Quantitative and Qualitative Variation in Floral Nectar of Soybean Cultivars in Southeastern Missouri 1

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Abstract
Nectar characteristics of 17 soybean ( Glycine max [L.] Merr.) cultivars grown in Hayti, Mo., were examined in order to assess the potential for preferential foraging by honey bees ( Apis mellifera L.). Nectar secretion occurred between ca. 0900 and 1500 h Central Daylight Time; individual flowers bloomed only one day. Mean nectar production per flower varied from 0.022 to 0.127 µl among cultivars, while total nectar carbohydrate content varied from 301 to 1,354 µg/µl. Fructose, glucose, and sucrose content varied from 42 to 314 µg/µl, 43 to 262 µg/µl, and 97 to 986 µg/µl, respectively. Total carbohydrate per flower varied from 16.0 to 134 µg. The ratios of fructose: glucose: sucrose among cultivars were distributed along a broad continuum, from those with low sucrose (ca. 1.2:1.0:1.4) to those with high sucrose (ca. 1.2:1.0:6.7). When compared as two distinct groups, there were no apparent differences in nectar characteristics among white-flowered and purple-flowered cultivars. Time of day was the primary factor affecting soybean nectar characteristics; nectar fructose, glucose, sucrose, and total carbohydrate content all increased with time of day, while the volume of nectar per flower decreased. Day-to-day and temperature effects on nectar characteristics were minimal. Comparisons made within individual sampling periods suggest that there are differences in nectar characteristics among cultivars which could encourage preferential foraging by honey bees.