Differences in susceptibility of white grub species to entomopathogenic nematodes: the relative contribution of symbiotic bacteria and nematodes
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Series/Report no.:Entomology. Graduate student poster competition, 2007
As susceptibility of white grub species to entomopathogenic nematodes differs, we compared the virulence of Photorhabdus temperata and Xenorhabdus koppenhoferi, the symbionts of nematodes Heterorhabditis bacteriophora and Steinernema scarabaei, respectively, to three white grub species Popillia japonica, Rhizotrogus majalis, and Cyclocephala borealis. Both bacteria were virulent to all three grub species even at as low as 2 cells /grub. However, the median lethal dose at 48 h post injection and median lethal time at 20 cells /grub showed that P. temperata was more virulent than X. koppenhoferi to C. borealis. There were no differences in virulence of two bacteria against P. japonica and R. majalis. Although H. bacteriophora carrying P. temperata is less pathogenic than S. scarabaei carrying X. koppenhoferi to R. majalis, P. temperata grew faster than X. koppenhoferi both in vitro and in vivo. We then tested the pathogenicity of oral and hemolymph introduced H. bacteriophora to R. majalis to determine whether nematodes are able to successfully vector the bacteria into the hemolymph. Hemolymph injected H. bacteriophora were pathogenic to R. majalis indicating successful bacterial release, but orally introduced H. bacteriophora were not. Dissection of grubs confirmed that orally introduced H. bacteriophora were unable to penetrate into the hemolymph through the gut wall. Therefore, we conclude that the low susceptibility of R. majalis to H. bacteriophora is not due to the symbiotic bacteria, but is due to the nematode’s poor ability to penetrate through the gut wall to vector the bacteria into the hemolymph.
This research was supported by an interdisciplinary grant and a graduate research competitive grant from the Ohio Agricultural Research and Development Center, Wooster, Ohio.