SOYBEAN and BEES

honeybees can discriminate between sucrose concentrations differing by only 5%. They
showed that bees can distinguish between 50% and 45%, but not between 50% and 47.5% or
between 47.5% and 45% sucrose.
Carbohydrates and free amino acids in the nectar are paramount for attraction, but
because animals differ in their nutritive preferences, the composition of the nectar
determines the spectrum of its consumers. For example, hummingbirds, butterflies,
moths and long-tongued bees usually prefer sucrose-rich FNs, as do most ant species
that feed on EFN, whereas short-tongued bees and flies prefer FN rich in hexoses
(Gonzales-Teuber and Heil, 2009a; Nepi and Stpiczynska, 2008; Nepi et al., 2009;
Blütgen and Fiedler, 2004). However, some nectarivorous birds and ants lack the
enzyme invertase, being not able to process sucrose, thus preferring sucrose-free nectars,
according to Heil et al. (2005) and Martínez del Río (1990).
Previous studies reached quite different conclusions. Whitehead and Larsen (1976) determined
that the maximum response of honeybee galeal chemoreceptors occurs with
sucrose concentrations of about 1.5 molar (50% w/w) and glucose or fructose concentrations
of about 3.0 molar (50% w/w). Honeybee carbohydrate preferences, based on nectar
contents of plant species preferred by bees, indicated that honeybees might prefer
nectar with relatively equal quantities of fructose, glucose, and sucrose (Furgala et
al., 1958; Kropacova, 1965). However, Wykes (1952) examined the gustatory response
of honeybees to sugar solutions varying in composition but having the same total sugar
concentration, showing that honeybees prefer solutions of sugars in this descending
order: sucrose, glucose, maltose, and fructose. Bachman and Waller (1977) and Waller
(1972) showed that honeybees prefer sugar solutions in which sucrose is both the main
constituent and is near a concentration of 50%.
Besides carbohydrates and amino acids, which are present in high proportion in nectar, other
compounds are involved in the nectar capacity of attraction. Volatile organic compounds
(VOCs), like benzyl acetone, have been related to pollinator attraction, and scented petals
have been known for centuries. In line with this information, nectar odors are considered a
relevant signal for pollinators (Raguso, 2004). On the other side, gelsemine and iridoid glycosides
exhibit repellent properties (Heil, 2011).
Weiss (2001) demonstrated that butterflies and moths prefer artificial flowers containing
scented nectar in contrast with ones containing pure sugar solutions, while Röse et al. (2006)
mentioned that parasitoid wasps localize cotton (Gossypium hirsutum) EFN using only its
odors, the same for mites that use nectar odors to distinguish between host and non-host
plants, according to Reyneman et al. (1991).
70 SoybeAn and bees