Evaluation location: Ohio, United States
A colony of soybean aphid (Aphis glycines Matsumura) was established in a growth chamber at Ohio Agricultural Research and Development Center (OARDC), Wooster, OH, during the summer of 2005 by collecting aphids from nearby soybean fields. The colony was maintained on seedlings of cultivar Williams 82 placed inside the growth chamber at temperatures between 22 and 24C with a photosynthetically active radiation of 330 umol m/2 s/1 for 15 h daily and 60 to 70% relative humidity. The colony was restarted on a fresh batch of seedlings every 3 to 4 wk by transferring aphids from the old seedlings to new ones. The experiment was conducted during September and October of 2005. Plants were grown in 10-cm-deep by 25-cm-wide by 50-cm-long plastic flats with a 8-cm space between plants and a 10-cm space between rows under 15 h light at approximately 24?C days and 9 h dark at 20?C nights. Each experimental unit was a row of three seedlings and five rows were accommodated in a flat. The experiment was arranged in a randomized complete block design (RCBD) with two replicates. At the V1-stage, seedlings were infested with 20 to 30 aphids of all developmental stages except the winged aphids by placing an infested leaf section between the petiole of the youngest expanding leaf and the stem. Aphids migrated to the leaves and stems of the seedlings within several hours after putting the infested leaf sections on the seedlings. The aphids were allowed to multiply and move freely among plants in the experiment. The plants were bottom watered to avoid disturbing the aphids. Fourteen days after infestation (DAI), each experimental unit was assigned an aphid score between 1 and 5, where 1 = <25 aphids per plant, 2 = 25 to 100 aphids per plant, 3 = 101 to 200 aphids per plant, 4 = 201 to 400 aphids per plant, and 5 = >400 aphids per plant. the LSD 0.05=0.6. Any score over 3.0 was considered highly susceptible.