Effect of cucurbitacin D on in vitro growth of Xenorhabdus and Photorhabdus spp., symbiotic bacteria of entomopathogenic nematodes

In vitro assays were conducted to determine the effect of cucurbitacin D, an oxygenated tetracyclic triterpenoid found in cucurbits, on the growth of Xenorhabdus isolated from Steinernema carpocapsae (All, Mexican, Agriotos strains), Steinernema riobravis, Steinernema glaseri (NC strain, strain 27), and Photorhabdus from Heterorhabditis bacteriophora (NC, Lewiston strains), and Heterorhabditis sp. (FL2122 strain). Cucurbitacin D inhibited the growth of four isolates, had no effect on the growth of four isolates, and stimulated the growth of one isolate. Results are discussed in relation to progeny production of entomopathogenic nematodes from insects that have eaten plant material containing cucurbitacin D. This is the first report of an effect of a plant secondary compound on the bacterial symbionts of entomopathogenic nematodeS.