Potential sources of sciarid and phorid infestations and implications for centralised phases I and II mushroom compost production

Mushroom production in Ireland is normally divided between compost production and mushroom cultivation. Sciarid and phorid flies are pests of mushroom cultivation but how they infest the compost is little known. This study sought to determine if compost production could be a significant source of fly pests. The sciarids, Lycoriella ingenua (Dufour), and phorids, Megaselia halterata (Wood), were found at mushroom compost production sites. Adult L. ingenua were more abundant than M. halterata in insect monitoring traps and emerging from samples of compost taken during the composting process. The limited numbers of adult M. halterata found suggest that compost production is an unlikely source of this insect pest. L. ingenua were present throughout the year, whereas M. halterata underwent a period of hibernation during December–March. Adult emergence of L. ingenua and M. halterata from compost samples was not related to adult activity recorded by insect-monitoring traps. This suggests that both L. ingenua and M. halterata are opportunists and migrate readily between suitable habitats. Considerable numbers of L. ingenua emerged from samples of pasteurised compost intended for mushroom cultivation suggesting that the compost was inadequately pasteurised or infested post-pasteurisation and conditioning.