The development of milky disease under laboratory and field temperature regimes

The effect of temperature on the development of milky disease agent, Bacillus popilliae var. rhopaea, in third-instar Rhopaea verreauxi larvae was studied in two experiments. In the first experiment, only small differences were found between the probit lines of final percentage infection against dose under five temperature regimes (constant 18, 23, and 28°C; alternating 13–23°C, and 18–28°C). The disease developed more slowly at the lower temperatures while alternating temperatures gave shorter ET₅₀ values than the equivalent constant temperatures. In the second experiment, a higher incidence of disease was obtained under field conditions than under any of the laboratory conditions tested. It was concluded that for up to 6 months/year temperature is not likely to limit the development of B. popilliae var. rhopaea in the field, and that, under field conditions, most larvae would achieve a Phase IV infection.