Microbial Control Agents for Fungus Gnats (Diptera: Sciaridae: Lycoriella) Affecting the Production of Oyster Mushrooms, Pleurotus spp.

SIMPLE SUMMARY: Fungus gnat larvae and adults are challenging insect pests affecting the production of oyster mushrooms (Pleurotus spp.). The objectives of this study were to develop a container bioassay and assess the bacteria Bacillus thuringiensis var. israelensis (Bti) and entomopathogenic nematode Steinernema feltiae as microbial control agents against fungus gnats. We hypothesized that fungus gnat larvae and the subsequent emergence of adults would be reduced by incorporating Bti and S. feltiae into straw substrate used for producing oyster mushrooms. A series of bioassays were conducted using straw inoculated with Pleurotus columbinus and Pleurotus ostreatus. Fewer fungus gnats emerged from substrate treated with Bti compared to S. feltiae and distilled water. Steinernema feltiae was generally ineffective. Incorporating Bti and S. feltiae into the straw substrate did not appear to impede colonization by P. ostreatus. The current study indicates that Bti could be useful as a sustainable pest management technique for producing oyster mushrooms. ABSTRACT: Infestations of fungus gnats (Diptera: Sciaridae) can reduce the production of oyster mushrooms (Pleurotus spp.) grown as food crops within controlled environments. The objectives of this study were to assess the efficacy of Bacillus thuringiensis var. israelensis (Bti) and Steinernema feltiae against fungus gnat larvae. A bioassay was developed, whereby pasteurized straw was inoculated with Pleurotus columbinus and treated with Bti (Gnatrol(®)), S. feltiae (Nemashield(®)), or water. Fungus gnats (Lycoriella sp.) were released into each bioassay container for ovipositing onto the straw, thereby exposing the F(1) larvae to treated or untreated substrate. Sticky cards within the containers entrapped fungus gnats emerging from the substrate as an indicator of larval survivorship. Following three bioassays, fewer fungus gnats emerged from straw treated with Bti compared to S. feltiae and the water control. Three additional bioassays using Pleurotus ostreatus also demonstrated that fewer fungus gnats emerged from straw treated with Bti compared to S. feltiae and the untreated control. Steinernema feltiae was generally ineffective. Monitoring substrate weight in the bioassay containers over time indicated that Bti and S. feltiae did not impede colonization by P. ostreatus. Incorporating Bti into straw substrate is a promising approach for managing fungus gnats infesting Pleurotus spp.