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arguing that phenylalanine's most important effect for bees is its strong
phagostimulatory quality, which is unique among many amino acids tested
in other studies (Inouye & Waller, 1984). This quality certainly adds to the
taste of nectar (Gardener & Gillman, 2002), hence influencing bee prefer-
ences and the plant-pollinator food web structure at the community level.
Having such a potential, and owing to the high number of bee species in the
Mediterranean, it is not surprising that phenylalanine dominates the nectars
of plant species that are characterized by prevailing melittophily in this region,
especially in the Lamiaceae (Dafni et al., 1988; Petanidou & Ellis, 1993, 1996;
Petanidou & Vokou, 1993; Michener, 2000).
There are a few interesting species exceptions within the phenylalanine-
rich family of Lamiaceae. The first is Thymus capitatus with a detected
phenylalanine content at community average levels both in Israel and Greece
(Dafni et al., 1988; Petanidou et al., 2006). A possible explanation is that
T. capitatus constitutes a “pollinator sink” within both communities, visited by
mixed insect guilds (123 insect species in the Greek phrygana of which bees
comprise only 24%; Petanidou, 1991; Petanidou & Potts, 2006). It might be
that plants flowering outside the main blooming season under conditions of
little or no competition for pollinators, i.e., during the Mediterranean summer
or early spring (Petanidou, 1991, 2004), are less challenged to produce extra
phagostimulants, therefore have low levels of phenylalanine in their nectars
(e.g., Lamium amplexicaule in Athens and Rosmarinus officinalis in Israel,
as well as T. capitatus in both countries) (Dafni et al., 1988; Petanidou et al.,
2006). The exception of L. amplexicaule could also be explained by the
partly cleistogamous character of its flowers (Lord, 1982).
The case of GABA that is related positively with some insect guilds visit-
ing the phryganic plants may be similar to that of phenylalanine. Petanidou
et al. (2006) argue that phagostimulation may be related to the probable co-
presence of NaCl, a salt on which GABA strongly depends (Keynan &
Kanner, 1988; Wolfersberger, 2000). There is some evidence that NaCl has a
positive effect in attracting honeybees probably by improving nectar taste
(Taber, 1991; Fulton, 1997; Gardener & Gillman, 2002). Perhaps in an area
like the Mediterranean where sweetness can be of limited discriminatory
value (all nectars are concentrated, see also next paragraph), it is the combi-
nation of GABA-NaCl that constitutes the most important nectar
phagostimulant for several pollinating guilds (flies, bees, and beetles) that
might have acted as selective agents for GABA-rich nectars.
In addition to the effect that particular amino acids may have in attracting
pollinators to Mediterranean flowers, Petanidou et al. (2006) found that total
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