Insect pollinators in soybean fields: Community identification and sampling method analysis

Describing the flower-visiting insect community in soybean (Glycine max) fields is important for informing conservation decisions and assessing non-target risks to nectar and pollen feeding insects. Our objectives are to: 1) describe the pollinator community within soybean fields; 2) compare sampling methods for characterizing their abundance and diversity; and 3) identify species that visit soybean flowers. In 2011 and 2012, fields in Iowa were sampled during soybean flowering (R1-R6) using a sweep net, yellow sticky cards, and colored pan traps (i.e. bee bowls). Across locations and traps, 3,682 individuals and 38 species were collected with bees (Hymenoptera: Apoidea) accounting for 73%, syrphids (Diptera: Syrphidae) 12%, and other anthophilious Dipterans comprised 15% of the community. Abundance varied significantly across sampling methods, with the abundance of bees greatest in bee bowls (2011: P = 0.0341; 2012: P = 0.0016) and syrphids greatest on yellow sticky cards (2011: P = 0.0506; 2012: P = 0.0134). We only captured 16 flower-visitors (bees and syrphids combined) with a sweep net, representing less than 0.004% of the total captured. The abundance of bees and syrphids did not vary significantly with distance from field edge (P > 0.05). A subset of the most abundant bees carrying pollen was used to determine if bees were visiting soybean flowers. Soybean pollen was present on 29% of the bees with visible pollen loads. Further analyses of these data will be performed to determine, if species composition is consistent across years and the influence of edge-effects on the most abundant taxa.