Movement patterns in entomopathogenic nematodes: continuous vs. temporal

Authors: RUAN, WEIBIN - Nankai University; Shapiro Ilan, David; LEWIS, EDWIN - University Of Idaho; KAPLAN, FATMA - Non ARS Employee; Alborn, Hans; GU, X-H - Non ARS Employee; SCHLIEKELMAN, PAUL - University Of Georgia

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2017
Publication Date: 2/2/2018
Citation: Ruan, W., Shapiro Ilan, D.I., Lewis, E., Kaplan, F., Alborn, H.T., Gu, X., Schliekelman, P. 2018. Movement patterns in entomopathogenic nematodes: continuous vs. temporal. Journal of Invertebrate Pathology. 151:137-143. https://doi:10.1016/j.jip.2017.11.010.
DOI: https://doi.org/10.1016/j.jip.2017.11.010

Interpretive Summary: Entomopathogenic (insect-killing) nematodes are small round worms that are used as natural bio-insecticides. These nematodes only kill insects and are not harmful to human or the environment. In order to use beneficial nematode more effectively in biological pest suppression we need to understand their behavior. In a previous study, we discovered that nematode movement is not random but rather the nematodes move together in a group. One might liken their movement to group behavior in other animals such as a pack of wolves. However, it was not known whether the nematodes always move together in packs, or if they sometimes disperse individually (and only get together in group movement occasionally). In the present study, we discovered that the nematodes move continuously in aggregate (in groups). We hypothesize that the nematodes used aggregation pheromones to stay together. These findings contribute to the elucidation of nematode ecology, and may be leveraged to enhance biological control potential.

Technical Abstract: To exploit resources, animals implement various foraging behaviors to increase their fitness. 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. 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.