This fly is often a serious pest of cultivated mushrooms, although the larvae feed only on fungal mycelium and do not tunnel into the developing mushrooms (cf. Megaselia nigra, below). Minor attacks are of little or no significance but heavy infestations can cause considerable yield loss. The adult flies are sometimes a nuisance to pickers; they may also inadvertently pick up spores of Verticillium fungicola on their bodies, and then spread them from infected to previously healthy mushroom beds.
Adults occur during the summer and autumn, and are sometimes very numerous in mushroom houses, especially close to doors and lights. They often gather in considerable numbers and make characteristic jerky runs over the surface of walls, trays and boxes. In mushroom houses, most eggs are deposited in the casing material, close to the tips of the rapidly developing fungal hyphae, during the short period of mycelial growth. Under normal casing conditions, the eggs hatch in about 2 days and the larvae feed for 4-5 days before pupating; adults emerge 7-8 days later. In the lower temperatures associated with spawn-running rooms, where eggs are also deposited, development from egg to adult may take about 2 months. The adult flies often emerge in vast numbers from dumped mushroom compost and sometimes invade nearby dwellings; they may then cause considerable concern to local residents.
Adult brownish-yellow to reddish-brown, with a hump-backed appearance; antennae short and inconspicuous, with a distinctly swollen third segment; wings 1.5-2.5 mm long, without cross-veins (see Fig. 96). Egg 0.5 x 0.2mm, oval, white. Larva up to 4 mm long, creamish-white and translucent, pointed anteriorly but blunt posteriorly; anal segment with a pair of prominent spiracles and distinct papillae. Puparium 2.5 mm long, brown; anterior spiracles horn-like.
Megaselia nigra (Meigen)
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