Parasite infective stages evaluate a potential host for its suitability before committing to infection. A host has traditionally been regarded as a static entity, but more than one individual often infects a single host. As the infection in a host progresses, the value of the host as a resource to an infective stage parasite changes. Thus, host-parasite interactions are dynamic and infective stages are predicted to respond differently to hosts at different points in the infection process. The objective of this research is to explain behavioral interactions between insect-parasitic nematodes and their hosts. Specifically, how parasite infective stage behavior (host attraction and penetration) is affected by changes in volatile host cues and contact host cues during the course of infection will be addressed. Then, the fitness consequences of decisions based upon these cues by the parasites will be determined. Ultimately, how parasites decide whether or not to infect a host, and how the costs and benefits of decisions influence parasite success, will be explained. The impact of this research includes: 1) improved understanding of parasite/host relationships, 2) increased predictability of insect-parasitic nematodes as biological control agents for insects, 3) increased opportunities for undergraduate students of underrepresented groups to conduct research, 4) development of insect-parasitic nematode/host association as a teaching tool for advanced undergraduate courses.