Factors Affecting Rate of Honeydew Deposition by Therioaphis maculata (Buck.) and Toxoptera graminum (Rond.)1

Abstract

Various factors affecting the rate of honeydew deposition by the greenbug ( Toxoptera graminum (Rond.)) and the spotted alfalfa aphid ( Therioaphis maculate (Buck.)) were studied and the reactions of the two species compared. A method was developed whereby honeydew droplets from one aphid feeding for a '24-hour period on a plant part were caught on the bottom or sides of plastic cages. The rate of honeydew deposition was affected significantly in both the greenbug and the spotted alfalfa aphid by: (1) changes in temperatures; (2) different plant parts as feeding sites (leaf, stem, petiole); (8) different varieties of plants; and (4) the amount of light reaching the host plant and feeding site. The following factors were found to affect significantly the rate of honeydew deposition by the greenbug: (1) the area of feeding on a Reno barley leaf; (2) feeding on leaves yellowed by age; (8) reduced moisture to host plant. Changes in the following factors or conditions did not affect significantly the rate of honeydew deposition by the spotted alfalfa aphid: (1) reduced moisture to host plant or (!t) distance of leaves from growing point. The rate of honeydew deposition on Reno and Dicktoo barley and Pawnee wheat exceeded that found on the alfalfa varieties studied. This implies that the problems resulting from honeydew might be as great on barley and wheat as on alfalfa if it were not for the different methods in cultivation and harvesting time. The rate of honeydew deposition was found to be influenced almost directly in proportion to the known amount of resistance found in the host plants used. This condition suggests the possibility that the rate of honeydew deposition by aphids may be used to measure the degree of resistance of host plants to aphids, the rate of ingestion of plant material, and to serve as a crude measure of the metabolic activity of the insect.