Aphidophagous Predators in Iowa Soybean: A Community Comparison across Multiple Years and Sampling Methods

There is increasing evidence that Aphis glycines Matsumara (Hemiptera: Aphididae) populations are negatively impacted by endemic natural enemies within North America. In Iowa, surveys of natural enemies in soybean, Glycine max (L.) Merr., conducted before the arrival of A. glycines revealed a number of species that may contribute to their mortality. We used several sampling methods to determine the diversity of the natural enemy community in Iowa soybean since the arrival of A. glycines. Natural enemies were collected using fieldcounts (in situ sampling), destructive counts, sweep-net sampling, and yellow-sticky cards. When predaceous arthropods were combined across all sampling methods, six orders were identified, including nine families and 13 genera. In comparison with a similar study conducted 26 yr ago, we observed fewer native coccinellids with the most abundant being the exotics Harmonia axyridis (Pallas) and Coccinella septempunctata L. (Coleoptera: Coccinellidae). Combining all foliar-based sampling methods reveals a community of four aphidophagous taxa that account for >94% of the total captured: Toxomerus spp., H. axyridis, Orius insidiosus (Say), and Chrysoperla spp. In both years, destructive counts collected fewer species with more found using field-counts, sweep-net, and yellow-sticky cards. Sweep-net and yellow-sticky cards collected more agile life-stages and species as expected from sampling methods that rely on the insects’ activity/density to be effective. Our data suggest absolute methods such as destructive and field-counts may underestimate the contribution of mobile predators onA. glycines mortality.