The toxicity threshold of boric acid for egg larvae of Hylotrupes bajulus Linné is approx. 0.4 kg/m³ of wood (71 g B/m³) over a 12-week test period, and approx. 0.3 kg/m³ of wood (53 g B/m³) over a 6-month test period. The corresponding values for borax are 0.5-0.6 kg/m³ of wood (56-68 g B/m³) and 0.3-0.4 kg/m³ of wood (34-45 g B/m³). The values are somewhat lower in the case of the egg larvae of Anobium punctatum Degeer. Boron compounds can only be used as stomach poisons. They have a very slow effect on the larvae of both the house longhorn beetle and the common furniture beetle. Boron compounds are very effective in preventive treatments, but less well suited to curative use. Boron compounds are particularly useful in the prevention of a wide range of woodrotting fungi. No fungus is known to offer serious resistance to boron. All of the fungi investigated are killed by the application of 632 g of boron per m³ of wood. Boric acid is more effective than borax against fungi because it contains a higher proportion of boron. True dry rot dies when 55 g of sodium polyborate is applied per m² of brick wall: this represents approx. 11 g of boron per m².

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