The role of root architecture in foraging behavior of entomopathogenic nematodes

Authors: DEMARTA, LANILA - University Of Missouri; Hibbard, Bruce; BOHN, MARTIN - University Of Illinois; HILTPOLD, IVAN - University Of Missouri

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2014
Publication Date: 10/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59605
Citation: Demarta, L., Hibbard, B.E., Bohn, M.O., Hiltpold, I. 2014. The role of root architecture in foraging behavior of entomopathogenic nematodes. Journal of Invertebrate Pathology. 122:32-39.

Interpretive Summary: Entomopathogenic nematodes (EPN) are parasitic nematodes that attack insects and important components of integrated pest management programs for several major pests. Unfortunately, EPN infectiousness varies substantially. A better understanding of host-finding behavior in the soil is crucial to enhance EPN potential in biological control. It was previously demonstrated that roots can be used as a pathway to insect hosts by EPN, but this interaction and its impact on EPN foraging remain poorly documented. Artificial model-roots with three different degrees of complexity and connectivity were designed to investigate the impact of root architecture on foraging behavior of a major EPN. EPN located hosts better in presence of simple artificial roots. Complex artificial roots decreased foraging performance compared to simple roots. Adding synthetic root volatiles (chemical attractants) dramatically changed this pattern and favored the EPN on the most complex model-roots. This study adds important basic information to the scarce body of literature characterizing physical interactions between EPN and roots. The present data illustrate that root architecture not only modifies plant quality but also shapes the ecology of upper trophic levels. Understanding host location by EPN may assist in application strategies to manage major pests.

Technical Abstract: 1. As obligate parasites, entomopathogenic nematodes (EPN) rely on insect hosts to complete their development. In insect pest management, EPN infectiousness has varied a lot. A better understanding of their host-finding behavior in the rhizosphere is therefore crucial to enhance EPN potential in biological control. Previously demonstrated, roots can be used as a pathway to insect hosts by EPN, but this interaction and its impact on EPN foraging remain poorly documented. 2. Artificial model-roots with three different degrees of complexity and connectivity were designed to investigate the impact of root architecture on foraging behavior of the EPN Heterorhabditis megidis. Insect baits were placed at the bottom of each root that was subsequently buried in moist sand. 36 hours after EPN injection, the number of EPN-infected baits as well as the number of mature nematodes inside each individual carcass was recorded. Influence of insect-induced root volatile was also evaluated by spiking the baits with synthetic versions of these natural root volatiles. The ecological relevance of the results was tested in soil with maize plants exhibiting varied root architectures. 3. EPN performed better in presence of model-roots. However, the model-root complexity rapidly reached a threshold after which H. megidis foraging performances decreased. Adding a synthetic root volatile dramatically changed this pattern and favored the EPN on the most complex model-roots. Not only moving along model-root systems, H. megidis also crawled along maize roots to find the insect baits in soil and natural root architecture shaped EPN foraging behavior. 4. This study adds to the scarce body of literature characterizing physical interactions between EPN and roots. The present data illustrate that root architecture not only modifies plant quality but also shapes upper trophic levels’ ecology. This raises miscellaneous hypotheses underlying a broader impact of roots on the rhizosphere.