Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2008
Publication Date: 8/16/2008
Citation: Olson, D.M., Davis, R.F., Wackers, F.L., Rains, G.C., Potter, T.L. 2008. Plant-herbivore-carnivore interactions in cotton, Gossypium hirsutum: Linking belowground and aboveground. Journal of Chemical Ecology. 34:1341-1348. DOI:10.1007/s10886-008-9532-1. Interpretive Summary: Most studies on plant-herbivore interactions focus on either root or shoot feeding in isolation, but above- and belowground feeding may interact on a shared host plant. Cotton plants produce a variety of chemicals (e.g. terpenoid aldehydes) that exhibit toxicity to a wide range of plant feeders. Cotton plants also can emit volatile compounds after leaf and fruit-feeding, and as these volatile compounds attract natural enemy species of the plant feeder, they are thought to represent a type of plant defense. Our study evaluated terpenoid production by cotton plants in response to leaf feeding by an insect larvae, and root feeding by a plant parasitic nematode or their combination, as well as the attraction of a predator of the insect larvae to those plants. After 48 hours of leaf feeding and 5 weeks of root feeding, increased volatile terpenoids occurred with leaf-feeding regardless of root feeding. In addition, the predator was attracted only to plants with leaf feeding. In contrast to previous studies in cotton, terpenoid aldehydes were not induced in leaf and root tissue following foliage or root herbivory, or their combination. We conclude that root feeding by a nematode species has little influence on defenses of cotton plants against an insect leaf-feeder.
Technical Abstract: We subjected cotton plants to 48 hours of leaf feeding by an insect larvae and 5 weeks of root feeding by a plant parasitic nematode to determine if typical plant tissue defenses and plant chemical volatiles (commonly attractive to predators of the insect larvae) are affected by the presence of both herbivores. The insect larvae were caged on 3 leaves per plant to standardize damage. The nematodes were inoculated into the soil at a rate of 20,000 eggs/pot. Plant tissues were freeze dried, ground and examined for tissue defense compounds using HPLC. Gas chromatography/Mass spectrometry was used to analyze the volatile compounds collected from each plant. A wasp predator of the insect larvae was used in a wind tunnel study to determine if the plants fed upon by both leaf and root feeders are attractive. We found no evidence of increased levels of plant defense compounds in leaf and root tissue following leaf or root feeding, or their combination. The plants only produced volatile compounds and were attractive to the predator when there was leaf feeding. We conclude that root feeding by a nematode species has little influence on defenses of cotton against an insect leaf-feeder.