Natural and induced epizootics of Erynia ithacensis in mushroom hothouse populations of yellow-legged fungus gnats

Abstract

Fungal epizootics were recorded in adult populations of the yellow-legged fungus gnat, Phoradonta flavipes, in mushroom hothouses around Nanping and Sanming, Fujian Province, Southeastern China. The causal pathogen was identified as Erynia ithacensis. Relative humidity proved to be the main factor regulating the epizootic. Microhabitats with different RH caused by hothouse management practices had great impact on the level of the epizootic. An epizootic was induced successfully to the level of a natural epizootic (mortality around 14%) in healthy gnats in a nonepizootic area by introducing diseased gnat cadavers. Mortality of the gnats in an epizootic area was raised to 37% after 2 days and finally to 59% by spraying water onto such habitats as wall corners, mushroom bed racks, and ceilings.