Field experiments were conducted in the Biodiversity
Study of the Kellogg Biological Station-Long Term Ecological
Research site (KBS-LTER, Hickory Corners, MI),
during 2004 and 2005. The KBS-LTER station characterizes
typical SW Michigan conditions, with crop yields representative
of the US North Central Region (Robertson
et al., 2000). The biodiversity study has a series of 21 different
agronomic treatments that vary in plant species diversity
in time and space, ranging from 0 to >15 species in
3-year rotation cycles (http://lter.kbs.msu.edu/). Treatments
are replicated in 4 completely randomized blocks
in 9.1 27.4 m plots, resulting in a large mixture of crops
in a relatively small area. This diversity of habitats favors
the presence of multiple natural enemy species that may
potentially impact A. glycines, including several species of
generalist parasitoids (Kaiser et al., 2007). Within this site,
we utilized the 3 most similar treatments (all typical corn–
soybean–wheat rotations) that varied only in the presence
of cover crops in the non-soybean portions of the rotations.
These included a system with a legume and a small grain
cover crop in corn and wheat, a system with only a legume
cover crop in corn, and finally a system with no cover crop.
Our rationale in selecting these systems was primarily to
increase replication (i.e. 4 blocks 3 agronomic treatments
= 12 plots), rather than