Submitted to: Journal of Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/20/2010
Publication Date: 12/22/2010
Citation: Ali, J.G., Alborn, H.T., Stelinski, L.L. 2010. Constitutive and induced subterranean plant volatiles attract both entomopathogenic and plant parasitic nematodes. Journal of Ecology. 99(1):26-35. Interpretive Summary: Although signals that mediate aboveground multitrophic interactions and indirect plant defenses are well documented, equally important interactions below ground are much less understood. A scientist at the chemistry group at USDA ARS, Center for Medical, Veterinary and Agricultural Entomology, Gainesville FL, in collaboration with scientists at the department of Entomology and Nematology, University of Florida, Lake Alfred, FL, have previously shown that when larvae of the root weevil, Diaprepes abbreviatus feed on hybrid Swingle citrus root stock, the roots are induced to release volatile compounds that attract the entomopathogenic nematode Steinernema diaprepesi. In this paper the same scientists showed that the same recruitment signals also are released by non-hybrid sour orange root stock when damaged by weevil larvae. They also show that these signals attract nematode species representing various foraging strategies (cruisers vs. ambushers) as well as trophic levels (plant parasites vs. entomopathogens). Interestingly, one of the swingle parent lines turned out to attract all the tested nematode species irrespective of insect herbivory and dynamic in situ collection and GC-MS analysis of volatiles from soil revealed that the parent lin released the recruitment signals constitutively regardless of weevil feeding. Volatile collections from above and belowground portions of citrus plants revealed that aboveground feeding by weevils did not induce belowground release of recruitment signals nor did damage by larvae belowground induce similar signals aboveground. In conclusion, the release of nematode attractants by citrus roots might occur broadly but for different plant species or cultivars this release can be constitutively or herbivore-induced which highlight the importance of utilizing root stocks with herbivore-induced responses for successful nematode based biological control.
Technical Abstract: Indirect plant defenses are well documented for the aboveground constituents of plants. Although less thoroughly investigated to date, belowground signals that mediate multitrophic interactions are equally important. Entomopathogenic nematodes (Steinernema diaprepesi) are attracted to herbivore-induced volatiles released from Swingle var. (Citrus paradisi x Poncirus trifoliata) citrus when fed upon by the root weevil, Diaprepes abbreviatus. Herein, we examined the extent to which belowground recruitment signals modify behavior of nematode species representing various foraging strategies (cruisers vs. ambushers), and trophic levels (plant parasites vs. entomopathogens). We compared attraction to volatile collections of weevil-infested roots 20 and non-infested roots from Swingle citrus rootstock and a parent line of the Swingle hybrid, Poncirus trifoliata (Pt). Swingle roots infested by weevils attracted more nematodes than non-infested roots irrespective of nematode foraging strategy and trophic status. The parental line of the swingle rootstock, Pt, attracted all nematode species irrespective of insect herbivory. Dynamic in situ collection and GC-MS analysis of volatiles from soil revealed that Pt roots release recruitment signals constitutively regardless of weevil feeding. A different non-hybrid citrus species (Sour orange, Citrus aurantium) released herbivore-induced nematode recruitment signals only in response to larval feeding. Volatile collections from above- and belowground portions of citrus plants revealed that aboveground feeding by 30 weevils does not induce production of nematode recruitment signals analogous to that induced by root damage nor does damage by larvae belowground induce a similar signal aboveground.