Abstract: When Studying the toxicity of Bacillus Popilliae,we found that the parasporal body used as the traditional taxonomic standard of Bacillus Popilliae was an unstable genetical structure.The parasporal body may exist or disappear as its hosts change.For example,the strain 780-1(Type A)is an original parasite on Holotrichia Oblita(Faldermann).When it is inoculated into other hosts,its parasporal body disappears;if the varied form retures to its original host,the parasporal body reappears.The strain 75P-1(Type B)is the same as type A.Therefore,the doubt about the taxonomic standard of Bacillus Popilliae has been raised.Morphological change of Bacillus Popilliae causes the change of its toxi-city.When the change takes place in the stain 780-1,its pathogenicity increases distinctly.It showes that the toxicity is independent of the parasporal body.Thus we have acquired new knowledge about the effect of the parasporal body.This corcept is of great significance in theory and practice.

Key words: Grub, Bacillus Popilliae, Morphological change