advisory committees were set up. The Technical Advisory Committee included experts located both within and outside New Zealand.

It was noted that EVB was not generally a major pest in commercial eucalypt plantations in Australia. However, related beetles do cause significant damage to eucalypt species in Australia, and other paropsine beetles such as Paropsis charybdis Eucalyptus tortoise beetle which are minor pests in Australia have become serious pests in New Zealand, at least partly a result of having no natural predators.

Larvae after hatching

Initially found on Eucalyptus globulus the insect was subsequently found on a number of species such as E. bosistoana, E. nitens and E. quadrangulata which have some commercial interest – particularly the more durable species. While the extent of the damage is not consistent, in a number of cases trees are quite severely defoliated and it appears that repeated attacks could prevent trees developing as well as would otherwise be the case.

Control not eradication

By early 2017 it was evident that EVB was relatively widespread in the Hawke’s Bay region and that eradication was no longer an option.Attention switched to the best forms of control and management for this pest. Among a number of proposals being considered are −

  • Looking at other vectors already introduced to control paropsines such as P. charybdis and determining if they might also be effective with EVB. For example, a parasitic wasp Ennogera nassaui gave good biological control of P. charybdis after it was released in the 1980s, although Ennogera has itself become the victim of another parasitic wasp.
  • Looking at other bio-control options specific to EVB
  • Considering spraying in accessible situations or for larger plantations
  • Improving information about preferred host species and the biology of the insect to try and find better site and species mixes to minimise the likelihood of attack by EVB. However, EVB is found in Tasmania so it is not likely we will find many situations where EVB will not survive in New Zealand.

Not detected early

Egg mass on eucalypt

The entry pathway for the insect is unknown but it seems it was a hitch-hiker from Australia because other parts of New Zealand remain free of the insect. It also appears that it was in New Zealand for some time before being identified because early detection included eggs, larvae and adult insects − a breeding population. MPI have also developed an app for mobile phones which enables rapid reporting and identification of any insects found on eucalypt species. The app encourages anyone spotting insects feeding on eucalypt leaves to record them, even if they do not appear to be one of the three species profiled. The app connects to insect experts on NatureWatch NZ to make identification. NatureWatch is an online community for nature watchers, naturalists and biodiversity experts.

The full significance of this new pest to our eucalypt plantations remains unclear, and it is also uncertain what control options might be applied. However, targeted work is now being undertaken and should provide valuable assistance in the long term.

 

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