Ants were the most apparent invertebrate scavengers observed foraging
on entomopathogenic nematode-killed insects (i.e., insect cadavers con
taining entomopathogenic nematodes and their symbiotic bacteria) in th
e present study. Workers of the Argentina ant, Linepithema humile (May
r), scavenged nematode-killed insects on the surface and those buried
2 cm below the soil surface. Ant workers scavenged significantly more
steinernematid-killed (60-85%) than heterorhabditid-killed (10-20%) in
sects. More 4-day-postinfected cadavers (hosts died within 48 h after
exposure to nematodes) were scavenged than 10-day-postinfected cadaver
s. Ten-day-postinfected hosts contained live infective juvenile nemato
des therefore ants may serve as phoretic agents. Other ant species, in
cluding Veromessor andrei (Mayr), Pheidole vistana Forel, Formica paci
fica Francoeur, and Monomoriom ergatogyna Wheeler, also scavenged nema
tode-killed insects. These ant species removed or destroyed about 45%
of the steinernematid-killed insects. These results suggest that survi
val of steinernematid nematodes may be more significantly impacted by
invertebrate scavengers, especially ants, than that of heterorhabditid
nematodes, and placement of steinernematid-killed insects in the fiel
d for biological control may be an ineffective release strategy. Becau
se entomopathogenic nematodes kill insects with the help of symbiotic
bacteria, we tested the role of these bacterial species in deterring i
nvertebrate scavengers by injecting bacteria (without nematodes) into
insects and placing the cadavers in the field. None of the insects kil
led by the symbiotic bacterium, Photorhabdus luminescens (Thomas and P
oinar) from Heterorhabditis bacteriophora Poinar, were scavanged, wher
eas 70% of the insects killed by the symbiotic bacterium, Xenorhabdus
nematophilus (Poinar and Thomas) from Steinernema carpocapsae (Weiser)
, and 90% of the insects killed by Bacillus thuringiensis Berliner wer
e scavenged by the Argentine ant. We conclude that P. luminescens is r
esponsible for preventing ants from foraging on heterorhabditid-killed
hosts. (C) 1998 Academic Press.