Am. Koppenhofer et al., EFFECT OF NEMATODE-TRAPPING FUNGI ON AN ENTOMOPATHOGENIC NEMATODE ORIGINATING FROM THE SAME FIELD SITE IN CALIFORNIA, Journal of invertebrate pathology, 68(3), 1996, pp. 246-252
We determined whether nematode-trapping fungi may influence the dynami
cs of a coastal shrub community. The food chain interactions in the sh
rub community involve the dominant plant species, its major insect her
bivore, and an entomopathogenic nematode, Heterorhabditis hepialus. Of
the 12 nematode-trapping fungi previously isolated from soils at the
study site, 5 were selected for this study. Arthrobotrys oligospora, G
eniculifera paucispora, Monacrosporium eudermatum, and Monacrosporium
cionopagum efficiently trapped and colonized H. hepialus on agar; in c
ontrast Nematoctonus concurrens trapped but did not infect or colonize
the nematode on agar. To determine whether these fungi can suppress H
. hepialus in soil, we added the fungi in the form of fungal-colonized
nematodes to pasteurized (2 hr at 62 degrees C) and raw (nontreated)
soil from the study site. Suppression was measured by comparing nemato
de invasion into a wax moth larva in fungus-treated and untreated soil
in vials at 20 degrees C. Fungal population density in soil was estim
ated using dilution plating and most probable number procedures. All f
ungi suppressed H. hepialus if the wax moth larvae were added 4 days a
fter the nematodes. Suppression ranged between 37 and 54% and did not
differ among fungi. Suppression was usually greater in raw than in pas
teurized soil. Raw soil contained a constant background of nematode-tr
apping fungi, and A. oligospora was the most common among these; no ba
ckground was detected in pasteurized soil. The presence of background
fungi in raw soil may explain the higher suppression in raw than in pa
steurized soil. Fungal propagule densities in our laboratory experimen
ts were similar to those observed in the field, suggesting that nemato
de-trapping fungi may influence the dynamics of the plant, insect herb
ivore, and entomopathogenic nematode in the coastal ecosystem. (C) 199
6 Academic Press, Inc.