Infestation

Common furniture beetle starts life as an egg; these are laid on a suitable timber surfaces - but some of these surfaces are cracks and crevices, end grain and, very importantly, down the old emergence holes in pupal chambers and tunnels.

The larvae hatch, bore into the sap wood when they remain causing the damage; the larvae are the feeding and growing stages and are by far the longest stage of the insect's life cycle

The spray applied timber preservative should contain a contact insecticide such as permethrin or cypermethrin. Basically all the insect has to do is to come into contact with this material - the insect doesn't have to ingest it; if it did it would also kill it. So one could theoretically argue that contact insecticide to have both stomach and contact action.

When the wood is sprayed with the preservative it penetrates the surface, probably between 2-6 mm, to leave a protective 'envelope' of insecticide. Any stages initially deluged by the fluid in the 'envelope' will be killed. Those remaining beneath the treatment will survive and continue activity. Clearly these stages will have to come into contact with the insecticidal 'envelope' at some stage for it to be effective. This occurs, at least theoretically, when (a) adults emerge, and (b) larvae hatch from surface laid eggs.