Combined applications of an entomopathogenic fungus and a predatory mite to control fungus gnats (Diptera: Sciaridae) in mushroom production

Abstract

The fungus gnat Lycoriella auripilla Winnertz (Diptera: Sciaridae) is a key pest of mushroom production in Iran where it can be a year-round problem on commercial farms. We evaluated the entomopathogenic fungus Metarhizium anisopliae (Hypocreales: Clavicipitaceae) and the predatory soil mite, Gaeolaelaps aculeifer (Canestrini) (Mesostigmata: Laelapidae) as biocontrol agents of L. auripilla larvae when applied alone or in combination. Concentrations of M. anisopliae ranging from 103 to 108 spores/ml were tested with and without the addition of G. aculeifer in both small container trials and larger scale experiments. No mite mortality was observed in container trials with M. anisopliae and mite presence increased mortality of L. auripila larvae, more notably at lower fungal concentrations. In production scale experiments, treatments were applied just after the casing stage, and two weeks later, with very similar results. The addition of 15 mites/replicate (a basket containing 4 kg of mushroom compost) increased fungus gnat mortality significantly across all fungal concentrations, but applications of the mites alone gave a level of control comparable to the highest fungal concentration alone (108 spores/ml). Treatment with M. anisopliae at 108 spores/ml yielded an efficiency of conversion of compost into mushrooms better than untreated controls, and efficiency was even higher with the addition of G. aculeifer. However, the treatment with mites alone produced mushrooms with the same efficiency as the combined treatment, suggesting that the mites alone might be sufficient for controlling L. auripila larvae if application rates could be optimized for commercial scale production.