Survey of insect pollinators in soybean fields: community identification and sampling method analysis

Describing the anthophilous insect community in soybean (Glycine max) fields is important for assessing non-target risks to nectar and pollen feeding insects, selecting surrogate flower-visiting insect species for laboratory and field-based studies, and for pollinator conservation. Our objectives are to: 1) describe the flower-visiting insect community within soybean fields; 2) determine the most effective sampling methods for characterizing their abundance and diversity; and 3) gain insight on species that visit soybean flowers. In 2011, fields in four Iowa counties were sampled during soybean flowering (R1-R6) using sweep netting, yellow sticky cards and colored bee bowls. Across locations and sampling methods 3,323 individuals and 33 species of flower-visiting insects were collected with bees (Hymenoptera: Apoidea) accounting for 34 percent, Syrphids (Diptera: Syrphidae) 30 percent and other anthophilous Dipterans 36 percent of the community. Abundance varied significantly across sampling methods for bees (P < 0.0001) and Syrphids (P < 0.0001) with the abundance of bees greater in bee bowls and Syrphids in yellow sticky cards. Further analysis showed that the bee abundance varied significantly with distance from the field edge (P < 0.05), but edge-effects on Syrphid abundance was not significant (P > 0.05). A subset of the most abundant bee species (n = 83 female bees) carrying pollen loads were used to determine if soybean flowers were being visited. Pollen grains were removed from bees, degreased and slide-mounted for analysis. Soybean pollen was detected on 29 percent of the bees tested. Future directions include repeating this study in Iowa and additional locations during the 2012 growing season.