Submitted to: Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/2/2006
Publication Date: 1/4/2007
Citation: Christen, J.M., Campbell, J.F., Lewis, E.E., Shapiro Ilan, D.I., Ramaswamy, S.B. 2007. Responses of the entomopathogenic nematode, Steinernema riobrave, to its insect hosts, Galleria mellonella and Tenebrio molitor. Parasitology 134:889-898. Interpretive Summary: Nematodes that attack insects and their associated bacteria are biological control agents for many species of insect pests, but their effectiveness when applied in large numbers for insect control may be limited due to their preference for already infected hosts. The process of host selection and the nature and source of the cues used are not well understood. In this study, we investigated responses of one species of nematode to two species of insects that were previously parasitized by both nematodes and bacteria or by bacteria alone to determine if and when preference occurs, and the role bacteria plays in the production of cues used in making infection decisions. Infection was found to decline the longer the insect had been parasitized, but nematodes preferred insects parasitized for 24 hours when given a choice between two insects that had been parasitized from 0 to 72 hours. This research provides a foundation from which to investigate the influence of these host changes on nematode behavior. Ultimately, these cues may be used to manipulate nematode behavior to enhance their ability to control insect pest populations.
Technical Abstract: Potential hosts for infective juveniles of entomopathogenic nematodes can vary considerably in quality based on the characteristics of the host species/stage, physiological status (e.g., stress, feeding on toxins), and infection status (heterospecific or conspecific infection). Host acceptance may also be influenced by the status of the nematode (sex, infectivity, and age). In this study, we investigated responses of the entomopathogenic nematode Steinernema riobrave to hosts (Galleria mellonella or Tenebrio molitor) that were previously parasitized with conspecifics or injected with the nematode-symbiotic bacterium, Xenorhabdus sp., to determine if there is a preference for previously parasitized/injected hosts and when this preference might occur. In no-choice bioassays, the number of juveniles infecting both host species decreased linearly with increasing time post-infection. However, infective juveniles continued to infect previously parasitized hosts up to 72 h. Significant preference was exhibited by S. riobrave for 24 h post-infection G. mellonella larvae over uninfected and 24 h post-injection G. mellonella larvae over 48 h post-injection larvae. No significant preference was exhibited by S. riobrave for T. molitor hosts previously parasitized with conspecifics or those injected with bacteria in any treatment combination. Such preference for, or continued infection of parasitized insects, has the potential to impact nematode efficacy.