Soybean and Bees

in seeds, particularly at intermediate levels of nectar replenishment. The maximal potential
seed set was reached when flowers received intermediate levels of pollen addition and nectar
removal; however, when the frequency of nectar removal was increased seed production
decreased to levels similar to naturally pollinated flowers. These results suggest that P. roseus
seed production is pollen limited in both populations, and that the magnitude of pollen limitation
was more pronounced when plants paid the cost of attracting additional pollination
(nectar replenishment costs).
Although some animal-pollinated flowers respond positively to nectar removal by producing
additional nectar, this extra secretion is not always expensive (Ordano and Ornelas,
2005). The expenses of nectar production are negligible in terms of both floral tissue investment
(Harder and Barrett 1992; Leiss et al. 2004), vegetative growth (Golubov et
al. 2004) or in seed production (Ordano and Ornelas 2005; Ornelas et al. 2007), in spite
that it can also be reasonably high in terms of devoted energy, photosynthate assimilation
(Pleasants and Chaplin 1983; Southwick 1984) or seed production (Pyke 1991; Ordano
and Ornelas 2005).
Pyke (1991) demonstrated the costs of nectar production in wild plants of Blandfordia nobilis,
which were hand-pollinated to ensure optimal pollination. His results showed that availability
of resources and not the level of pollination limit the number of seeds per plant.
Some studies have shown a peak in seed production at intermediate levels of pollinator
visitation, with a decrease in seed production at higher visitation levels (Búrquez et al.,
1987; BÚRQUEZ and CORBETT, 1991; Young, 1988; Herre, 1990) that may result from
the removal of previously deposited pollen on the stigma (Gori, 1983). In addition, pollen
deposition is variable from one flower to another (Stephenson 1981; Burd, 1995).
These results might indicate saturation of bee population foraging in the field, collecting
more nectar and more pollen than advisable, forcing the plant to invest resources
to produce more nectar, or preventing maximum potential of fecundation. This kind of
result is contrarily to the idea that more bees foraging on soybean would result in more
cross-pollination, more efficiency on fecundation, at last higher yields.
Nectaries
Nectaries can be extremely diverse with respect to their localizations, structures and even
their secretion mechanisms, according to Elias (1983), Fahn (1988) and Pate et al. (1985).
In some species there is no externally visible structure for a nectary (Frey-Wyssling and
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