Response of ants to a deterrent factor(s) produced by the symbiotic bacteria of entomopathogenic nematodes

The production of an ant-deterrent factor(s) (ADF) by Xenorhabdus nematophila and Photorhabdus luminescens, the symbiotic bacteria of the nematodes Steinernema carpocapsae and Heterorhabditis bacteriophora, respectively, was examined. In addition to an in vivo assay in which bacteria were tested for their ability to produce ADF within insect cadavers (M.E. Baur, H. K. Kaya, and D. R. Strong, Biol. Control 12:231-236, 1998), an in vitro microtiter dish assay was developed to monitor ADF activity produced by bacteria grown in cultures. Using these methods, we show that ADF activity is present in the supernatants of bacterial cultures, is filterable, heat stable, and acid sensitive, and passes through a 10-kDa-pore-size membrane. Thus, ADF appears to be comprised of a small, extracellular, and possibly nonproteinaceous compound(s). The amount of ADF repellency detected depends on the ant species being tested, the sucrose concentration (in vitro assays), and the strain, form, and age of the ADF-producing bacteria. These findings demonstrate that the symbiotic bacteria of some species of entomopathogenic nematodes produce a compound(s) that deters scavengers such as ants and thus could protect nematodes from being eaten during reproduction within insect cadavers.