Lyctine susceptibility testing and dealing with rarely susceptible hardwood species

IRG/WP 07-10607

L J Cookson, J Carr, N Chew, J W Creffield

This study examined the lyctine susceptibility of 16 timber species or hybrids. Several of the timbers have been placed previously in a ‘rarely susceptible’ category, but for standards and compliance purposes, such in-between ratings are not acceptable. Timber specimens were spot tested for starch content, and exposed to three species of lyctine beetles in an insectary. New criteria were developed to divide the problematic ‘rarely susceptible’ species, including naming a species non-susceptible if significant attack was limited to 6 mm depth, as this region is routinely lost upon sawing. Lyctine susceptible species were Erythrophleum chlorostachys, Eucalyptus delegatensis grown in Tasmania but not Victoria or NSW, Eu. regnans/obliqua hybrid, Corymbia nesophila, Eu. fibrosa, Eu. grandis, Eu. crebra, Eu. argophloia, Eu. dunnii, Eu. regnans from Tasmania, Eu. saligna, and Eu. grandis/saligna hybrid as both parent species were susceptible. The non-lyctine susceptible species were Eu. cloeziana, Eu. pilularis, Eu. sieberi, and Eu. tetradonta. Starch could be detected using the spot test in 126 of the 129 specimens rating S2 (moderate) or S3 (heavy) for lyctine attack. However, many specimens with starch were not attacked, for reasons unknown but unlikely to include narrowness of pores, for the timber species examined.

Keywords: Lyctus, lyctine, borer, hardwood sapwood, starch, Lyctus brunneus, Minthea rugicollis, Lyctus discedens, Eucalyptus, Erythrophleum, Corymbia

Conference: 07-05-20/24 Jackson, USA

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