Cover crops as an early-season resource for native bees in temperate annual cropping systems

This research aims to evaluate the potential benefits and trade-offs associated with adoption of cover crops in temperate annual cropping systems for native bee conservation.  With the current issues facing managed honeybee colonies, the conservation of native bee communities is critical to maintaining pollination services.  However, native bees are negatively affected by agricultural intensification.  Overwintering cover crops are often employed for soil conservation and fertility, but little data exist on flowering cover crops as a potential resource for native bees in annual cropping systems where springtime flowers may be spatially and temporally sporadic.  This project evaluates canola (Brassica napus), red clover (Trifolium pratense), and Austrian winter pea (Pisum sativum subsp. arvense), three commonly used overwintering cover crops, established over four fall planting dates, for use by bees.  Visitation to each crop was compared to landscape-level trapping to evaluate actual versus potential use over time.  Additionally, we monitored onset and density of bloom as it related to bee visitation and planting date.  Each crop was studied independent of cash crop plantings to determine bee use within a variety of crop rotations as well as what potential floral resource would be lost by pre-bloom or early-bloom cover crop termination.  Canola, the earliest crop to flower, provided a floral resource to the widest diversity of native bees, followed by Austrian winter pea and red clover.  In conclusion, overwintering cover crops, when planted in a rotation that allows for sufficient bloom, may provide early-season nutritional resources for bees in agricultural landscapes.