Survey of Bees (Hymenoptera: Apoidea) in Flowering Soybean and Sunflower Fields in North Dakota

Bees are declining in the U.S., especially in heavily cropped landscapes due to habitat loss, pesticide use, and other factors. In Midwestern states like North Dakota (ND), where field crops are grown extensively, native resources for bees are often sparse. Soybean and sunflower are two major crops grown in ND which could provide floral resources for bee communities. To address the importance of these crops for bees, we sampled soybean and sunflower fields in 2018 using bee bowls. Our objectives were: 1) to determine the community composition, abundance, and species richness of bees in flowering soybean and sunflower grown in southeastern ND; 2) to determine the bee abundance at different flowering stages of each crop; and 3) to evaluate the effectiveness of bowl colors for monitoring bees. We collected a total of 3,038 bees and 53 different species. Apidae was the most common bee trapped across both crops with 82.4% of collected bees. Overall, community composition, abundance, and species richness of bees were not significantly different between crops; however, abundance indicated that 116.8% more bees were collected in soybean than sunflower. Regardless of crop, bee abundance at field edges was 18.2% higher than those captured from field interiors; however, species richness did not differ between field edges and interiors. Bee abundance did not differ across flowering stages of either crop, with one exception in sunflowers. Sunflower at R6 (flowering completed) had much higher bee abundance than sunflower at R5.5 (mid-flowering), probably due to the bowls being more attractive and visible as flowering ended. Blue bowls captured the majority of bees. Both blue and yellow bowls captured significantly more bees than white and red bowls across both crops. The relative bee diversity and abundance identified in this study increased our knowledge of bee communities in soybean and sunflower grown in ND.