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TWO SUSPECTS OF THE TIMBER BEETLE GAME

Dr Don Ewart takes a look at wood borers, more specifically at powder-post beetles and furniture beetles. 

Eating timber is a risky game for pests. Not all wood that looks the same is actually good to eat. That which is, has to be warm and moist over many months. Timber borers (beetles) have long been pests in Australian homes. In the 1960s and 1970s when many houses were built from green-sawn local eucalypt timbers, large beetles sometimes caused alarm when they chewed their way out through the plasterboard of a completed home.

These days, nearly all Australian reports of borers can be split neatly between the powder-post and furniture beetles. Except in Queensland, which as you know is a different place with more complex problems.

We don’t get powder-post beetles infesting pine as they need the bigger pores in hardwood to lay their eggs. Powder-post beetles tend to turn up in the sapwood bands of fresh hardwood and sometimes in starchy things from SE Asia, like furniture that wasn’t fumigated, and manufactured board. The odd dodgy batch of bamboo flooring causes big headaches, perhaps requiring an expensive kitchen rebuild. Bamboo makes for good manufactured flooring, but being a grass, if it is harvested at the wrong time of year it can be packed with starch. Starch appears to be the limiting factor for powder-post beetles and they’ll eat starchy timber to destruction, typically within five years of production.

Two common uses of hardwood continue to throw up powder-post beetle problems. The first are weatherboards delivered as radial-sawn logs, which the carpenter snaps away from a core. These have the thickest part (or base) with included sapwood and so are prone to visible borer damage as the dust (poo or more properly, ‘frass’) falls from the beetles’ exit holes and keeps coming out for many years after the beetles are done.

Both powder-post and furniture beetles tend to leave small, round exit holes. Because this is new French Oak, we know it isn’t a furniture beetle hole

The second, and thankfully becoming rarer problem, happens when the little wooden blocks of parquetry flooring are laid with sapwood in them that hasn’t been treated. There are native powder-post beetles but it is nearly always the introduced European Lyctus brunneus that does the damage we see. Where the borers are in the small sapwood bands of concealed structural timber, control is not usually attempted. If the borers are found in new decorative timbers, it is often best to see if the supplier won’t offer replacement. However, if the attack is found early enough, in a few cases it can be useful to attempt control by injecting chemical into the identified exit holes. This is slow, laborious, and won’t prevent many of the developing borers from pupating and emerging later so visible damage is ongoing for at least a while. It is an action of last resort. Furniture can be sent off for fumigation.

Furniture beetles, Anobium punctatum, are another European import. They tend to be pests of aged softwoods. It is common in the southern states for them to ‘suddenly’ trash the Baltic Pine flooring of a house that was built many decades ago. I had expected that by now, they’d have become major pests of early pine-framed housing, but it hasn’t happened. It appears that kiln drying does not artificially age the timber and may impose some increased resistance. Framing damage by furniture beetle seems to be appearing first in damp areas like the Blue Mountains and some southern coastal areas. Watch for them in old floors and generally in moist housing. Basically, we still don’t understand how they choose what is good enough to eat. Fumigation is the best control option but penetrating liquid can be used and many pyrethroid products are available.

Powder could still be tapped from the collapsing sapwood bands of this roof frame even though more than 50 years had passed since the beetles finished feeding

There are lots of other beetles, so don’t claim a species identification unless you are certain. The common names are enough for your pest management reports. If you find something larger or different that isn’t in the textbooks, take samples of the animals, the frass, take photos of the exit holes (with a scale) and get these identified.

It is reasonable business practice to handball away borer jobs. Customers are reluctant to pay full price for ongoing minor pesticide applications, so if you can’t get items fumigated, consider your potential return on effort before accepting any job. If you do want to apply a pesticide, be certain that it has the proper registration. There are few choices for powder-post beetles but if you do an APVMA label search on the family ‘Lyctidae’ you will find at least a couple of deltamethrin products with general label provisions. Whatever control is used, be it liquid insecticide, fumigation or heat or cold treatment, the timber will still need cover to prevent re-infestation. Both powder-post and furniture beetles will re-infest until the timber is destroyed. Since infestation begins when a female lands, probes and tastes, filling the exit holes and providing a good coat of oil or varnish is often enough to make her look elsewhere.

So, two dominant beetle pests but many minor species may cause confusion. The powder-post beetle eats starchy new hardwood and leaves behind conveniently powdered frass. The furniture beetle is found in old softwood and produces a gritty frass. Which is which can be determined by rubbing the frass between your fingers. Not such a hard task if you don’t mind getting a little poo on your hands.

This is a very simple introduction. To learn more about the boring beetle pests, check out my 2014 work ‘Urban timber pest beetles: risks and management’.

Dr Don Ewart

Dr Don Ewart is a termite scientist who undertakes consulting, contract research and teaches at NMIT. Dr Don chairs the termite Standard committee and is a co-author of the Code of Practice for Prior to Purchase Timber Pest Inspection. Dr Don can be found at Dr Don’s Termite Pages.