Change in acceptability of barley plants to aphids after exposure to allelochemicals from couch-grass (Elytrigia repens).
The response of the bird cherry-oat aphid, Rhopalosiphum padi, to barley plants was investigated following exposure of the plants to root allelochemicals from the aggressive weed couch-grass, Elytrigia (Agropyron) repens. Plants were treated either with root exudates from living couch-grass plants or with previously identified couch-grass root compounds 15-hydroxyindole-3-acetic acid, DL-5-hydroxytryptophan, L-5-hydroxytryptophan hydrate, and 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (carboline)] either separately or in mixtures. In choice and no-choice settling tests, aphid acceptance of barley plants was significantly reduced following treatment with root exudates, and the carboline when tested alone or in combination with the other compounds. In contrast, the other compounds without the carboline were less active in reducing aphid acceptance. In a probing bioassay, individual substances were either neutral or stimulatory to aphids, indicating that the reduced settling was probably not due to direct effects on aphids, but rather due to effects on the plant. This was confirmed in olfactometer assays, in which aphids were repelled by odors from barley plants following treatment with a mixture containing all four chemicals.
Glinwood
Robert
R
Department of Entomology, Swedish University of Agricultural Sciences, P.O. Box 7044, S-750 07 Uppsala, Sweden. robert.glinwood@entom.slu.se
Pettersson
Jan
J
Ahmed
Elham
E
Ninkovic
Velemir
V
Birkett
Michael
M
Pickett
John
J
D000818:Animals; D001042:Aphids; D001681:Biological Assay; D005247:Feeding Behavior; D001467:Hordeum / Q000737:chemistry*; D010675:Pheromones / Q000494:pharmacology*; D018515:Plant Leaves; D006109:Poaceae / Q000737:chemistry*; D012903:Smell
D010675:Pheromones