Movers and Shakers: Do nematodes that move more infect more?

Authors: Slusher, Eddie; LEWIS, EDWIN - University Of Idaho; STEVENS, GLEN - University Of Idaho; Shapiro Ilan, David

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2024
Publication Date: 1/31/2024
Citation: Slusher, E.K., Lewis, E., Stevens, G., Shapiro Ilan, D.I. 2024. Movers and Shakers: Do nematodes that move more infect more?. Biological Control. 203/108060. https://doi.org/10.1016/j.jip.2024.108060.
DOI: https://doi.org/10.1016/j.jip.2024.108060

Interpretive Summary: Entomopathogenic nematodes (a kind of small round worm) have been used as biological control agents of various insect pests. An understanding of their behavior is important in order make them better biological control agents. Previous research has shown that nematodes may use multiple foraging styles when looking for a host (cruising, ambushing, and intermediate), this occurs both between different species and also among the individuals of a species. Movement can be risky to a nematode as it increases the risk of predation or desiccation. Thus, we predict that there may be benefits to moving through the soil such as increased invasion of a host insect. We assessed rather EPNs that moved farther across a soil column were also more successful at invading a host compared to nematodes that didn't move from the point of origin. We found that mover EPNs that are typically cruisers or intermediate foragers (Steinernema riobrave, Heterorhabditis bacteriophora, and H. indica) were more successful invaders. S. carpocapsae (an ambusher nematode) was the only species assessed that didn't gain any benefits from movement. This supports our hypothesis that EPNs may gain some benefits from moving through the soil to find a host. The results of this study can be used to develop strains that are better invaders by developing strains that are more efficient movers.

Technical Abstract: Entomopathogenic nematodes (EPNs) are roundworms that parasitize insects with the aid of symbiotic bacteria. These nematodes have been used both as model organisms and for biological control of pests. The specialized third stage of an EPN, known as an infective juvenile (IJ) must forage to find a host (cruising, ambushing, and intermediate) with strategies varying from species to species. Some IJs move more than others to find a host, despite risk of predation and desiccation. This hints at potential underlying benefits (e.g.,, invasion) for EPNs that move more. We assessed whether EPNs that moved farther across a soil column also exhibit higher levels of infectivity (invasion rates) when compared to nematodes that remained at or near their point of origin. We found that movers in the cruisier and intermediate species: Steinernema riobrave, Heterorhabditis bacteriophora, and H. indica had increased invasion rates compared to their counterparts that did not move. S. carpocapsae, an ambusher, did not exhibit infectivity differences between EPNs that moved versus those that did not. For the three cruiser/intermediate EPNs we tested, our results support our hypothesis that EPNs that tend to move more possess other benefits such as infectivity. Further studies are required to explore other parameters that may interact with movement. The results of this study can potentially be used to develop EPN strains that move more and infect more, and thus can potentially be more effective biological control agents.