Evaluating the effectiveness of long-lasting insecticide nets for mushroom phorid fly management

The mushroom phorid fly, Megaselia halterata, is a significant pest of cultivated mushrooms. Its larvae feed on mushroom mycelia, and adults spread diseases, thereby reducing yield. Conventional pesticide usage harms mushroom mycelia and may leave residues, highlighting the need for safer alternatives. Mushroom growers typically conduct post-crop pasteurization using steam or steam with sanitizers to clean growing rooms and prevent contamination of future crops. Long-lasting insecticide nets (LLINs) have been reported as effective in managing agricultural insect pests both in pre- and post-harvest systems. Previous laboratory studies testing the efficacy of different LLIN prototypes against M. halterata identified Mushroom protector® containing deltamethrin and the synergist piperonyl butoxide as the most promising, with >90% initial mortality and sustained >70% mortality over seven months. Here, we present results from laboratory evaluation of Mushroom protector® LLIN against M. halterata adults.  First, we conducted a residual exposure bioassay where flies were exposed to LLIN for varying durations, and the percentage mortality recorded to determine the duration required to acquire a lethal insecticidal dosage. Second, flies were exposed at 3-, 5-, and 7-days post-steam to LLINs that were steamed for 24h prior, to investigate the effect of post-crop pasteurization on the efficacy of the LLIN.  Our results show significantly higher mortality rates compared to the controls. Additionally, steaming did not affect the effectiveness of LLIN. These findings will have implications for the development of integrated pest management strategies for M. halterata, with the potential to improve mushroom yield and quality.