2.1
Adhesive Traps
In the genus Drosera, the degree of pollinator trapping has been investigated for
eight species: four species that separate the rosette-shaped trap leaves from the
flowers through the production of long flower scapes and four species that have
stems supporting both the flowers and trap leaves in close proximity (two of which
have small, round trap leaves and two of which have vertically developed, linear trap
leaves) (Table 1). Six of these species use large- to medium-sized Diptera
(Syrphidae, Bombyliidae, Calliphoridae, Tachinidae, and Muscidae) as pollinators,
while the remaining two use Coleoptera, and all eight species tend to take small
Diptera (mainly Nematocera) and terrestrial-dwelling invertebrates as prey. Therefore, regardless of the degree of separation of the flowers and trap leaves, many of
these species do not trap any pollinators or only trap pollinators at quite a low level.
The exception to this is D. makinoi, in which effective pollinators, including large
Diptera and Hymenoptera, are captured throughout the flowering season [22]. The
flowers and trap leaves are remarkably close to one another in this species, so it is
considered that pollinators visiting the flowers are accidentally trapped due to the
morphological characteristics of the plants. However, since D. makinoi is selfcompatible and self-pollinated flowers can make similar amounts of seed as
outcrossed flowers (Watanabe, unpublished data), pollinator trapping may not
reduce the fitness of this species. Interestingly, D. toyoakensis, which has similar
morphological characteristics to D. makinoi, has a relatively low level of pollinator
trapping (see Sect. 6), and the inbreeding coefficients of these species reflect this
situation (D. makinoi, 0.497; D. toyoakensis, 0.260; Watanabe, unpublished data).
In Drosophyllum lusitanicum, the main pollinator fauna is Coleoptera (Enicopus
sp., 56.6% of flower visits) and Hymenoptera (Panurgus sp., 25.6% of flower visits),
while the main prey fauna is small Diptera (83.5%), so the main pollinators were not
trapped [23].
In the genus Pinguicula, the degree of pollinator trapping has been investigated in
P. vallisneriifolia [11]. According to this study, the degree of pollinator trapping and
its fitness consequences varies depending on the shadiness of the microsites where
the plants grow. Large Diptera (Bombylius sp.) and Hymenoptera (Lasioglossum sp.
and Anthophora sp.) visit flowers only in sunlit sites and are not captured by trap
leaves. By contrast, small Thysanoptera (Taeniothrips meridionalis) and Coleoptera
(Eusphalerum scribae) visit flowers and are frequently captured by trap leaves
regardless of the shadiness of the microsites. Thus, the trapping of Thysanoptera
and Coleoptera at shaded sites may lead to a reduced fitness because there are no
other efficient pollinators at these sites, whereas the trapping of these insects at sunlit
sites may have no effect on fitness because the more efficient dipteran and hymenopteran pollinators remained untrapped. The main pollinators of other species in
the genus Pinguicula include Hymenoptera (for P. ionantha, P. lutea, and P.
planifolia [24]; and P. longifolia [25]), Diptera (for P. alpina and P. vulgaris [26]),
and Lepidoptera (for P. moranensis [27]), while the main prey are tiny invertebrates
such as Collembola, Acarina, and Nematocera [28–31]. Consequently, Pinguicula
spp. do not capture medium–large pollinators.
778
K. Tagawa
Adhesive Traps
In the genus Drosera, the degree of pollinator trapping has been investigated for
eight species: four species that separate the rosette-shaped trap leaves from the
flowers through the production of long flower scapes and four species that have
stems supporting both the flowers and trap leaves in close proximity (two of which
have small, round trap leaves and two of which have vertically developed, linear trap
leaves) (Table 1). Six of these species use large- to medium-sized Diptera
(Syrphidae, Bombyliidae, Calliphoridae, Tachinidae, and Muscidae) as pollinators,
while the remaining two use Coleoptera, and all eight species tend to take small
Diptera (mainly Nematocera) and terrestrial-dwelling invertebrates as prey. Therefore, regardless of the degree of separation of the flowers and trap leaves, many of
these species do not trap any pollinators or only trap pollinators at quite a low level.
The exception to this is D. makinoi, in which effective pollinators, including large
Diptera and Hymenoptera, are captured throughout the flowering season [22]. The
flowers and trap leaves are remarkably close to one another in this species, so it is
considered that pollinators visiting the flowers are accidentally trapped due to the
morphological characteristics of the plants. However, since D. makinoi is selfcompatible and self-pollinated flowers can make similar amounts of seed as
outcrossed flowers (Watanabe, unpublished data), pollinator trapping may not
reduce the fitness of this species. Interestingly, D. toyoakensis, which has similar
morphological characteristics to D. makinoi, has a relatively low level of pollinator
trapping (see Sect. 6), and the inbreeding coefficients of these species reflect this
situation (D. makinoi, 0.497; D. toyoakensis, 0.260; Watanabe, unpublished data).
In Drosophyllum lusitanicum, the main pollinator fauna is Coleoptera (Enicopus
sp., 56.6% of flower visits) and Hymenoptera (Panurgus sp., 25.6% of flower visits),
while the main prey fauna is small Diptera (83.5%), so the main pollinators were not
trapped [23].
In the genus Pinguicula, the degree of pollinator trapping has been investigated in
P. vallisneriifolia [11]. According to this study, the degree of pollinator trapping and
its fitness consequences varies depending on the shadiness of the microsites where
the plants grow. Large Diptera (Bombylius sp.) and Hymenoptera (Lasioglossum sp.
and Anthophora sp.) visit flowers only in sunlit sites and are not captured by trap
leaves. By contrast, small Thysanoptera (Taeniothrips meridionalis) and Coleoptera
(Eusphalerum scribae) visit flowers and are frequently captured by trap leaves
regardless of the shadiness of the microsites. Thus, the trapping of Thysanoptera
and Coleoptera at shaded sites may lead to a reduced fitness because there are no
other efficient pollinators at these sites, whereas the trapping of these insects at sunlit
sites may have no effect on fitness because the more efficient dipteran and hymenopteran pollinators remained untrapped. The main pollinators of other species in
the genus Pinguicula include Hymenoptera (for P. ionantha, P. lutea, and P.
planifolia [24]; and P. longifolia [25]), Diptera (for P. alpina and P. vulgaris [26]),
and Lepidoptera (for P. moranensis [27]), while the main prey are tiny invertebrates
such as Collembola, Acarina, and Nematocera [28–31]. Consequently, Pinguicula
spp. do not capture medium–large pollinators.
778
K. Tagawa