Developing application methods of Steinernema carpocapsae for biological control of mushroom phorid flies on mushroom farms

The mushroom phorid fly, Megaselia halterata (MPF) reduces the quality and yield of commercially grown mushrooms through larval feeding and by vectoring disease. Laboratory studies were developed to determine whether the entomopathogenic nematode Steinernema carpocapsae could infect mushroom phorid fly larvae. Nematodes were applied at the maximum recommended application rate (approximately 850 IJs/in2) to 3 g of compost containing 5 MPF larvae (second or third instars), then topped with 2 g of casing material in a 15 mL centrifuge tube. Larval mortality was observed after the tubes were incubated for 72 h (20.5 ˚C, 70% RH, 12:12 L:D). The average mortality of M. halterata was significantly higher (P < 0.05) in nematode treatments (41.5 ± 6.6 % S. E.), compared water treatments (8.0 ± 2.7 % S. E.), and negative controls (11.3 ± 3.7 % S.E.). In a second experiment, a known number of nematodes were added to 1.5 g of compost in the wells of a tissue culture plate to determine the survivability of nematodes in mushroom compost. Plates were incubated (23 ˚C, 70 % RH, 12:12 L:D) and the compost wells were washed with 20 mL of DI water every day for 10 days, and the percent of live nematodes recovered from the original population was determined. Half of the original population of nematodes survived in the mushroom compost for 4 to 5 days. These laboratory results informed the development of ongoing field studies to test application methods for S. carpocapsae on mushroom farms in Chester County, Pennsylvania.