Soybean and Bees

The attractiveness of a bee to a plant is largely linked to the concentration of sugars in nectar,
which can vary widely (2-3 to 75-77%) on the secreted nectar. Bees prefer the most concentrated
nectar because they spend less time and less work to dehydrate to turning it into
honey. According to Erickson (1975a), the mean quantity of dissolved solids in the nectar
recovered from bees foraging on soybeans was 37% (range 18-55%; n = 30). The concentration
of solids was lowest in the morning and increased as the day progressed. Concurrent
samples were obtained from bees foraging on alfalfa for comparison purposes. In spite of being
a known preferred flower, alfalfa nectar had lower solid soluble concentrations (Table 7).
Table 7. Soluble solids on the nectar of soybeans and alfalfa, by time of the day.
Time
Soybeans
Alfalfa
Mean (%) Range (%) Mean (%) Range (%)
10 AM 34 18-43 28 22-34
12 noon 37 31-52 25 22-30
02 PM 40 23-55 30 21-41
Source: Erickson, 1975a
Robacker et al. (1983) investigated the effects of environmental conditions on flower characteristics,
including flower production, color intensity, openness, size, nectar secretion and
aroma emanation and on attractiveness of the plants to honeybees. Most flower characteristics
increased the attractiveness as day air temperatures at which plants were grown increased
from 20 °C to 24 °C, and reached maximum values at 28 °C before plateauing or declining
at 32 °C, although flower size and nectar secretion continued to increase as growing
temperature raised beyond 32 °C.
Of the two flower aroma components, emanation of one component increased while the other
decreased with the elevation of the growing temperatures (Robacker et al., 1983). The
suggested hypothesis is that the two aroma chemicals may communicate flower-readiness
information to pollinators. Flower production and flower openness responded linearly to
night air temperature at which plants were grown, attaining highest values at higher (22
°C, 26° C) vs. lower (14 °C, 18 °C) temperatures. Flower production also responded linearly
to soil temperature, attaining highest values at higher (28 °C - 32 °C) vs. lower (16 °C - 20 °C)
temperatures.
Of the two levels each of N (75 ppm and 175 ppm) and P (15 ppm and 30 ppm) tested, the higher
level of N stimulated greater flower production, flower size and nectar secretion while the
higher level of P decreased the same three flower characteristics, according to Robacker et
SoybeAn and bees
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