Abstract
Photorhabdus luminescens is a gram-negative luminescent enterobacterium that symbiotically resides in the digestive tract of an entomopathogenic nematode (EPN) of the family Heterorhabditidae. Heterorhabditis bacteriophora upon entering an insect host, regurgitate P. luminescens cells, and the bacteria quickly establish a lethal septicemia. To expand the possibility of its cockroach control, the insecticidal activity of this nematode-bacterium complex against cockroaches was investigated in two ways. First, we examined the insecticidal activity of H. bacteriophora harboring P. luminescens against the middle-stage instar of three Periplaneta (P. fuliginosa, P. americana, and P. japonica) and one Blattella (B. germanica) cockroach species. Mortality of P. fuliginosa and P. americana were significantly increased when treated with 20,000 and 100,000 nematodes/0.3 g bait/ 5 cockroaches. The mortality of P. japonica, however, did not differ from that of the control at all of the tested concentrations; whereas, the mortality of B. germanica was relatively higher than that of Periplaneta cockroaches. Second, we tested the pathogenicity of P. luminescens alone against the three Periplaneta species by injection of bacterial cells. All tested cockroaches were found to be killed within 2–4 days. These results would suggest that Periplaneta are susceptible to P. luminescens; however, in the bait experiment, H. bacteriophora was unable to effectively establish a lethal infection of P. luminescens. Our results indicate that susceptibility to EPN infection and bacterial pathogenicity should be evaluated separately, and that much less H. bacteriophora is required to kill B. germanica than is needed to kill three Periplaneta cockroaches.
