Is Powder Post Beetle making a comeback?
Have you just had a new oak floor, or new oak furniture arrive and holes start appearing? Then so have a number of other people in the last few years. So read on.
Severely attacked roofing timber
Frass around emergence holes in flooring
Scored surface showing damage present
prior to cutting timber
The culprit is almost certainly the powder post beetle, Lyctus brunneus. This insect attacks the sapwood of wide pored hardwoods such as oak provided the sapwood has sufficient starch content (greater than 3%). Thus, it is clearly evident that Lyctus is a very specialised insect and has very specific requirements, especially in relation to starch. Indeed, it is the starch content of potentially susceptible hardwoods which make them susceptible to attack.
It should also be noted that as the wood ages the starch content declines due to bacterial action, etc, so that after around 10-15 years starch levels drop so that infestation/activity is no longer possible. Furthermore, given the special requirements of the insect it is not going to infest the normal old hardwood (if any) and softwoods in the house.
Given the very special requirements of the insect and the wood it attacks (newly converted wide pored hardwoods where there is sufficient starch content), then most properties will not contain such timbers except where they are introduced to form a new hardwood floor, etc. Thus it is extremely unlikely that the insect will fly into a property where such susceptible timbers have just been laid. It is almost inevitable that the insect is introduced with the wood already infected; this occurs where such wood may be stored, i e, timber yards, furniture manufacturers.
The insect seems to appear in cycles: this author has seen no significance signs of Lyctus for nearly 20 years but in the last three years 4 - 5 reports per year have been received, and he is aware of numerous other cases reported.
The female lays up to a maximum of 220 eggs; these are pushed into large vessels in exposed end grain. The larvae hatch and feed on the sapwood for one to two years. It is generally accepted that indoors the life-cycle takes around one year under normal conditions, but under ideal conditions maintained in a laboratory life cycles as short as 10 to 12 weeks have been recorded. However, maximum life cycles between 2½ years to in excess of 4 years have been reported. Thus, it is evident that environmental conditions and the nutritional condition, type of wood, etc, influence the length of the life cycle.
Adult beetles usually emerge from the infested wood between May - September. They can fly well and are attracted to light at night; during the day they hide in cracks and crevices. Beetles can often be seen emerging from infected wood and can be collected for identification. The adult beetle is dark brown in colour, somewhat elongate, 5 - 7mm in length and relatively flat.
The sapwood is often entirely disintegrated leaving only a very fine flour-like dust (frass). Where tunneling exists it tends to run parrallel with the grain.
Emergence holes are about 1-1.5 mm in diameter, and like the damage, restricted to the sapwood. Initially on upward facing surfaces the holes are surrounded by little 'volcanoes' of frass.
What action should you take?
There are several steps to consider.
The wood was inevitably supplied infected and therefore it is 'defective' and not of merchantable quality. If the wood is of aesthetic value then it may be argued that the damage (holes) make it not fit for its purpose. If one examines the wood and finds elongated surface scoring then it indicates that damage was evident when the wood was sawn and planed, ie, long before it was brought into the property.
You may therefore like to consider the following actions:
1. Ask for the wood to be replaced as it was supplied defective.
2. If damage is minor on a few sapwood edges, one can use an 'injector' can of wood preservative to squirt into the holes. If the current level of damage is acceptable then this may be an acceptible solution. Nevertheless, inform the supplier of the problem and it may be prudent to put them on notice that if it subsequently becomes worse then one should expect them to take some action over it.
3. Do not spray the whole floor! Most such floors are varnished or have some kind of finish and the preservative will not penetrate: most are also secret nailed and set on polystyrene so undersides cannot be readily treated. And, of course, to lift such a floor would be very expensive.
Finally, don't be fobbed off by the supplier with the argument, "It's nothing to do with us - you've got woodworm". This insect is inevitably brought in with the new hardwood, and it is therefore the supplier's problem.
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