2. Methods
2.1. Rearing
Soybean plants var. 92B16 (Pioneer Hi-Bred International Inc., Johnston, IA) were maintained in a green house at 24 °C on a 16:8 h L:D. Soybean aphid was cultured on soybean in a walk in growth chamber (Percival Scientific, Perry, IA) at 24:16 °C on a 16:8 h L:D. The predatory midge, A. aphidimyza, was obtained from IPM Laboratories (Locke, NY) as pupae. Flies were hatched by placing the pupae into a dark growth chamber for 48 h at 24 °C. Adults were released onto soybean aphid infested soybean plants and allowed to lay eggs.
Larvae hatched within 3 d and reached their second instar within 5 d. The aphid predator C. carnea was obtained from Koppert Biological Systems (Ann Arbor, MI) as eggs and first instar larvae. The eggs and larvae were placed in rearing boxes on soybean plants infested with A. glycines.
A culture of H. axyridis was initiated by field-collecting adult beetles from soybean
fields at the Michigan State University Beet and Bean Farm (Saginaw, MI); larvae
and adult H. axyridis were reared separately on soybean aphid-infested plants.
All predator colonies were maintained at 24:16 °C on a 16:8 h L:D.