Soil as an environment for winter survival of aphid-pathogenic Entomophthorales

The survival of Pandora neoaphidis was studied for both discharged primary conidia and hyphal bodies inside aphid cadavers after storage on moist soil at different temperatures. The activity of the inoculum was quantified by the ability to produce replicate conidia as well as the ability to infect aphids. No effect of inoculum type was found. Conidia were produced after storage for at least 32 days at 20 °C, 64 days at 10 °C, and 96 days at 5 °C. Inoculum retained the ability to initiate infections in aphids after storage for at least 14 days at 20 °C, 32 days at 10 °C, and 64 days at 5 °C. Morphological studies of the inoculum suggest that P. neoaphidis may survive unfavorable conditions as thick-walled conidia also known as loricoconidia. Furthermore, P. neoaphidis and Conidiobolus obscurus were documented for the first time in field-collected soil in early spring by baiting the soil with aphids. We hypothesize that germination of overwintering inoculum is stimulated by host-induced factors since inoculum apparently responded to the presence of aphids.