Effects of Entomopathogenic Nematodes on Control of a Mushroom-infesting Sciarid Fly and on Mushroom Production

The entomopathogenic nematodes Steinernema feltiae (Biosys strain #27) and Heterorhabditis heliothidis were evaluated for the larval control of a mushroom-infesting sciarid, Lycoriella mali, and for the effects of these nematodes on mushroom (Agaricus bisporus) production. In a series of small-scale mushroom crops, infective-stage H. heliothidis and S. feltiae were applied to the mushroom casing surface in the irrigation water or incorporated into the casing material at densities ranging from 28 to 1120 and 11 to 1120 nematodes cm-2 of casing surface respectively. The mortality of L. mali larvae ranged from 52 to 100% for H. heliothidis and 38 to 100% for S. feltiae. Both nematode species reduced mycelial coverage on the casing surface at primordia initiation. Neither mushroom strain (off-white or white hybrid) or method of application (incorporation into or irrigation onto the casing surface) altered the effect on mycelial coverage. The nematodes's negative effect on mycelial growth confounded the benefit of fly control. At high nematode densities (up to 1120 nematodes cm-2), damage-free mushroom yields for the first week of harvest were less than those from the untreated control. However, at lower nematode densities, at or below 140 cm-2, the nematodes had less effect on mushroom growth, and consequently, damage-free mushroom yields for the first week of harvest were frequently greater than those from the untreated control. In the absence of flies, the first-week mushroom yield generally declined with increasing nematode densities for both white and off-white mushroom hybrids. After 4 weeks of harvest, accumulated mushroom yields had nearly recovered from the earlier decline.