Soybean and Bees

flowered varieties are inter-mixed in the same row in opposition to separate row plantings
(Beard and Knowles, 1971).
Soybean flowers are not always attractive to honeybees, leading to the hypothesis that environmental
conditions during growth and flowering of plants affect the development of
flower characteristics (Robacker et al. 1983). In general, plants that grow in higher temperatures
produce more nectar and are more attractive than those grown in cooler climates, up
to a maximum of 29° C. Erickson et al. (1978) also observed that it was necessary to consider
that the attraction of the soybean to honeybees was not the same for all varieties. Jaycox
(1970b) found that number of bees varied from 680 to 810/ha, depending on the soybean cultivar,
which represents roughly 1% of the population found on alfalfa (Pedersen, 1962), or
20% of the population observed on white clovers (Weaver, 1965).
It is worth mentioning that, although the potentiality for nectar secretion (meaning attractiveness
to bees) is hereditary, it is largely subject to climatic and edaphic aspects. Another
factor that may influence the attractiveness of soybeans to bees is the distribution of flowers
on the plants. The flowers of soybeans are not grouped into large heads and racemes as
in clover and alfalfa, but instead are located at the leaf nodes of the plants. They are usually
beneath the foliage on indeterminate cultivars. Heinrich and Raven (1972) point out that inflorescences
enable a large pollinator, such as a bee, to meet its energy demand from a group
of flowers that would be unsuitable individual1y. The amount of energy expended in walking
between flowers can be 100 times less than an equivalent period of flight.
Even though honeybees do walk between flowers at soybean nodes and possibly between
closely spaced nodes, the number of soybean flowers per plant is low. Therefore, more flying
would be required to visit a given number of flowers on soybeans than on crops such as alfalfa
or clover, justifying the highest number of bees visiting these crops, as contrasted with
soybeans.
It is important to consider that the soybean flower stigma becomes receptive one or two
days before anthesis, while the anthers release the pollen before the flower opens, which are
essential conditions for auto pollination (Fehr 1980; Delaplane and Mayer 2000). According
to Yoshimura (2011), wind pollination is negligible due to the restricted range of soybean pollen
dispersal and its short life.
Milfont (2012) refers that auto pollination and use of pesticides in soybean, including the period
when flowers are present, created the sense that soybeans do not need (or benefit from)
insect pollination.
86 SoybeAn and bees