Persistence of Bacillus thuringiensis in foundation beeswax and beecomb in beehives for the control of Galleria mellonella

Beecomb was protected against wax moth attack by impregnating foundation beeswax with Bacillus thuringiensis. Bakthane, a serotype I product, gave good protection of broodcomb for 2 yr at 0.5% in wax and partial protection for 6 yr at 2%. The active component was exotoxin present at about 0.9% in Bakthane in a very insoluble state. No harm to the bees was detected, even when a partially purified preparation of exotoxin was used, but further tests on the leaching of pure exotoxin from comb into honey are required before the latter can be regarded as a practical method of wax moth control. The action of exotoxin on Galleria mellonella larvae was slower than that of the spore-crystal complex and less than that of exotoxin on some Diptera. Spores and crystals of serotype V were × 500 as potent in G. mellonella as those of serotype I and exotoxin on honey-rich artificial food in laboratory assays, but their activity deteriorated in the first hive trials with treated foundation wax. Prehive deterioration was due both to Teepol and soap in the liquid lubricating the wax mill rollers and to moist storage of the foundation. This deterioration was prevented by the use of Triton X-100 as lubricant, by drying the newly impregnated foundation wax and by storing it in dry conditions. This resulted in good protection of comb for one hive season by 1% of serotype V Thuricide in foundation wax. However, protection after two seasons varied, making the use of serotype V spores and crystals uneconomical for commercial practice, although safe for bee and man.