Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2001
Publication Date: 2/1/2002
Citation: BURD, J.D. PHYSIOLOGICAL MODIFICATION OF THE HOST FEEDING SITE BY CEREAL APHIDS (HOMOPTERA: APHIDIDAE). JOURNAL OF ECONOMIC ENTOMOLOGY. 2002. V. 95. P. 463-468.
Interpretive Summary: The greenbug is an important pest of wheat in the United States. Economic infestations occur annually and are primarily controlled by insecticides. Reliance on chemicals to control insect pests has led to environmental concerns which have stimulated research focusing on alternate methods of insect control. One alternative approach to greenbug management has been the development and use of resistant crops. However, the occurrence of new greenbug biotypes has been a major obstacle to the deployment of resistant wheat cultivars. Therefore, it is important that a fundamental understanding of the mechanisms of greenbug damage be established to facilitate new approaches for developing plant resistant. The objectives of this study were to determine the effects of greenbug feeding on plant vascular tissue and to evaluate the movement and accumulation within the plant of greenbug-injected salivary compounds. In addition, the effect of feeding by Russian wheat aphids was compared with responses induced by greenbugs. It was found that greenbugs, by modifying the plant's transport system, significantly reduced the movement of plant nutrients from their feeding site, thereby making it more nutritious for a protracted period of time. This response occurred independent of the typical visible damage caused by greenbug feeding and implies that there is a second site of action that could potentially be used by plant breeders to enhance plant resistance. Greenbugs were also found to inject salivary compounds into leaf tissue that were transported to other locations within the plant. The accumulation of these compounds in the plant roots may account for the significant reductions in root biomass that accompany greenbug infestations.
Technical Abstract: IAA-1-14C and 14C-sucrose labels were used to study the effects of greenbugs, Schizaphis graminum (Rondani), and Russian wheat aphids, Diuraphis noxia (Mordvilko), on phloem function of wheat (Triticum aestivum L.). Greenbug feeding significantly reduced translocation from the immediate feeding site; however, phloem integrity was not impeded. In contrast, Russian wheat aphids had little effect on vein loading or phloem translocation at the feeding site. Results suggested that the inhibition of translocation caused by greenbugs might be due to a general inactivation of membrane-bound electrogenic proton pumps. Similar results were obtained when resistant and susceptible wheats were infested with three different greenbug biotypes, suggesting that this physiological response occurs independent of visible damage symptoms. Greenbugs fed artificial diets containing 14C-sucrose injected salivary material that was translocated to both root and shoot systems. The accumulation of salivary constituents in the roots of wheat seedlings may account for the significant reductions in root biomass that have previously been reported.