Wood Borer Beetle.
Is a pest of major economic importance in New Zealand, the significance of which is not adequately recognised.
Borer can weaken timber. Long-term, it can threaten the structure of parts of your home.
Borer attacks untreated and damp timber. Make sure under the floor is well ventilated to prevent this area becoming damp. For minor, or early infestation, treat the infested areas. This can be easier said than done. Replace badly affected timber.
3 – 5 mm long, dark brown / black in colour, it is clearly identifiable with the humped (hooded) prothorax which covers the head.
There are up to 7 species of borer in New Zealand. The most common is the Common House Borer. Signs that you may have borer in your home timbers, doors or furniture include small (2-4mm) flight holes on the surface of the timber and piles of fine sawdust.
The Two Toothed Longhorn borer is a native to New Zealand and also common. It is a much larger beetle and its flight holes are larger, up to 7mm, and more oval in shape. This type of borer is less likely to be found in buildings.
Common borer females lay up to 100 eggs on the surface of bare timber or in old borer holes. The eggs take 4-5 weeks to hatch and the larvae then bore into the wood, where they stay, chomping away for up to 4 years.
They then pupate before leaving the wood, creating holes. Cutting out this trapdoor is their final wood destroying act. They emerge in order to breed, will not eat any more timber and will die within 3 – 4 weeks.
The adults are airborne for about a month between November and March, to mate before the cycle starts all over again.
Two tooth borer can remain in the wood for up to 11 years before exiting in autumn. Damage is usually severe from two tooth borer and timber will often have to be replaced. Because two tooth borer will also attack living trees, they can be more common in bush clad areas.
Borer like seasoned or moist untreated timber. They are often found on the south side of buildings or in floor timbers because these areas are prone to damp. They are also fond of soft (sapwood) or untreated wood and can be common in untreated native timbers in older homes. It is not uncommon to have borer attack some boards and not others – the untouched ones are probably harder heart wood.
Some wood is naturally resistant to insect attack – for example, macrocarpa. Kiln drying radiata pine improves borer resistance. Provided it remains dry, radiata is suitable for internal framing, heart quality macrocarpa and eucalypt species for weather-exposed timbers. For piles the Building Code Acceptable Solution requires timber treated to at least H5.
Using untreated wood would require an Alternative Solution under the Building Code. Speak to your timber retailer for the best option for the intended application or see NZ Standard 3602.
Sawn timber is also more prone to borer attack than a smooth surface.
Borer-infested timber can be treated, but if timbers are severely weakened you should strengthen the timber or ultimately the timber may need to be replaced.
The only long-term treatment for borer is a residual surface application of a product including insecticide or preservative. The treatment must last longer than the lifecycle of borer. This type of treatment can only be used on bare timber, so you may need to strip the timber of paint or vanish before treatment.
Airborne treatments (such as bombs, misting or fogging) will only kill the adults on the wing (November to March) and won’t stop the larvae from eating away at the inside of your timber.
If you see evidence of borer in your weatherboards, there is a good chance the borer is more extensive than it seems. This is because borer tends to attack from the inside of the boards. The only long-term solution is to replace the affected weatherboards and treat the framing timber behind while the wall is open.
Any large-scale infestation should be treated by a professional with the right safety equipment.
Furniture can be treated by fumigation by a pest control company or by injecting the flight holes. Fumigation is not usually suitable for houses or large areas as the area needs to be completely sealed. Fumigation also doesn’t provide residual protection so you will need to consider a surface treatment as well.
Egg-Larvae 14-28 days
Larvae-pupae 2-4 years
Pupae-adult 21-60 days
Exits November – March.
Rounded holes 1 – 2 mm.
Attacks mainly soft sapwoods.
· Borer larvae are seldom, if ever, found in fresh milled timbers, but require some conditions for their development which is not present in wood until it has aged, or in some other way differs from new timber.
· When selecting a site for egg laying females appear to recognise the presence of starch in the wood, a vital ingredient for larvae survival. Eggs are NOT laid in starch free wood.
· Larvae eat and absorb cellulose only when it is rendered digestible by fungi and micro-organisms present in the wood itself and without which the borer larvae would starve.
· Humidity plays a very important part in incidence of timber infestations. Damp, humid areas create ideal conditions for borer attack.
· Most districts of NZ provide the perfect climate for borer.
· World wide distribution of borer has been effected by man himself. Primarily with the relocation of infested furniture and also the widespread use of untreated softwood timbers right through into the late 50’s and early 60’s.
· Anobium Punctatum always lays her eggs during the flight season (October – February in NZ ). Eggs are 0.55 mm long and 0.35 mm wide. Average number of eggs is 30.
· Eggs are always laid in cracks, crevices, and end grain timbers, often into old flight holes, never onto sealed, painted or varnished surfaces.
· Females may mate 3 times or more during the course of egg laying. Mating normally takes place on the surface. Sometimes this will take place with the female in the hole and the male on the surface.
· Larvae bore directly into the timber through the bottom of the egg sack. 6 mm long when fully inside the wood before eventually working to a position just below the surface (September – October in NZ ). At this point they hollow out a pupal cavity which allows for the change over form larvae through pupae and into adult beetles, climaxing with the adult beetle cutting out an exit trapdoor onto the surface.
· The exiting urge is of such magnitude that they frequently gnaw out through paints, wallpapers, varnishes, linoleums, wallboards and plasters. They have also been known to exit through sheet lead and Formica.
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