Comparison of Foliar and Soil-Drench Applications of Aqueous Rubidium Chloride Solutions to Plants for Marking Feeding Aphids (Homoptera: Aphidae)

Abstract

Aqueous solutions of rubidium chloride, RbCl, (10 g/1, 10,000 ppm) were applied to foliage or soil of potted bell pepper and tomato. After 48 h, green peach aphid (Myzus persicae Sulzer) and potato aphid (Macrosiphum euphorbiae Thomas) were transferred to pepper and tomato, respectively. Leaf and aphid samples were collected after 6 d; remaining aphids were transferred to untreated plants. Aphid samples were collected periodically for 5 to 7 d. All samples were analyzed for Rb content. Results were similar for the pepper and tomato experiments. Soil-drench treatment produced significantly greater levels of Rb in leaf and initial aphid samples relative to foliar treatment. Levels of Rb in aphids from the two treatments were comparable after aphids fed on untreated plants for 24 h. Levels of Rb in aphids declined rapidly after removal from the source: undetectable by Day 6 in the potato experiment and reduced by nearly 90% by Day 5 in the tomato experiment. Foliar application of RbCl solution should be used in field situations. Application is more precise, and the length of detection is comparable with soil drench. Additionally, soil drenching with Rb produced an initially high peak of Rb in the aphids, which may have a physiological effect.