Effect of mulches on persistence of entomopathogenic nematodes (Steinernema spp.) and infection of Strobilomyia neanthracina (Diptera : Anthomyiidae)in field trials

The effect of mulches on the persistence of entomopathogenic nematodes, Ste inernema spp., for infecting larvae of the spruce cone maggot, Strobilomyia neanthracina Michelsen, was tested in a series of field trials conducted i n New Brunswick, Canada Feat mulch increased the percentage of maggots infe cted with Steinernema feltiae strain 27 (=bibionis) (Filipjev) strain 27, S . feltiae Umea and Steinernema carpocapsae (Weiser) All strain, when maggot s were placed on nematode-treated soil beneath the pest layer. However, whe n maggots were placed on the surface of the peat (to simulate larvae droppi ng) in a subsequent experiment, the percentage of maggots infected by S. fe ltiae strain 27 was less than half of that for maggots placed beneath the p eat. Significantly fewer maggots were infected in peat than in either sand or petting soil in a laboratory experiment Mean percentage of maggots infec ted by S, feltiae strain 27 over a 21-d period after application was not in creased by retaining a natural vegetative cover, or by mulching with hay, w ood-bark chips, or bark. Bark mulch, however, did reduce the rate of declin e in percentage of infection over time. The numbers of S, feltiae infective juveniles present in the soil from 0 to 3 wk after application were estima ted in 2 field trials by repeated baiting with greater wax moth larvae. Num bers of infective juveniles per gram of soil were positively related to per centage of cone maggots infected in 1 of 2 yr,but were not significantly af fected by mulching. Mulching with hay, bark, or wood-bark resulted in signi ficantly lower soil moisture potentials compared with nonmulched treatments . The results suggest that the mulches tested in this study would not maint ain adequate efficacy or persistence of S. feltiae strain 27 for suppressio n of cone maggot over the 2- to 4-wk period of larval drop.