Ht:>!Hintecl. from JCn.'RXAL OF lSYERTEHH,-\TE P.4.THOLOGY

Induction of milk\disease in 50% of Japanese beetle (Popillia ;apmlica) !aIT,\(' 1)\· feeding requires about IQ1l spores of Bacilllls popilliae per gram of soil. The infectious process occurs in four phases: (1) An initial incubation phase of about :2 da~'s during which there is no evidence of infection in the hemoh-mph. (2) ,-\ \'egetative phase of poJiferation in the hemolymph which lasts until c1a~' 5 when prespores occur and a few spores first are observed, (3) An intermediate phase between dav 5 and day 10 characterized b~' concomitant vegetative growth, prespore formation, and sporulation; maximum vegetative populations of about Ion ceBs per ml hemoh'mph occur during this phase but the number of spores exceed that of vegetative cells by the end of the phase. (4) Thereafter, a sporulation phase which terminates bv day 14 to day 21 with typical milkness and death of larvae: wgetative populations steadily decline and large numbers of spores accumulate during this phase. :\lilk~' larvae contain an average of 5 X 1010 spores per ml hemolYmph. Throaghout the process microscopic evidence indicates man~' wgetative ceBs die without forming spores; dead ceBs disappear from the hemolymph b~' sOllie unknown h·tic or phagocytic process. Thus the massiw spore populations which characterize milk\· disease result from accumulation of spores during a prolonged period of silllultaneous vegetative growth and spomlation rather than from an extended period of exclusiwly vegetative growth foBowed b~' sporulation of most cells.