The mushroom sciarid fly, Lycoriella ingenua, benefits from its association with green mold disease (Trichoderma aggressivum) in commercial mushroom production

The mushroom fly, Lycoriella ingenua Dufour (Diptera: Sciaridae), is a pest in white button mushroom (Agaricus bisporus) farming in North America. The main risk associated with sciarid flies inside mushroom farms is that the adult can potentially vector mushroom green mold disease caused by the pathogenic fungus Trichoderma aggressivum Samuels & W. Gams (Hypocreales). Flies are attracted to T. aggressivum-infected compost and, through subsequent movement, are suspected to spread the spores. The present study evaluated whether there is a fitness benefit for the sciarid flies from their association with T. aggressivum. Lycoriella ingenua was reared on three substrates: (1) spawned mushroom compost inoculated with the T. aggressivum, (2) spawned mushroom compost and (3) unspawned mushroom compost. Developmental time from larva to adult, adult longevity, adult fecundity and female body size were used as indicators of fly fitness. There was a fitness benefit for the sciarid fly when larvae develop on spawned mushroom compost parasitized by green mold, including higher adult emergence rate, faster development time from larva to adult and larger adult females. Fly fitness declined when the compost was fully colonized by A. bisporus mycelia and T. aggressivum was not present. This suggests that sciarid larvae benefit from the T. aggressivum parasitism on A. bisporus and the green mold. Benefits may include improved nutrition, defense suppression or pre-digestion.