PARENT SESSION
Wednesday, August 9, 8:00-11:30 am
COS 56 - Soil ecology
Mississippi, Mezzanine Level, Cook Convention Center
Presiders: S Baer and J Six

Linking infection decisions in entomopathogenic nematodes to life history characteristics.

Stevens, Glen^*,1, Arimoto, Hanayo¹, Lewis, Ed¹, ¹ University of California, Davis, Davis, CA

ABSTRACT- Entomopathogenic nematodes (EPNs) are soil dwelling, obligate insect parasites, and are important components of many soil food webs. All but one EPN life stage exists inside the host; the infect stage juvenile (IJ) is the only free-living stage, and exists solely to find and infect a new host. Once an IJ enters a host, development resumes. The decision to infect is irreversible, and host suitability and quality will influence not only its survival but also the environment experienced by subsequent generations. We have a limited understanding of how varying qualities of the host influence infection decisions in these nematodes, a factor that limits their effectiveness as biological control agents. The severe consequences associated with infection decisions suggest that IJ EPNs should have well-developed mechanisms for assessing host quality, and they may be excellent model organisms for assessing host choice behavior in parasites. We designed experiments to examine infection decisions made by three EPN species from the genus Steinernema: S. glaseri, S. feltiae, and S. carpocapsae. These species differ in terms of their foraging behaviors, host species range, and spatial distribution in soils. As infections result from invasion by multiple individuals, our goal was to examine how infection status influenced infection decisions in these species, and to attempt to correlate infection decisions with other life history characteristics. First, infected hosts (Galleria mellonella larvae) were exposed to IJs over a time course to determine how infection status influenced the decision to invade; in this case, tendency to invade declined significantly in all three species as the infection progressed (P<0.05). When provided with a choice between infected and uninfected hosts, both S. glaseri and S. feltiae preferred joining infected insects (P<0.05), while S. carpocapsae exhibited no preference. Comparing decision making to life history suggests that species with a cruising foraging habit (e.g., S. glaseri) that are more patchily distributed in the soil exhibit a preference for joining (rather than initiating) infections, while ambushing species (e.g., S. caropcapsae) that are more homogeneously distributed are more willing to initiate infections.

Key words: soil ecology, parasitism, entomopathogenic nematode