Submitted to: Journal of Chemical Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/17/2010
Publication Date: 3/23/2010
Citation: Ali, J.G., Alborn, H.T., Stelinski, L.L. 2010. Subterranean Herbivore-induced Volatiles Released by Citrus Roots upon Feeding by Diaprepes abbreviatus Recruit Entomopathogenic Nematodes. Journal of Chemical Ecology. 36: 361-368. Interpretive Summary: It is well known that herbivore induced volatile emissions benefit plants by recruiting natural enemies of herbivorous insects and such tritrophic interactions have been thoroughly examined in the above-ground terrestrial environment. In this paper a scientist at USDA ARS CMAVE, Gainesville, FL in collaboration with scientists at the University of Florida, Department of Entomology and Nematology show that similar tritrophic interactions also occur below ground. The larvae of the root weevil (Diaprepes abbreviatus) are a serious pest of citrus. Entomopathogenic nematodes have by varying, and unpredictable, success been used to control the weevil but interactions between the plant, insect and nematode have been poorly understood. In a root zone bioassay, root weevil infested root stock (Swingle citrumelo) recruited significantly more entomopathogenic nematodes (Steinernema diaprepesi) than non-infested or mechanically damaged roots, or larvae alone. By dynamic in situ collection and GC-MS analysis of volatiles from soil, in combination with a two choice sand-column bioassay it was found that Swingle citrus roots release induced volatiles in response to herbivore feeding and that some of these induced volatiles function as attractants for entomopathogenic nematodes. This work has highlighted the fundamental role of the host plant in below ground tritrophic interactions and work will give us new tools to select, or develop, citrus root stock with a high ability to recruit beneficial nematodes in response to a root weevil infestation.
Technical Abstract: Herbivore induced volatile emissions benefit plant hosts by recruiting natural enemies of herbivorous insects. Such tritrophic interactions have been thoroughly examined in the above-ground terrestrial environment. Recently, similar signals have also been described in the subterranean environment, which may be of equal importance for indirect plant defense. The larvae of the root weevil (Diaprepes abbreviatus) are a serious pest of citrus. Infestations can be controlled by the use of entomopathogenic nematodes, yet the interactions between the plant, insect and nematode are poorly understood and remain unpredictable. In bioassays using a root zone six-arm olfactometer, citrus roots (‘Swingle citrumelo’ rootstock) recruited significantly more entomopathogenic nematodes (Steinernema diaprepesi) when infested with root weevil larvae than non-infested roots. Infested plants were more attractive to nematodes than larvae alone. Roots damaged by weevil larvae attracted more nematodes than mechanically damaged roots and sand controls. By dynamic in situ collection and GC-MS analysis of volatiles from soil, we determined that four major terpene compounds were produced by infested plant roots that were not found in samples from non-infested roots or soil containing only larvae. Solvent extracts of weevil infested roots attracted more nematodes than extracts of non-infested roots in a two choice sand-column bioassay. These findings suggest that Swingle citrus roots release induced volatiles as an indirect defense in response to herbivore feeding and some of these induced volatiles function as attractants for entomopathogenic nematodes.