This document specifies a method for the determination of the preventive action of a wood preservative against recently hatched larvae of Hylotrupes bajulus (Linnaeus) when the preservative is applied as a surface treatment to wood. This method is applicable to: water-insoluble chemicals which are being studied as active insecticides; organic formulations, as supplied or as prepared in the laboratory by dilution of concentrates; organic water-dispersible formulations as supplied or as prepared in the laboratory by dilution of concentrates, and water-soluble materials, for example salts. The method is applicable whether or not the test specimens have been subjected to appropriate ageing procedures.