Movers and shakers: Do nematodes that move more invade more?

(a) ∼20,000 ijs of four different commercial species of entomopathogenic nematodes were individually placed in vertically oriented PVC columns containing oven-dried sand. (b) Ijs were incubated for varying time periods depending on species as species move at different rates. (c) After incubation time, the top section (containing non-moving nematodes) and the bottom section (containing moving nematodes) of each PVC column was removed and rinsed in water to decant ijs from sand. (d) 500 ijs were sampled from the non-mover and mover ijs in each column. These ijs were exposed to a Galleria mellonella larva and allowed to infect the larva. After 24 hours, the larva was dissected and the number of ijs inside the insect was counted. (e) The percent invasion was compared between movers and non-movers using JMP® Pro 14.1.0 to determine if nematodes that move more have a higher infectivity rate than non-movers. [Display omitted] • Increased dispersal of EPNs may provide tradeoffs, such as risk of mortality in exchange for increased invasion potential. • Invasion of G. mellonella was assessed between the "movers" and "non-movers" of four species of entomopathogenic nematode. • S. carpocapsae movers were the only nematodes that did not show increased invasion potential. • H. indica , traditionally classified as a cruiser forager, had a movement index similar to an ambush forager. • EPNs classified as ambushers may not gain increased invasion success compared to EPNs who are cruisers or intermediates. 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 with strategies varying from species to species (cruising, ambushing, and intermediate). Some IJs move more than others to find a host, despite an increased risk of predation and desiccation. This hints at potential underlying benefits (e.g., increased invasion) for EPNs that move more. We assessed whether EPNs that moved farther down a soil column also exhibit higher levels of invasion 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 higher invasion rates compared to their counterparts that did not move. S. carpocapsae , an ambusher, did not exhibit invasion 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 enjoy related benefits such as increased invasion potential. 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 invade more, and thus can potentially be more effective biological control agents. [ABSTRACT FROM AUTHOR]