The discovery in 1951, of siricid wood wasps in Baltic pine imported from Czechoslovakia, initiated research in to the problem of sterilizing large stocks of block-stacked timber in situ, and a result it was found that atmospheric fumigation by methyl bromide provides a very effective alterative to the usual method of sterilizing timber by heating in a kiln. This is particularly advantageous if the amount of timber to be treated is very large. The number of kilns available at any center for such work is relatively small, and not only is there usually some delay in the treatment of large quantities of timber, but the cost of transport is also considerable.