Photo Source: IPM Handbook
A pest of secondary importance in North America is the phorid fly. These flies are small, 1/8 inch, with a humpback appearance and very small antennae. They appear stockier than sciarids and are very active, running and hopping erratically. The males and females closely resemble each other. Adult phorids typically enter the production room and houses later in the crop cycle than sciarids. They prefer warmer air temperatures and drier conditions in the substrate. The larvae are creamy-white maggots that are no longer than 1/4 inch when fully grown. The rear end is blunt and contains the opening of the breathing tubes. The head is pointed and the same color as the rest of the body. Females enter the growing room and lay about 50 eggs in areas where there is fresh mycelia growth. The larvae hatch after several days and begin feeding. They are more sensitive to variations in compost and casing temperatures than sciarids, and the timing of the life cycle is variable. At warm compost temperatures of 75-80°F development from egg to adult may require only 15 days.
During cropping with lower temperatures (60-70°F) in the casing, development may take up to 50 days. Significantly more phorid larvae can be tolerated-perhaps as much as 50 to 100 times more than sciarids-before economic damage can occur to the crop. Phorid adults are very capable of transmitting fungal and bacterial diseases, however, and control of the adults is necessary to maintain crop health.