Location: Chemistry ResearchTitle: Sending mixed messages: a trophic cascade produced by a belowground herbivore-induced cue) Author
Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2013
Publication Date: 8/31/2013
Citation: Ali, J.G., Campos-Herrera, R., Alborn, H.T., Duncan, L.W., Stelinski, L.L. 2013. Sending mixed messages: a trophic cascade produced by a belowground herbivore-induced cue. Journal of Chemical Ecology. 39:1140-1147. Interpretive Summary: Scientists at USDA ARS Gainesville FL have previously, together with colleges at University of Florida and Rutgers University shown that roots of citrus defend themselves against herbivores by releasing an herbivore induced plant volatile (HIPV) named pregeijerene (1,5-dimethylcyclodeca-1,5,7-triene) and that this HIPV attracts naturally occurring entomopathogenic nematodes (EPNs) to insect larvae when applied in the field. In a continued collaboration the scientists here provide further evidence that subterranean HIPVs might function much the same as HIPV aboveground by attracting not only parasitoids, but also hyperparasites and other food web members. Molecular probes were designed to detect and quantify free-living bacterivorous nematodes from the Acrobeloides–group (FLBNs), some of which compete with EPNs by ‘hyperparasitizing’ insect cadavers, and in addition 5 species of nematophagous fungi (NF), known to infect and kill EPNs. Of the diverse species of nematodes and fungi found in two agricultural systems (citrus and blueberry), only FLBNs were found to be attracted to pregeijerene, thus behaving similar to EPNs. Although detected in the soil at both locations, NF abundance was not significantly affected by the presence of the belowground HIPV. It still remain to be investigated if root or nematode related signals affect NF in any other way, for example their infectability of nematodes.
Technical Abstract: Plants defend themselves against herbivores both directly (chemical toxins and physical barriers) and indirectly (attracting natural enemies of their herbivores). Previous work has shown that roots of citrus defend themselves against root herbivores by releasing an herbivore induced plant volatile (HIPV), pregeijerene (1,5-dimethylcyclodeca-1,5,7-triene), that attracts naturally occurring entomopathogenic nematodes (EPNs) to larvae when applied in the field. However, the soil community is complex and contains a diversity of interspecies relationships that modulate food web assemblages. Herein, we tested the hypothesis that other nematode types beyond EPNs, as well as, nematophagous fungi are affected by the same HIPV that attracts EPNs to herbivore-damaged roots. We employed molecular probes designed to detect and quantify nematodes from the Acrobeloides–group (a type of free-living bacterivorous nematode (FLBNs) species), some of which compete with EPNs by ‘hyperparasitizing’ insect cadavers, and 5 species of nematophagous fungi (NF), which attack and kill EPNs. In two different agricultural systems (citrus and blueberry), we detected diverse species of nematodes and fungi; however, only the behavior of FLBNs was affected in a manner similar to that reported previously for EPNs. Although detected, NF abundance was not affected by the presence of the belowground HIPV. We provide the first evidence showing subterranean HIPVs function much the same as those aboveground, attracting not only parasitoids, but also hyperparasites and other food web members.