Powderpost beetles in Queensland timber
B.C. Peters, J. King and F.R. Wylie
Pests which can attack seasoned timber causing structural damage are of major concern to the householder. Unfortunately, the economic significance of prevention, as compared to cure, has, in the past, seldom been appreciated, but today there are signs of a different attitude being taken by manufacturers, property owners or trustees who have experienced trouble through infestation by wood-boring insects. Powderpost beetles and anobiid beetles are the main borer groups of significance in Queensland.
The biology, economic importance and management of powderpost beetles in Queensland are discussed in this publication.
Powderpost beetles
Powderpost beetles belong to the subfamily Lyctinae in the family Bostrichidae. They are so named because their larvae can reduce susceptible timber to a fine flour-like powder (Figure 1).
|
Figure 1. Larvae of powderpost beetles can reduce susceptible timber to a fine flour-like powder. |
 Figure 2. Adult powderpost
beetle Lyctus brunneus. |
Description
Adults are up to 7 mm long, dark-brown, shiny, flattened, elongate insects (Figure 2). They have a distinct head and the terminal segments on their antennae have a clubbed appearance. Larvae are cream-coloured with brown head and jaws and 3 pairs of small jointed legs. On hatching, they are about 0.5 mm long and straight-bodied but later become C-shaped.
Biology and life cycle
Powderpost beetles are pests of the sapwood of certain hardwood timber species. Species display minor differences in appearance, habits and longevity. The life cycle and habits of our most common lyctine species, Lyctus brunneus (Stevens), are presented below.
After mating, the female beetle seeks a suitable place for egg-laying and bites the wood, leaving a series of grooves on the surface. These tasting marks may serve to determine whether the timber contains starch, the essential larval dietary requirement, and they also expose wood pores for subsequent egg-laying. Using her egg-laying apparatus (ovipositor) she lays into the open pores of the sapwood. Each female may lay a total of 70 eggs, with a usual limit of 3 eggs in any pore.
Eggs hatch after about 14 days and larvae feed on the starch in the sapwood until fully grown. Tunnels usually follow the grain of the wood and only the larval stage destroys timber. The development period for larvae varies from 2 to 12 months depending on temperature, humidity and the supply of starch in the sapwood.
Fully-grown larvae tunnel towards the wood surface and excavate small oval cells where pupation takes place. Two to 3 weeks later, mature beetles begin to emerge through the surface of infested timber, each making a round hole (1-2 mm diameter) as it emerges. Unlike the damage of ambrosia beetles, these exit holes have no staining around their margins. Small piles of frass associated with the emergence holes may collect on the surface of infested timber or fall nearby. Emerging adults push a small amount of frass out, but larvae moving within the sapwood also cause frass to continue to fall from emergence holes and from cracks in the timber. After emergence, the mature beetles mate and egg-laying begins. Re-infestation of timber is common and may continue until the food resource is completely utilised, usually within 4 to 5 years of felling.
Figure 3. Various sapwood-heartwood configurations can be found in sawn timber.
Damage
It is emphasised that lyctine beetles attack only the sapwood (Figure 3) of certain hardwoods and do not attack softwoods.
Three conditions govern susceptibility: moisture content, pore size and starch content. Wood with about 15 per cent moisture content is most suitable for development of larvae. Only hardwoods have pores and lyctines attack only the sapwood of hardwood species with pores larger than the diameter of the ovipositor of the female. Susceptible timber species must also contain enough starch to nourish the developing larvae. The heartwood of hardwoods is never infested, although adults may emerge through it. Coniferous woods have different food reserves and cell structure and therefore are not susceptible. A list of timber species which are considered not susceptible to lyctines is given below (Schedule 1 of the regulations to the Timber Utilisation and Marketing Act). Under current legislation, all other species are considered susceptible. If they:
- contain starch and have not been treated against lyctines with an approved preservative treatment; or
- are being attacked by lyctines.
Most attacks take place at the saw-mill, in logs or sawn timber that are drying. Evidence of infestation may not become apparent until the timber is in-service and adults begin to emerge. Infested timber contains numerous galleries packed with fine powdery frass. The whole of the infested area may be reduced to powder leaving only a shell of wood on the outside, perforated by emergence holes. Small piles of frass may be found where a gallery has broken the surface or where an adult beetle has emerged. The frass is smooth and floury (not gritty) when rubbed between the fingers. Infestation may occur anywhere in the structure where susceptible timber has been used (for example, in subfloor areas, living space, roof space, or in furniture and artefacts). In new houses, emergence holes may appear in the lining materials (for example, in plasterboard and panelling) and joinery. Such holes are made by adults emerging from the hardwood framing beneath.
Economic species
Of the species found in Queensland, Lyctus brunneus is the most destructive and commonly encountered. Others include the small powderpost beetle Lyctus discedens Blackburn, Lyctus planicollis Le Conte, Lyctus parallelocollis Blackburn and Tristaria grouvellei Reitter. The Malayan powderpost beetle Minthea rugicollis (Walker), which was often found in rainforest hardwoods imported from South-East Asia, is now established in Queensland.
Management
In the tropical and subtropical climates of Queensland attack by powderpost beetles on susceptible timber is almost inevitable. Consumer legislation placing constraints on the sale and use of such timber was first enacted in Queensland in 1949 (the Timber Users' Protection Act) and amended in 1987 to the Timber Utilisation and Marketing Act (TUMA). Similar legislation exists in New South Wales, but not in other States.
Generally, under TUMA:
- the sale of lyctine susceptible timber is prohibited;
- the use of lyctine susceptible timber in buildings or in the manufacture of articles is an offence;
- the sale of a building or article containing susceptible timber, within 2 years of construction or manufacture, is an offence; and
- all timber sold in Queensland as impregnated with an approved preservative (immunised) at a timber-preservation plant, must carry a registered brand. Imported timber and remilled timber sold as immunised must also carry a brand.
In addition to timber immunisation, lyctine attack is prevented by the use of non-susceptible timber or by removal of the sapwood from susceptible species.
If lyctine attack is confirmed, the purchaser should determine whether the sale of the infested item or its use in a structure constitutes a breach of the Act. Note that TUMA has no provision for remedial treatments. Therefore, remedial treatment will not absolve the parties concerned from any legal liability under that legislation.
No single treatment for lyctine attack is suitable in all circumstances. The following options are available:
- In most circumstances no control measures are required because the damage is not of structural significance. For example, damage to a section of a fence paling may be of little consequence. Exit holes in plasterboard, overlying a small section of infested sapwood in the framing material, can be easily filled to restore the original appearance. However, emergences may continue for a year or longer, depending upon the amount of sapwood available for infestation. Where appearances are important, control measures may be required. For example, damage in floors or panelling may be of consequence. If lyctine damage is found in a building more than 5 years old, control measures are not usually necessary, because supplies of susceptible material should have been exhausted.
- In some cases removal of infested sapwood from affected timber may be easy. For example, sapwood can be chiselled from an infested hardwood post in a pergola.
- The replacement of affected timber with non-susceptible material may be a practical option. For example, an infested floorboard, windowsill or table leg can be replaced to remove the infestation.
- Items of furniture can be disinfested by fumigation. Small items, like carved souvenirs, are disinfested by placing them in a freezer for a week or so.
Neither fumigation nor freezing provides protection against re-infestation; however, the article can be protected by restoring the finish or by applying paint, varnish or wax polish to all exposed surfaces soon after treatment.
If further lyctine damage cannot be tolerated and other control options have been rejected, a registered residual insecticide should be used. Treatments are sprayed or brushed on to the affected parts of unfinished timber surfaces. All exposed faces of susceptible sapwood should be treated. The insecticide should be diluted in oil or water, although oil-based treatments are preferred because better penetration and persistence will be achieved. Water-based treatments leave most of the insecticide on the surface of seasoned timber. Emergence through water-based insecticide may continue for many months, but most adults will be killed as they wander over the treated surface. Immature lyctines may survive beyond the treated zone, but their emergence as adults through oil-based insecticide is unlikely. Emergence can continue through non-host materials concealing sapwood surfaces, for example, through the lining attached to ceiling battens. Both oil-based and water-based treatments provide protection from re-infestation, but additional treatment may be required depending on the persistence of the insecticide and the site of infestation. For example, hot conditions in the roof space may reduce the persistence of the chemical. Access to infested roof timbers is often difficult. In some cases, fumigation may be warranted, but protection against re-infestation is also required.
Note: In weather-exposed situations, sapwood is also susceptible to fungal decay.
Summary
Powderpost beetles attack only the sapwood of certain hardwoods and do not attack softwoods. In the tropical and subtropical climates of Queensland attack by powderpost beetles on susceptible timber is almost inevitable. The development period for larvae varies from 2 to 12 months. Re-infestation of timber is common and may continue until the food resource is completely utilised. Prevention of powderpost beetle attack is better than cure. Consumer legislation (TUMA) places constraints on the sale and use of susceptible timber. No single treatment for powderpost beetle attack is suitable in all circumstances. A range of options is available.
Source of information:
Peters, B.C., J. King, & F.R. Wylie. (1996) Pests of Timber in Queensland. Queensland Forestry Research Institute, Department of Primary Industries, Brisbane, 175 pp. Available from Queensland Government Publications
Schedule 1 of the regulations to the Timber Utilisation and Marketing Act
Timber species which are not susceptible to lyctid borer attack:
- All species of the Order Taxales.
- All species of the Order Coniferales (pines, firs, spruce etc.)
- The following species of the Division Angiospermae (hardwoods):
Trade name |
Botanical name |
Australian species |
|
|
alder, rose |
Caldcluvia australiensis |
|
almond, rose |
Owenia venosa |
|
ash, pink |
Alphitonia petriei |
|
ash, red |
Alphitonia excelsa |
|
ash, red |
Alphitonia whitei |
|
ash, silvertop |
Eucalyptus sieberi |
|
backhousia, stony |
Backhousia hughesii |
|
belah |
Casuarina cristata |
|
blackbutt |
Eucalyptus pilularis |
|
box, brush |
Lophostemon confertus |
|
box, ironwood |
Choricarpia subargentea |
|
box, ironwood |
Choricarpia leptopetala |
|
box, kanuka |
Tristantopsis laurina or |
|
|
Tristaniopsis exiliflora |
| box, swamp | Lophostemon suaveolens |
|
box, white |
Eucalyptus albens |
|
box, white-topped |
Eucalyptus quadrangulata |
|
box, yellow |
Eucalyptus melliodora |
|
gum, grey |
Eucalyptus canaliculata |
|
|
Eucalyptus major, |
|
|
Eucalyptus var. propinqua or |
|
|
Eucalyptus punctata |
|
gum, red, forest |
Eucalyptus tereticornis |
|
gum, rose |
Eucalyptus grandis |
|
gum, scribbly |
Eucalyptus
haemastoma, |
|
|
Eucalyptus signata, |
|
|
Eucalyptus racemosa or |
|
Eucalyptus rossii | |
|
hardwood, Johnstone River |
Backhousia bancroftii |
|
ironbark, silver-leaved |
Eucalyptus melanophloia |
|
karri |
Eucalyptus diversicolor |
|
mahogany, white |
Eucalyptus acmenoides, |
|
|
Eucalyptus umbra ssp. umbra or |
|
|
Eucalyptus umbra
ssp. carnea |
|
malletwood |
Rhodamnia costasta |
|
malletwood, brown |
Rhodamnia rubescens |
|
malletwood, silver |
Rhodamnia acuminata |
|
mangrove, grey |
Avicennia marina var. australasica |
|
maple, Queensland |
Flindersia brayleyana |
|
maple, scented |
Flindersia laevicarpa var. laevicarpa |
|
messmate, Gympie |
Eucalyptus cloeziana |
|
myall |
Acacia pendula |
|
oak, bull |
Allocasuarina luehmannii |
|
penda, brown |
Xanthostemon chrysanthus |
|
penda, red |
Xanthosterwn whitei |
|
penda, southern |
Xanthostemon oppositifolius |
|
penda, yellow |
Ristantia pachysperma |
|
saffronheart |
Halfordia kendack or |
|
Halfordia scleroxyla | |
|
sandalbox |
Eremophila mitchellii |
|
sassafras |
Daphnandra micrantha, |
|
Daphnandra repandula, | |
|
Doryphora aromatica or | |
|
Doryphora sassafras | |
|
sassafras, grey |
Dryadodaphne novoguineensis |
|
satinay |
Syncarpia hillii |
|
sheoak, beach |
Casuarina equisetifolia var. incana |
|
sheoak, black |
Allocasuarina littoralis |
|
sheoak, river |
Casurina cunninghamiana |
|
sheoak, rose |
Allocasuarina torulosa |
|
sheoak, swamp |
Casuarina glauca |
|
silkwood, maple |
Findersia pimenteliana |
|
stringybark, Blackdown |
Eucalyptus sphaerocarpa |
|
stringybark, white |
Eucalyptus eugenioides |
|
sycamore, silver |
Cryptocarya glaucescens |
|
tea-tree, broad-leaved |
Melaleuca leucadendra, |
|
Melaleuca quinquinervia or | |
|
Melaleuca viridiflora | |
|
tea-tree, river |
Melaleuca bracteata |
|
wattle, ironwood |
Acacia excelsa |
|
yapunyah, mountain |
Eucalyptus thozetiana |
|
yarran |
Acacia homalophylla |
Imported species |
|
|
beech, silver |
Nothofagus menziesii |
|
chengal |
Balanocarpus heimmii |
|
gaboon |
Aucoumea klaineana |
|
geronggang |
Ceratoxylon arborescens |
|
giam |
Hopea spp. |
|
kamarere |
Eucalyptus deglupta |
|
kapur |
Dryobalanops spp. |
|
malas |
Homalium foetidum |
|
planchonia or dabarima |
Planchonia spp. |
|
vitex |
Vitex cofassus |
Related DPI&F notes
Anobiid beetles in timber in Queensland
Ants in timber in Queensland
Borers and the householder in Queensland
Drywood termites in Queensland
Subterranean-termite-baiting systems
Subterranean termite infestation in buildings
Subterranean termites in Queensland
Timber Utilisation and Marketing Act 1987: Sale and use of lyctid-susceptible timber
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
Last updated 24 January 2007
