INVESTIGATIONS OF THE MODE OF ACTION OF STRAINS OFBACILLUS CEREUSFR. AND FR. PATHOGENIC FOR THE LARCH SAWFLY,PRISTIPHORA ERICHSONII(HTG.)

Abstract

There is a significant correlation between the pathogenicity for the larch sawfly Pristiphora erichsonii (Htg.) of Bacillus cereus Fr. and Fr. strains and their respective abilities to produce lecithinase. Species of the genus Bacillus that are incapable of producing lecithinase are not pathogenic for the larch sawfly. Histopathological evidence of toxemia during the progress of B. cereus infection of the sawfly larvae is presented and it is noted that the tissue degeneration is not of the type usually associated with proteolytic or lipolytic activity. Finally, approximately three micrograms of a lecithinase preparation (containing. approximately 21 mouse LD₅₀per milligram) was found to be the LD₅₀for the fifth-instar larva of the larch sawfly. The main conclusion drawn from this evidence is that lecithinase plays an important role in the invasion and destruction of infected larch sawfly larvae.