|FINER, JOHN - The Ohio State University|
|Redinbaugh, Margaret - Peg|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2015
Publication Date: 11/16/2015
Publication URL: https://handle.nal.usda.gov/10113/5695370
Citation: Todd, J.C., Mian, R.M., Backus, E.A., Finer, J.J., Redinbaugh, M.G. 2015. Feeding behavior of soybean aphid (Hemiptera: Aphididae) biotype 2 on soybean PI 243540, the source of Rag2 resistance. Journal of Economic Entomology. 109:426-433.
Interpretive Summary: The U.S. grows more than 75 million ares of soybeans each year with a market value of $36 billion. Soybean aphid continues to be the number one insect pest of soybeans in the U.S., costing growers more than $2 billion annually. Although several genes conferring resistance to soybean aphid have identified, little is known about how they work. In these experiments, we compared the behavior of one variant of soybean aphid, called biotype 2, on soybeans that carry a gene for resistance to the biotype with their behavior on a highly susceptible cultivar. Time-lapse photography showed that the aphids did not like stems of the resistant soybeans, but stayed to feed on the susceptible cultivar. We used a specialized apparatus, called an electrical penetration graph (EPG), to analyze the feeding behavior of the aphids on the resistant and susceptible soybeans. We found that the time it took for the aphids to probe the plant leaves was the same on both resistant and susceptible soybean, as were feeding behaviors that indicated the aphids were feeding on phloem sap. However, feeding behaviors that occurred between probing the leaf and finding the phloem were very much affected by feeding on resistant and susceptible soybean, with the behaviors indicating the aphids had trouble reaching their phloem feeding sites in resistant soybeans. The feeding behaviors indicated resistance was associated with cells in the soybean leaf epidermis and mesophyll. Our results will help scientists identify specific genes, chemicals and other factors in soybean that give it resistance to this important pest.
Technical Abstract: Host plant resistance to the soybean aphid, Aphis glycines Matsumura, is an effective means of controlling populations of this introduced pest species in the U.S. Rag (Resistance to Aphis glycines) genes identified in soybean germplasm have been incorporated into commercial cultivars, but differential responses by soybean aphid biotypes to the Rag genes have made understanding mechanisms associated with Rag genes increasingly important. We compared the behavior of biotype 2 aphids on soybean PI243540, which is the source of Rag2, and the highly susceptible cultivar Wyandot. Time-lapse animation indicated a strongly repellent effect of PI243540 on aphids. Scanning electron microscopy revealed that the abaxial surface of PI243540 leaves had a higher density of both long and glandular trichomes on veins. Electrical penetration graph (EPG) analysis showed that the time before aphids made their first probe did not differ between the resistant and susceptible soybean lines. Fewer aphids feeding on PI243540 reached the phloem, and the time before reaching the phloem was much longer relative to susceptible soybean. For aphids that reached the phloem, there was no difference in either in number of feedings or their duration in phloem. However, aphids feeding on resistant soybean had fewer prolonged phases of active salivation (E1) and many more pathway activities and non-probing intervals. Together, the feeding behavior of aphids suggested that Rag2 resistance was associated with properties of the epidermal and mesophyll tissues.