Microbial Control of the Diamondback Moth, Plutella xylostella, by an Entomopathogenic Fungus, Beauveria bassiana. II. Effects of Temperature on Mycoses and Conidial Invasion Time.

In order to use an entomopathogenic fungus, Beauveria bassiana, as a microbial control agent for the diamondback moth, Plutella xylostella, the mortality patterns at various temperatures and the conidial invasion time after inoculation were investigated. When larvae were inoculated with a suspension of the B. bassiana strain MG-Bb-1 (1×107 conidia/ml), mortalities of >95% were obtained regardless of the incubation temperature. However, the longevities of infected larvae were prolonged as temperature decreased. The mean longevity±S.D. were 2.1±0.2, 2.0±0.2, 2.0±0.2, 2.8±0.4, 3.9±0.4, 5.1±0.6, 9.9±1.0, and 13.9±1.6 days at 30, 27, 25, 20, 18, 15, 11 and 7°C, respectively. The mortality patterns in larvae exposed to cycles of 25°C (12 h) and 15°C (12 h) was very similar to that in larvae reared at a constant temperature of 20°C. These results indicate that the speed of killing depends on a thermal constant. The conidial invasion into the host began approximately 7 h post-inoculation and was completed in 15 h.