Genotypic diversity as a pest management tool: Effects of crop intraspecific diversity on soybean aphid and natural enemy populations

High plant diversity can improve the productivity and stability of ecosystems through complex ecological interactions. Presently, crop fields can benefit little from these interactions because they largely consist of single variety monocultures. Building evidence suggests that intraspecific (i.e., genotypic) diversity can be as important as plant species diversity in structuring arthropod communities and decreasing herbivore populations. We investigated the potential of increased crop genotypic diversity as a pest management tool using soybeans as a model system. To increase genotypic diversity, we planted plots with soybean cultivar mixtures. We compared field populations of soybean aphid (Aphis glycines) and natural enemies in low and high diversity plots across two years. Low diversity plots were created by planting monocultures of a single line, while high diversity plots consisted of all possible five-line mixtures chosen from a pool of six lines. These treatments were planted in replicated 30x30 foot plots. We assessed aphid populations weekly through whole plant counts and sampled natural enemies biweekly with sweep netting. Aphid populations did not respond to diversity, although low aphid populations restricted our ability to test our hypothesis under high pest pressure, which is when we expect diversity to have its greatest influence. Natural enemies did respond to increased diversity. Our results appear to indicate that increasing crop genotypic diversity holds promise as a management strategy for insect pests. Our research also builds on a growing body of research in natural and agricultural systems revealing the importance of intraspecific diversity.