Influence of the entomopathogenic nematode Steinernema carpocapsae infected host cadavers or their extracts on the foliar nematode Aphelenchoides fragariae on Hosta in the greenhouse and laboratory

The influence of entomopathogenic nematode Steinernema carpocapsae infected wax moth, Galleria mellonella, cadavers and their extracts on the foliar nematode Aphelenchoides fragariae on hosta was studied in the greenhouse. Curative application of both cadavers and their extracts (prepared by crushing cadavers in water) in 1999 and only cadaver extract in 2000 significantly reduced A. fragariae numbers in leaves compared to the control 30 and 45 days after treatment (DAT). Both the cadavers and their extracts significantly reduced A. fragariae numbers in potting medium as compared to the control within 15, 30, and 45 DAT in both years. Preventively applied cadavers also significantly reduced A. fragariae numbers in leaves compared to the control in 2001 but not in 2002. In both years, the numbers of A. fragariae infected leaves per plant decreased in the preventive cadaver treatment compared with the control. Preventively applied cadavers significantly reduced A. fragariae numbers in the potting medium compared to the control at 30 DAT in 2002 and 150 DAT in 2001. Dead (crushed or autoclaved) S. carpocapsae caused significant mortality at 4 and 8 DAT but live S. carpocapsae had no detrimental effect on A. fragariae in water suspension. Both S. carpocapsae infected cadavers and their extracts were toxic, causing over 75% A. fragariae mortality within 2-8 DAT. Toxicity of intact cadavers to A. fragariae increased with exposure time. We conclude that both curative and preventive applications of S. carpocapsae infected host cadavers can suppress A. fragariae populations on hosta. This suppressive effect can result from toxic metabolites produced by the nematodes or their symbiotic bacteria.