Differing infection of Isaria fumosorosea (Wize) Brown & Smith in an aphid (Myzus persicae [Sulzer]) and predatory mite (Neoseiulus cucumeris [Oudemans]) under a scanning electron microscope

Implementing a predator-mediated pathogen dissemination system can meet the goal of simultaneous biocontrol of harmful mites and other pests. But for the system to be effective, it must satisfy the requirement of high lethality of the pathogen to the target pest(s) with low lethality to predatory mites in a suitable environment. Prior testing showed that the fungal entomopathogen Isaria fumosorosea (Wize) Brown & Smith exhibited high toxicity to aphids yet low toxicity to the predatory mite Neoseiulus cucumeris (Oudemans). In practical application, the humidity conditions of conidia carried by predatory mites to plants are not necessarily constant. Therefore, we set two different humidity conditions to observe the changes of spore attachment quantity and the differences of germination and infection between predatory mites and aphids after their bodies were stained with spores. Under 50±1% relative humidity (RH), predatory mites cleaned most spores in a short time; 24 hours after dusting, the number of spores (mean ± SD) on body was (0.64±0.10)×103, just (4.43±0.35)% of that at 0h, but spores on aphids were kept (16.58±1.48)% ((6.46±0.91)×103 spores) of that at beginning. There was a significant difference in the percentage of spores retained on aphids and predatory mites (p=0.000