THE INFLUENCE OF PHOTORHABDUS-LUMINESCENS STRAINS AND FORM VARIANTS ON THE REPRODUCTION AND BACTERIAL RETENTION OF HETERORHABDITIS-MEGIDIS

The preference of nematodes for feeding on, and retention of strains a nd form variants of symbionts was tested. Heterorhabditis megidis stra ins DH-SH1 (= HSH) and NLH-E87.3 (= HE) could multiply on the primary forms of both symbionts, Photorhabdus luminescens strains PSH/1 and PE /1, respectively, and did not prefer one strain to the other. Both nem atodes could not reproduce on the secondary form of their own symbiont ; however, HSH could multiply on the secondary form PE/2. This suggest s that the negative effect a secondary form bacterium has on nematode reproduction, is not a common factor in all secondary forms. When put on a plate with primary and secondary form bacteria, most infective ju veniles preferred to feed on primary form bacteria. All nematodes were able to retain the bacteria they bad been cultured on, including the secondary form. These results suggest that the nematodes prefer the pr imary form as a food source but the retention of bacteria is not as sp ecific as suggested before in the literature.