Wood-boring insect attack.

Identifying and AssessingDamage

• Wood can be a food source for many insect species. Timber in buildings can be attacked by a range of wood-boring insects.

• Each insect has preferred timber species and some need the wood to be decayed.

• Structural weakening can result from infestation by some beetles.

Types of Wood Boring Insect

• Common furniture beetle (Anobium punctatum), ‘woodworm’

• House longhorn beetle (Hylotrupes bajulus)

• Death watch beetle (Xestobium rufovillosum)

• Lyctus powderpost beetle (Lyctus brunneus)

• Wood-boring weevil (Pentarthrum huttoni and Euophryum confine)

Common furniture beetle (‘woodworm’)

• Attacks the sapwood of all softwood and European hardwood timbers, such as oak and elm

• Infests timbers with moisture contents typical of most well ventilated roofs and suspended ground floors but such infestations are usually only of moderate severity and low activity. A severe active infestation indicates a dampness problem.

• Dies out in internal joinery, staircases and mid-floors when central heating is installed in existing buildings.

• Rarely causes structural weakening except in small-section timbers in particularly damp conditions and in the sapwood edges of floorboards which can be severely tunnelled.

Common furniture beetle (‘woodworm’)

House longhorn beetle

• Not common in the UK except in certain parts of north Surrey.

• Principally found in roof timbers, can result in structural weakening.

• Not significantly encouraged by damp conditions.

• Building Regulations requires that new roof timbers must be given suitable preservative pre-treatment.

House longhorn beetle

Death watch beetle

• Common throughout the southern half of the UK; less frequent in the north of England; unknown in Scotland except for rare cases of ‘imported’ infested timbers.

• Normally only found in buildings more than 100 years old built with hardwood timbers (eg oak and elm), although an infestation may spread into adjacent softwood timbers.

• Requires damp conditions as well as some fungal decay for establishment.

• Can cause severe damage; the structural consequences must be considered carefully.

Death watch beetle

Powderpost beetle • Causes severe damage, often reducing the sapwood to a powdered mass within two

to four years.

• Aattacks the sapwood of hardwood timbers with wide pores (eg oak, elm).

• Feeds on the starch in hardwood timbers so it dies out naturally after 10 to 15 years when the starch content is depleted. Any infestations in older timbers should be extinct.

• Does not attack softwood timbers so most modern structural timbers are unaffected.

• Infests timber components usually before delivery to site, and can remain active in these timbers after installation in the building.

• Infestation is common in plywoods manufactured from susceptible timbers.

Powderpost beetle

Wood-boring weevil

• Attacks only damp, decayed timber.

• Not a primary cause of timber deterioration, although it may increase the rate of deterioration by its tunnelling.

• Commonly attacks damp joist ends and the backs of skirting boards on damp walls.

• Dies out rapidly with drying of affected timber.

Identifying the type of damage

• Indicators of insect activity are:

freshly cut exit holes and recently ejected bore dust, although dust may have been shaken from timbers by foot traffic (eg on stairs), and

insect larvae extracted by probing the tunnelled timber. In practice, the larvae are difficult to find.

• Identification of the insect causing the damage is important, not only in deciding if any wood preservative treatment is necessary but also in deciding if any other action is needed. Table 1 identifies and classifies insect damage in building timbers into three damage categories so that unnecessary treatment can be avoided.

Table: BRE Good Repair Guide 13 Part 1 (1998)

Assessing activity and extent of damage

• Common furniture beetle

• Infestations are usually of little structural significance and therefore require little or no replacement of timber.

• Determine the extent of damage by probing with a sharp instrument to remove powdered wood.

• House longhorn beetle• Infestations commonly cause structural damage,

particularly where the timbers affected contain a large proportion of sapwood. In buildings constructed from about 1920 onwards, damage can be significant, but in older buildings where timbers tend to contain lower proportions of sapwood, the significance of damage is usually less.

• Assess damage by thorough probing, drilling or sounding as the house longhorn beetle usually leaves a sound skin of wood over the damaged timber.

Assessing activity and extent of damage

• Death watch beetle• Attack can be difficult to assess for structural damage as

it is often localised in built-in timbers, such as joist ends, or as substantial cavities deep in the centre of large timbers.

• Augment surface probing by rigorous probing of timbers where they enter potentially damp walls, by ‘sounding’ with a hammer, and by drilling or probing into large timbers showing evidence of exit holes not associated with sapwood edges.

Assessing activity and extent of damage

• Lyctus powderpost beetle• Damage by Lyctus powderpost beetle normally falls into

two categories:

• Timbers more than about 20 years old. Any infestation will be extinct. The sapwood edges of large-section hardwood beams in older properties may be damaged, but this is not generally of structural significance.

• Timbers less than 20 years old. Hardwood fittings and plywood components may be severely damaged and will usually require replacement.

Assessing activity and extent of damage

Assessing activity and extent of damage

• Wood-boring weevil• Weevil infestations of decayed damp

timber require no specific remedial measures beyond those necessary to eradicate the fungal decay. Very extensive infestations may cause temporary annoyance to building

Treatment

• Common Furniture Beetle• The usual treatment is by brush or spray

application of a liquid formulation. Pastes are also effective, but their extra cost may be justifiable only where the attack is severe and where timbers are of large dimension or of impermeable species.

• The 'treat all timbers' approach is intended to ensure that no further emergence holes will appear elsewhere.

• House Longhorn Beetle• Essential to thoroughly inspect timbers, remove all powdered sapwood and

assess the residual strength of damaged timbers.

• Expert guidance should be sought on the need for replacement (any replacement timber should be pretreated with an appropriate wood preservative).

• Remedial treatment using either organic-solvent liquid or paste is appropriate. Emulsion-based formulations are not recommended because of the potential structural consequences of continued larval activity.

• With this insect it is justifiable to completely treat all timbers in, for example, a roof or floor even if only a few members show active damage.

• DEATH WATCH BEETLE• Assess the need for replacement or repair. Special attention is required with

timbers set into external walls (such as bearing ends of beams)

• Eliminate the causes of dampness and dry out the building, together with application of an insecticide. Drier conditions alone will significantly reduce the scale of an infestation. Insecticides are normally used to speed the eradication process.

• Spraying has to be supplemented by injection into emergence holes and holes drilled into large-dimension timbers. Pastes are suitable for localised damage.

• Where there is no structural weakness insecticidal smokes can reduce the infestation. A minimum of 10 annual treatments will be required.

• Powderpost Beetle• In modern properties the presence of paint or varnish finishes on

infested items usually makes insecticidal treatments impractical and replacement of the timber is generally the more cost-effective option.

• Hardwood block or strip flooring can present particular problems in treatment, especially when laid into bitumen adhesive. Such floors are normally laid with susceptible sapwood faces to the underside, making effective insecticidal treatment almost impossible. Even if any surface finish is first removed. upper heartwood faces are usually impermeable. There is also a risk of staining as a result of leaching of the bitumen by any solvent in the treatment fluid.

• In-situ fumigation under a polyethylene sheet may be the only effective method of treating such floors.

• BRE states ‘’Organic-solvent treatments for highly active, severe infestations, where continued larval activity, even in the short term, may be structurally significant.’’

• These operate by blocking enzyme release and interfering with natural bodily function and are highly dangerous to humans.

• The ISSE therefore does not recommend the use of Organo Phosphate treatments

Alternatives to Organo Phosphate treatments

• The ISSE recommends the use of Permethrin which is obtained from members of the Chrysanthemum family but is now synthetically formulated.

• It is the basis of many flea and other insect treatments in common household use.

• It is not known to rapidly harm most mammals or birds, but is dangerously toxic to cats and fish. In general, it has a low mammalian toxicity and is poorly absorbed by skin

• All information contained in this presentation has been taken from:

• BRE Digest 327 (1993)

• BRE Digest Digest 307 (1992)