Borer library

Powderpost beetle in New Zealand hardwood

Fine, flour-like dust under a tawa floorboard or an oak chair is a different problem from the gritty dust of common house borer, and it comes from a different beetle. Before you treat anything, a borer inspection can confirm which one you have. This guide covers the powderpost beetle and where it lives.

Updated 6 October 2026

The powderpost beetle in New Zealand is Lyctus brunneus, whose grubs feed in the starch-rich sapwood of tawa, rewarewa, oak, ash and similar hardwoods. It leaves round holes 0.8–1.6 mm across and dust so fine it feels like flour. Softwoods are usually immune, so pine or rimu framing is not at risk from it.

Its life cycle usually takes about a year, much shorter than the common house borer's, so a new outbreak in a hardwood piece shows itself sooner.

What is a powderpost beetle?

Powderpost beetles are a group of small wood-boring beetles, and the species that matters in New Zealand is Lyctus brunneus. Adults are flattened, elongated and 4–7 mm long. The NZ Farm Forestry Association says it was probably native to North America and has been carried around the world in traded timber. Its larvae turn hardwood sapwood into loose, powdery dust.

The name describes the damage. The tunnels are loosely packed with very fine bore dust that can spill out of the exit holes, so small cones of pale powder on a floor or shelf are often the first thing anyone notices.

Which timbers does powderpost beetle attack in New Zealand?

Only hardwood sapwood with large enough pores and plenty of starch. Among native timbers that means tawa and rewarewa, with beech affected now and then. Imported oak, ash, elm and eucalypt are at risk too, along with bamboo. Softwoods are usually immune, so radiata pine, rimu and kahikatea framing will not carry it, and the heartwood of any species is left alone.

Powderpost risk by timber (NZFFA leaflet No. 33)
Timber	Where you may find it	Powderpost risk
Tawa	Older hardwood floors and trim	Sapwood susceptible
Rewarewa	Panelling, trim and furniture	Sapwood susceptible
Oak, ash, elm	Imported furniture and flooring	Sapwood susceptible
Eucalypt	Imported flooring and furniture	Sapwood susceptible
Bamboo	Flooring and furnishings	Susceptible
Radiata pine, rimu, kahikatea	Framing and softwood floors	Usually immune (softwood)

How do you tell powderpost damage from common house borer?

Look at hole, dust and timber as one set of evidence. Powderpost dust is very fine and smooth, like talc, where common house borer dust feels gritty. Powderpost holes are round and 0.8–1.6 mm across, a little smaller than the 1–2 mm house borer hole. Most telling is the wood itself: powderpost lives in hardwood, while the house borer's usual hosts here are rimu, kahikatea and pine.

Powderpost holes sit at the small end of the scale, beside common house borer, longhorn and huhu.

The distinction changes the advice. Powderpost in a tawa floor does not put the pine framing beneath it at risk, and borer in the framing does not explain talc-like dust in an oak table. The guide to borer in floorboards covers rimu and pine boards alongside hardwood floors.

What is the powderpost beetle life cycle?

It is usually completed in about a year, though temperature, humidity and the moisture in the wood can stretch or shorten it. Females lay their eggs inside the pores of the sapwood, the larvae feed and develop within the wood, and new adults chew their way out, usually in October and November according to the NZ Farm Forestry Association.

A one-year cycle means a fresh outbreak shows itself far sooner than common house borer, whose larvae spend three or four years in the wood. It also means a piece with no holes when you bought it can start dusting within a year or so.

Is powderpost beetle serious in a house?

In most New Zealand houses it is a limited problem, because the structure is softwood and powderpost cannot use it. The risk sits in hardwood floors, trim, furniture and stored timber, and for the piece involved it can be serious, since the sapwood is turned to powder. The NZ Farm Forestry Association advises clearing hardwood offcuts so they do not feed new infestations.

For furniture, the guide to borer in furniture and antiques covers how to deal with a piece without bringing the problem into the house. For floors, the finish matters: Consumer NZ notes that paint and varnish stop surface treatments reaching the wood, so a polished hardwood floor is harder to treat than bare timber.

Questions people ask

Will powderpost beetles spread to my house framing?

Not to softwood framing. Powderpost needs hardwood sapwood with large pores and enough starch, and radiata pine, rimu and kahikatea do not qualify. It can move between hardwood items, so an infested oak or tawa piece is best kept away from hardwood floors, trim and other furniture until it has been dealt with.

How did I get powderpost beetles?

Usually through hardwood that already carried them: a second-hand piece of furniture, reclaimed flooring, imported hardwood, or offcuts stored nearby. Because the larvae live inside the wood for most of a year, an infestation can arrive unseen and show itself only when adults emerge, usually in October and November.

What will kill powderpost beetle?

Surface products reach larvae only through bare wood, so finished furniture and floors are the hard part. Options include products made for wood-boring beetles applied to bare timber or injected into holes, following the label, and professional work on valuable pieces. The NZ Farm Forestry Association also lists kiln sterilisation and fumigation, both specialist processes rather than home jobs.

Does powderpost beetle attack rimu?

No. Rimu is a softwood, and softwoods are usually immune to powderpost. Holes in rimu floors or framing are much more likely to be common house borer or, in damp heartwood, the two-toothed longhorn. If you find very fine dust near a rimu floor, check the hardwood items close by, such as a tawa threshold or an oak table.