Eucalyptus variegated beetle marching on
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Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.
From Forest health News No. 274, August 2017.
Last summer, the Australian pest Paropsisterna variicollis, usually called the eucalyptus variegated beetle (EVB) in New Zealand, was known to be infesting an area from Te Pohue in the north of Hawke’s Bay, to Te Mata Peak and the Tukituki Valley in the south (FH News 269, August 2016). Now EVB seems to be flourishing in the region, developing larger populations and spreading. Beetles have been reproducing from at least the first week of October right through until May.
Field investigations by University of Canterbury student Huimin Lin have shown extensive beetle browsing damage in Eucalyptus bosistoana, E. tricarpa, E. quadrangulata, and to a lesser extent in E. cladocalyx (all Symphyomyrtus, the largest of the seven Eucalyptus subgenera). In some cases however, it was not possible to ascertain exactly which paropsine beetles (Trachymela sloanei, Paropsis charybdis, or Paropsisterna variicollis) were responsible for the missing leaves. E. globoidea, which belongs to the Monocalyptus subgenus, seemed to be relatively free of damage. This is reassuring news for durable eucalypt growers and the New Zealand Drylands Forest Initiate (NZDFI).
EVB is known to have spread out of Hawke’s Bay as far south as Woodville at the eastern end of the Manawatu Gorge. We expect to see a fairly rapid dispersal from now on, recorded by the public, farmers and scientists alike, on the “eucalyptus leaf beetles” project, available on the Nature Watch website (naturewatch.org.nz/projects/eucalyptus-leaf-beetles-nz).
Research from Australia has shown that egg parasitoids Enoggera nassaui and Neopolycystus insectifurax, which are already established in New Zealand, can also act as biological control agents for EVB. These species are predicted to have a lower propensity to attack Paropsisterna variicollis, compared with Paropsis charybdis, but this still needs to be verified by field sampling and/or laboratory research. Predators may also play a role in regulating newly established EVB populations. The ladybird Cleobora mellyi was successfully introduced in 2013 to control psyllids and tortoise beetles on eucalypts and acacias at Ben McNeill’s farm property at Waimarama. In late summer 2017, the ladybird was thought to be preying on Paropsisterna variicollis eggs, which corroborates observations of C. mellyi browsing on Paropsisterna eggs and young larvae in Tasmania. The native Schellenberg’s soldier bug, Oechalia schellenbergii, was also observed feeding on P. variicollis larvae in November 2016. Assessing the control both parasitoids and predators exert on EVB requires active field research, and is planned for this season.
Dean Satchell (NZ Farm Forestry Association), Ben McNeill (NZDFI) and Toni Withers (Scion).
Huimin Lin’s work has been supported by the New Zealand Forest Owners Association and the Specialty Wood Products partnership.
Lin, H., Murray, T.J. & Mason, E.G., Incidence of and defoliation by a newly introduced pest, Paropsisterna variicollis (Coleoptera: Chrysomelidae), on eleven durable Eucalyptus species in Hawke’s Bay, New Zealand. N.Z. Plant Prot. 70, 45-51 (2017).
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(Scion is the trading name of the New Zealand Forest Research Institute Limited.)