Do biotype-1 soybean aphids benefit from the presence of biotype-2 on resistant soybean?

Despite the genetic bottleneck that Aphis glycines passed through on the way to North America and the sparse use of aphid-resistant soybeans (i.e. Rag genes) in North America, biotypes have been identified that overcome this resistance. Plant defenses may be up regulated based on the density of herbivores attacking the plant. However, large populations of insects can overcome plant basal defenses thereby inducing susceptibility. Induced plant susceptibility allows for avirulent populations of insects to feed on resistant plants. Our objective was to determine if a population of virulent biotype (biotype-2) A. glycines could facilitate the growth of an avirulent (biotype-1) population on soybean containing the Rag1 gene. We compared the impact of an initial population of biotype-1 and biotype-2 A. glycines on a subsequent population of both biotype-1 and biotype-2. The initial population varied by two densities (0 or 50 aphids) and were caged on the first trifoliate of a V2 soybean plant. After 24-hours, a secondary population of aphids was placed on the second trifoliate, and the growth rate of this secondary population was measured over 10 days. Results indicate that populations of biotype-2 A. glycines facilitate the growth of biotype-1 on Rag1soybean significantly. Indicating that co-occurring biotype-1 and biotype-2 populations of soybean aphids on resistant soybean will be indistinguishable.