There are a number of borers that are pests of trees and timber in service. Correct identification is essential to determine the nature of the issue and the treatment. One genus only infests eucalypt trees and has become a major pest of timber plantations.

Would you be able to identify a Eucalyptus Longicorn?

Common name: Eucalyptus Longicorn

Scientific name(s): Phoracantha semipunctata (Australia eucalypt longicorn) the and very similar Phoracantha recurva (yellow longicorn) and other similar species (photo of Phoracantha acanthocera)

Description: Long beetles with parallel sides, densely pockmarked wing covers, and cream and brown markings. Antennae are longer than the body, reddish, and in males conspicuously barbed. Phoracantha semipunctata and recurva are up to 30mm long, but other species in the family are much larger or smaller. Larvae are up to 40mm long, yellowish-white, somewhat flattened, and have enlarged thoraxes.

Geographic distribution: Native to Australia, but Phoracantha semipunctata and P. recurva are now globally distributed especially in the tropics, wherever eucalypts are grown.

Habitat: Eucalyptus longicorns are attracted to stressed or recently dead trees or freshly cut wood, and lay eggs under loose bark. The larvae then tunnel under the bark and into the cambium layer, excavating increasingly large galleries and eventually ring barking the host trees. After 2-6 months the larvae pupate inside the tree. Adults live for a few weeks and may be attracted to house lights.

Symptoms of Phoracantha infestation include holes in the bark, stains or oozing liquid on limbs or trunks; discoloured and wilting foliage, and dieback of tree limbs. Cracked bark packed with frass is also common.

Pest status: In Australia, Phoracantha populations are limited by native parasites and parasitoids, and are unlikely to kill the host tree. Overseas, infestations can easily kill a tree within weeks, and have become a major pest in Eucalyptus plantations. They are not a pest of timber in service, although adults may emerge from recently installed infested wood in service or recently made furniture.

Treatment: Chemical insecticides are not considered suitable or effective to tree trees. Australian parasitic wasps have been used overseas, as have freshly cut trap logs to attract adult beetles. For timber in service or furniture with recent emergence, it is only necessary to repair the holes, as they do not re-infest sawn timber.

Daniel Heald, technician and entomologist.

Photo copyright Daniel Heald.

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