The Toxicity of Enzyme Fractions of Bacillus larvae1

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Abstract
A crude extract from the causal disease organism of American foulbrood, Bacillus larvae (White), is toxic when injected to honey bees (Apis mellifera L.), house flies (Musca domestica L.), milkweed bugs (Oncopeltus fasciatus (Dallas)), hide beetles (Dermestes maculatus DeGeer), and American and German cockroaches (Periplaneta americana (L.) and Blattella germanica (L.)). Oral toxicity was evident only to larvae, prepupae and adults of honey bees. Three proteolytic enzyme fractions were separated from the crude extract. One fraction, termed HI, was most toxic and was studied most intensively. Fraction II was nontoxic. The toxicity of HI appeared to be due to proteolytic activity, or at least closely associated with it. The toxin did not show great differences in effect when compared on house flies of four different strains, different ages and for sex differences. The toxicity was greater at higher temperatures. When the toxic fraction was given orally to house flies, no deleterious symptoms or mortality occurred. The loss of toxic activity occurred in the midgut and the recovered material was nonproteolytic. The nonproteolytic fractions of the crude extract from Bacillus larvae were not toxic to the test insects.

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