Growth pattern of Bacillus popilliae in Japanese beetle larvae
1970
St. Julian, G. | Sharpe, E. | Rhodes, R.A.
The following is substantially the authors' abstract. Experiments in Illinois showed that induction of milky disease caused by Bacillus popilliae in 50% of the larvae of Popillia japónica Neum. by feeding requires about 109 spores/g soil. The infectious process occurs in four phases. There is an initial incubation phase of about two days during which there is no evidence of infection in the haemolymph. A vegetative phase of proliferation in the haemolymph follows and lasts until day 5, when prespores occur and a few spores are observed. This is followed by an intermediate phase lasting until day 10 and characterized by concomitant vegetative growth, prespore formation, and sporulation; maximum vegetative populations of about 109 cells/ml haemolymph occur during this phase, but the spores exceed the vegetative cells by the end of it. There is finally a sporulation phase, which terminates by day 14-21 with typical milkiness and death of larvae; vegetative populations steadily decline and large numbers of spores accumulate during this phase. Milky larvae contain an average of 5×1010 spores/ml haemolymph. Throughout the process, microscopic evidence indicated that many vegetative cells die without forming spores; dead cells disappear from the haemolymph by some unknown lytic or phagocytic process. Thus, the massive spore populations that characterize milky disease result from accumulation of spores during a prolonged period of simultaneous vegetative growth and sporulation, rather than from an extended period of exclusively vegetative growth followed by sporulation of most cells.
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