Powderpost beetles (Lyctidae or Bostrychidae) are timber yard pests that can infest wide pored
hardwoods particularly, oak, ash, and elm before they are converted into furniture, plywood,
flooring, or construction timbers.
They can only infest the sapwood of wide pored hardwoods with a starch content above 3% and a
moisture content between 8 and 30%. The larvae of Powderpost beetles tunnel and pupate within
the sapwood band only, reducing it to powder (hence their name). While they are a lesser-known
species of wood-boring insect, they can still be found throughout the UK.
The only native species to the UK is Lyctus linearis. However, further species have arrived on our
shores hidden within infested timber such as Lyctus brunneus which came from North America in the
early 1800s. A big wave of infestations also occurred following the two world wars after large
quantities of North American hardwoods had been stored for years awaiting shipment and had
become infested.
Over subsequent decades the increasing popularity of using hardwood flooring, laminate flooring,
plywood and green oak in the home, and decorative willow wickerwork, has seen the number of
reported infestations in the UK rise.
Nicholas Donnithorne comments:
“In recent years the species I have found in products coming from the Far East have been Lyctus cavicollis and Lyctus sinensis. Correct identification is relatively tricky as it requires complete insects and the use of a high-powered microscope so that the hairs/pits on the pronotum and elytra can be examined in detail.”
What is the life cycle of the Powderpost beetle?
Powderpost beetles naturally occur in the wild. Whilst generally speaking standing trees will not be
infested by them, once wide pored hardwood trees are felled and converted into timber, the female
Powderpost beetle can detect fresh timber and fly in to lay her eggs.
- As far as it is known the female Powderpost beetle is unique among wood-boring beetles in the UK, in that once she lands on the sapwood, she will undertake quality testing before egg laying. The starch content needs to be correct (at least 3%) or she will move on. They are also unusual because they are not surface egg layers and are physically unable to do so.
- The female normally lays her eggs at night and has a specific process that ensures her eggs are laidwell away from predators. She uses an ovipositor (egg laying tube) which is the length of her body,to lay cylindrical 1mm long eggs down the early wood vessels (pores) of wide pored hardwoods, but only if the starch and moisture content is high enough for larval development. Up to 50 eggs are laid down the pores, sometimes singly, but normally in threes.
- The eggs take between 1.5 and 3 weeks to hatch, the larvae will then take from 6 to more normally 12 months to develop to the point of pupation. With a potential one-year life cycle, it is possible for an infestation to rapidly build-up.
In the UK, adult Lyctus brunneus emerge from timber from May to September. Adult beetles are 4
–7 mm in length and reddish to dark brown with a long flattened ‘rectangular’ body. All Lyctus
adults look very similar. The flight hole created by the adult as it exits the pupal chamber is circular
and 1-2mm in diameter. Adult Powderpost beetles never feed, but live for 3-6 weeks after pupation.
They happily crawl on timber surfaces and can fly, often being attracted to windows.
Treating a Powderpost beetle infestation
Outside their natural habitat, timber yards, and sawmills, Powderpost beetles are only found in
buildings and furniture where hardwoods with starchy sapwood such as the previously mentioned
oak, ash, and elm are present. Because most UK homes are constructed with softwoods such as pine
and spruce, Powderpost beetles are unlikely to cause significant structural damage to your home.
They also require very specific environmental conditions, so are unlikely to spread throughout a
property. Typically, they will cause damage to one item and then die out once all the sapwood in it
has been consumed.
Ideally, Powderpost beetle infestations need to be treated at the sawmill or timber yard. Treatment
of Powderpost beetles in homes is difficult, due to the nature of the infestation and their short life
cycle. Liquid preservatives can be used, but often there are surface finishes that will prevent useful
uptake. The removal of the sapwood, a process known as “defrassing”, is often the only quick fix for
construction timbers, and, where finished products are concerned, it is often easier to negotiate
with the supplier to replace the item. Laminates are particularly difficult to treat as the glue joints
often prevent the penetration of preservatives.
Fumigation or heat treatment of smaller items is possible and will effectively eliminate all life stages
of wood-boring insect infestations.
