Movement patterns in Entomopathogenic nematodes: Continuous vs. temporal

To exploit resources, animals implement various foraging behaviors to increase their fitness. Entomopathogenic nematodes are obligate parasites of insects in nature. In previous studies, entomopathogenic nematodes were reported to exhibit group movement behavior in the presence and absence of insect hosts. However, it was not determined if group movement is continuous or temporal. For example, nematode movement behavior upon emergence from the host might start out in an independent fashion prior to aggregation, or group movement may be exhibited continuously. In the present study, we explored the propensity for innate group movement behavior of two insect parasitic nematodes in two families and genera: Heterorhabditis indica and Steinernema carpocapsae. We hypothesized the nematode populations would initially move independently from their origin and then come together for group movement. Movement patterns were investigated in sand when nematodes were applied in aqueous suspension (via filter paper) to a specific locus or when the nematodes emerged naturally from infected insect hosts. To compare nematode movement behavior over time and space, nematode dispersal was monitored at three distances (2.5, 4.5 and 8.0 cm) from the center (origin) and at two different time periods, 2 days and 3 days after nematode addition. We discovered that nematode dispersal continuously exhibited an aggregative pattern (independent movement was not observed). Results from both nematode species as well as the host-cadaver and filter paper (aqueous nematode suspension) application methods indicated a continuous aggregative pattern. The discovery of continuous aggregative movement patterns in steinernematid and heterorhabditid nematodes elucidates further the complexity of their foraging behavior and may serve as basis for exploring foraging behavior in other host-parasite systems.