Evaluating fungus gnat (Lycoriella spp.) repellency to insecticides utilized in oyster mushroom (Pleurotus spp.) production

Fungus gnats in the genus Lycoriella have a rapid lifecycle where infestations can quickly become a nuance for farmers of many agricultural crops. In producing oyster mushrooms (Pleurotus spp.), fungus gnat larvae feed on developing mycelium and damage mushroom fruit, reducing yields, and lowering grower profits. According to the American Mushroom Institute, there are several organic insecticides compatible for use on mushrooms, but there is a lack of scientific studies to understand fungus gnat management in oyster mushroom production, specifically. In prior work, we developed a two-choice static flow olfactometer bioassay to evaluate the attractiveness of various oyster mushroom substrates. Female fungus gnats displayed attractive behavior towards inoculated straw, oyster mushroom mycelium, and oyster mushroom fruit. The growing media of pasteurized straw alone was not attractive to the gravid female fungus gnats. To build upon these results and broaden management strategy knowledge, four insecticides approved for use on mushrooms were tested for fungus gnat repellency in the established two-choice olfactometer design. The insecticides BrandtÒ EcotecÒ Plus, BotaniGardÒ, PyganicÒ, and Debug TurboÒ were tested individually by adding a small dose to oyster mushroom mycelium. Gravid female fungus gnats were provided a choice between oyster mushroom mycelium and mycelium treated with insecticide mixed according to the label rate. After 24 hours, the location of each female was recorded, and a t-test was performed to evaluate choice preference.