[Role of contagious infection of Pandora delphacis in suppression of Myzus persicae colonies].

The colonies of green peach aphid, Myzus persicae, on detached cabbage leaves (8 replicates) were initiated with each including 3 apterae exposed to 'spore shower' of the entomophthoraceous fungus, Pandora delphacis, to evaluate its potential for aphid control. The colonies were then allowed to freely propagate and infect from one to another for mycosis development at different regimes of temperature (10-30 degrees C) and relative humidity (74-100% RH). During a period of 30-day observation, aphid mycosis developed much more rapidly at the regimes of higher temperature (20-30 degrees C) and humidity (> or = 95% RH), at which, nymphs were effectively infected by contacting the conidia discharged from apterous cadavers. The efficacy of P. delphacis for control of M. persicae was easily visible at all regimes considered, despite variation in mycosis-caused mortality. Compared to the increase of M. persicae colony not contaminated with the fungal agent, the efficacy of control at all humidity regimes of 30 degrees C was the best, and it could be > 60% on day 4, and 100% on day 16. Secondary to the best, the increase of colony size at 20 and 25 degrees C was controlled by > 30% on day 8, and > 80% on day 20 at all the humidity regimes with occasional exceptions. The efficacy of control at 10 and 15 degrees C was usually inferior to those at higher temperatures, but to less degree associated with relative humidity. These results indicate that P. delphacis was of high potential for aphid control, deserving further study for practical utilization.