Pollen resources for pollinators in specialty oilseed crops

Simplified agroecosystems have depleted habitats for beneficial insects throughout the Midwest and Northern Great Plains of the USA. Beneficial insects include pollinators and natural enemies of crop pests, and both rely heavily on floral resources and habitat diversity to maintain healthy populations. Flower-rich and pollinator-friendly oilseed crops afford an opportunity to augment current crop rotations, allowing for a potential benefit to both producers and the beneficial insect community. Our study objectives were to determine insect visitation and floral resource production in specialty oilseeds, specifically pollen resources. Pollen is composed of many important macromolecules and minerals, with protein being particularly valuable for pollinators. Mass of pollen per hectare was calculated from measurement of pollen mass of freshly opened flowers and same day flower density. Protein composition of oilseed crop pollen was determined using the colorimetric Bradford assay, providing an estimate of crude protein resources available for pollen gathering insects. Pollen grains per flower declined as the oilseed crops completed flowering, coinciding with a decrease in flower density. The crop Echium plantagineum was estimated to have 0.5-17.0 kg/hectare of pollen available on a given day, totaling 330 kg/hectare over the entire season. Insect visitation was variable throughout the season, but crops such as calendula, which are known to produce little nectar, were visited quite heavily, suggesting pollen from this crop may be particularly attractive to certain pollinator groups. Pollen is a particularly important resource for bees, as it is used to provision brood cells in solitary species and for provisioning nurse bees which feed honey bee colonies. Adding specialty oilseed crops into current crop rotations will provide rich pollen sources to pollinating insects, aiding in efforts to promote pollinator health.