Entomopathogenic nematodes and their symbiotic bacteria are lethal endoparasites of insects. Although much is known about how infective juveniles (IJs) search for hosts, less is known about the infection process. Infective juveniles may encounter insects already parasitized and this can influence whether or not they infect. Using Steinernema riobrave and two host insect species, Galleria mellonella (L.) and Tenebrio molitor (L.), the influence of host parasitization status on infection by IJs was determined using choice bioassays. S. riobrave showed significant preference for 24 h infected over uninfected G. mellonella larvae and 48 h infected over 24 h infected T. molitor larvae. Previous studies indicated that infected T. molitor had lower levels of CO₂ production and delayed nematode development to adulthood compared to G. mellonella. Because bacteria growing in the host hemocoel may be a source of cues used by IJs during infection, Xenorhabdus sp. population growth curves were determined for both hosts using whole insect homogenates plated onto NBTA. There was a dramatic increase in the number of Xenorhabdus sp. CFUs starting at 24 h in G. mellonella and 48 h in T. molitor. Our findings suggest that IJ infection behavior is correlated with changes in bacterial levels within an infected host. Experiments assessing IJ infection of hosts injected with Xenorhabdus sp., but without nematodes will be conducted to further evaluate this potential bacterial role in entomopathogenic nematode infection behavior.