Dispersal of the entomopathogen Hirsutella cryptosclerotium by simulated rain

When simulated rain fell 11 m down a rain tower onto sporulating cultures or spore suspensions of Hirsutella cryptosclerotium, a pathogen of the mealybug Rastrococcus invadens, large numbers of spores and mycelial fragments were dispersed in splash droplets. Negative exponential models fitted the decreases in numbers of spores, sporecarrying droplets, and mycelium-carrying droplets with distance, and regressions of log (number) on distance accounted for more than 65% of the variance. About 50% of the droplets carrying inoculum were deposited within 10 cm of the source and none were collected beyond 40 cm. Sizes of spore-carrying and mycelium-carrying droplets did not decrease greatly with increasing distance from the source but the number of spores per droplet decreased rapidly. When the distribution of inoculum-carrying droplets with droplet size was examined, the greatest proportions of spore-carrying droplets and mycelium-carrying droplets were, respectively, in the range 200-400 and 600-800 μm, and mycelium-carrying droplets were generally larger than spore-carrying droplets.