Control of the greater and lesser wax moths (Galleria mellonella and Achroia grisella) with Bacillus thuringiensis

A commercial formulation of Bacillus thuringiensis incorporated into cold beeswax, and hence into bee combs, controlled the wax moths, Galleria mellonella and Achroia grisella, without harming the bees (Apis mellifera). Treated combs used continuously by bees remained resistant to G. mellonella after two seasons. In laboratory tests with G. mellonella, the LD50 of commercial preparations of B. thuringiensis, serotypes I or V, was 4.1 × 10−3 to 1.1 × 10−2 % dry w/w in brood comb (=1.23 × 106 to 3.5 × 106 live spores/g of brood comb). The values for A. grisella were larger. Tests with purified spores and endotoxin-crystal-enriched preparations showed that the crystal was the most important lethal factor for G. mellonella. Heat decreased the number of spores germinating in agar and also the effect of crystals against wax moths at similar rates, crystals becoming almost ineffective after 30 min at 95°C. It is not practicable therefore, to add B. thuringiensis while the wax is molten during the manufacture of comb foundation.