Pests that can attack seasoned hardwood timber causing structural damage are of major concern to the householder. Powderpost beetles are one of the borers found in Australia. Powderpost beetles belong to the subfamily Lyctinae in the family Bostrichidae. They are so named because their larvae can reduce susceptible timber to a fine flour-like powder
Figure 1. Larvae of powderpost beetles can reduce susceptible timber to a fine flour-like powder.
Figure 2. Adult powderpost beetle Lyctus brunneus.
Adults are up to 7 mm long, dark-brown, shiny, flattened, elongate insects (Figure 2). They have a distinct head and the terminal segments on their antennae have a clubbed appearance. Larvae are cream-coloured with brown head and jaws and 3 pairs of small jointed legs. On hatching, they are about 0.5 mm long and straight-bodied but later become C-shaped.
Biology and life cycle
Powderpost beetles are pests of the sapwood of certain hardwood timber species. Species display
minor differences in appearance, habits and longevity.
The life cycle and habits of our most common lyctine species, Lyctus brunneus, are presented below.
After mating, the female beetle seeks a suitable place for egg-laying and bites the wood, leaving a series of grooves on the surface. These tasting marks may serve to determine whether the timber contains starch, the essential larval dietary requirement, and they also expose wood pores for subsequent egg-laying. She lays into the open pores of the sapwood. Each female may lay a total of 70 eggs, with a usual limit of 3 eggs in any pore.
Eggs hatch after about 14 days and larvae feed on the starch in the sapwood until fully grown. Tunnels usually follow the grain of the wood and only the larval stage destroys timber. The development period for larvae varies from 2 to 12 months depending on temperature, humidity and the supply of starch in the sapwood. Fully-grown larvae tunnel towards the wood surface and excavate small oval cells where pupation takes place. Two to 3 weeks later, mature beetles begin to emerge through the surface of infested timber, each making a round hole (1-2 mm diameter) as it emerges. Small piles of frass associated with the emergence holes may collect on the surface of infested timber or fall nearby. Emerging adults push a small amount of frass out, but larvae moving within the sapwood also cause frass to continue to fall from emergence holes and from cracks in the timber. After emergence, the mature beetles mate and egg-laying begins. Re-infestation of timber is common and may continue until the food resource is completely utilised, usually within 4 to 5 years of felling.