FORAGING ANTS AS SCAVENGERS ON ENTOMOPATHOGENIC NEMATODE-KILLED INSECTS

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.