The finding that the main pollinators of Drosera spp., Drosophyllum lusitanicum,
and Pinguicula spp. (i.e., large Diptera and Hymenoptera) are not captured by
adhesive trap leaves regardless of their degree of separation from the flowers has
two possible explanations. First, the adhesive traps only have a limited retention
capacity [32], meaning that large pollinators can escape after being trapped [18]. In a
comparison of the insect fauna that was captured by the trap leaves of Pinguicula
nevadense and model traps, Zamora [29] showed that P. nevadense captured prey
only below a specific size threshold (ca. 4 mm), while the model traps captured prey
that were 0–20 mm long, despite the composition of prey being similar for P.
nevadense and the model traps, suggesting that size is the principal factor determining the actual prey of carnivorous plants. Similarly, Gibson showed that body size
determines whether prey can escape from the trap leaves of Drosera filiformis and
Pinguicula lutea, with prey of <5–10 mm being unable to escape. Second, it is
possible that prey can recognize the visual and/or chemical signals of the adhesive
traps and avoid landing on these, as discussed in detail in Sect. 3.
2.2
Pitfall Traps
Carnivorous plants in the genus Nepenthes produce dioecious flowers and cannot be
self-pollinated. Therefore, when pollinator/pollen limitation exists, the trapping of
pollinators will lead to a reduction in fitness. The degree of pollinator trapping has
been investigated in N. gracilis growing naturally in Sumatra [33]. Flowers of this
species are pollinated by visiting pyramid moths (Herpetogramma sp., Pleuroptya
sp., Pagyda sp., Ambia sp., and Pycnarmon sp.) at night and calliphorid flies in the
evening, while ants are captured as the main prey with no pollinators being taken.
The pollinator fauna of several Nepenthes species has been shown to include Diptera
(for N. rajah [34], N. kinabaluensis [34], N. villosa [34], N. macfarlanei [35], and N.
mirabilis [36]), Diptera and Hymenoptera (for N. curtisii ssp. zakriana and N.
reinwardtiana [34]), and Coleoptera (for N. rafflesiana [37], mentioned in [35]).
Nepenthes spp. trap a broad range of insect taxa, but ants are usually abundant
among the prey items taken [38, 39]. Nepenthes rafflesiana has an ontogenetic
pitcher dimorphism, whereby the aerial (upper) and ground (lower) pitchers have
different morphologies and trap different types of insects, with many ant individuals
being trapped in both types of pitchers and a guild of generalist pollinator insects (e.
g., Lepidoptera, Thysanoptera, and Coleoptera) being trapped only in the aerial
pitchers [40, 41]. This trapping of generalist pollinator insects in the aerial pitchers
has been shown to be due to the secretion of volatiles [42] (see Sect. 3 for further
discussion). Therefore, there is a possibility that pollinator trapping could also occur
in the aerial pitchers.
In the genus Sarracenia, the degree of pollinator trapping has been investigated in
S. gracilis [7]. The pollinators of S. gracilis include the hymenopterans
Augochlorella aurata (1.5 Æ 0.48 visits/flower/h) and Bombus affinis (0.5 Æ 0.25
visits/flower/h) and the dipteran Fletcherimyia fletcheri (0.3 Æ 0.18 visits/flower/h),
while the prey species are mainly amphipods and ants. Therefore, pollinators are not
30 Pollinator Trapping in Carnivorous Plants
781
and Pinguicula spp. (i.e., large Diptera and Hymenoptera) are not captured by
adhesive trap leaves regardless of their degree of separation from the flowers has
two possible explanations. First, the adhesive traps only have a limited retention
capacity [32], meaning that large pollinators can escape after being trapped [18]. In a
comparison of the insect fauna that was captured by the trap leaves of Pinguicula
nevadense and model traps, Zamora [29] showed that P. nevadense captured prey
only below a specific size threshold (ca. 4 mm), while the model traps captured prey
that were 0–20 mm long, despite the composition of prey being similar for P.
nevadense and the model traps, suggesting that size is the principal factor determining the actual prey of carnivorous plants. Similarly, Gibson showed that body size
determines whether prey can escape from the trap leaves of Drosera filiformis and
Pinguicula lutea, with prey of <5–10 mm being unable to escape. Second, it is
possible that prey can recognize the visual and/or chemical signals of the adhesive
traps and avoid landing on these, as discussed in detail in Sect. 3.
2.2
Pitfall Traps
Carnivorous plants in the genus Nepenthes produce dioecious flowers and cannot be
self-pollinated. Therefore, when pollinator/pollen limitation exists, the trapping of
pollinators will lead to a reduction in fitness. The degree of pollinator trapping has
been investigated in N. gracilis growing naturally in Sumatra [33]. Flowers of this
species are pollinated by visiting pyramid moths (Herpetogramma sp., Pleuroptya
sp., Pagyda sp., Ambia sp., and Pycnarmon sp.) at night and calliphorid flies in the
evening, while ants are captured as the main prey with no pollinators being taken.
The pollinator fauna of several Nepenthes species has been shown to include Diptera
(for N. rajah [34], N. kinabaluensis [34], N. villosa [34], N. macfarlanei [35], and N.
mirabilis [36]), Diptera and Hymenoptera (for N. curtisii ssp. zakriana and N.
reinwardtiana [34]), and Coleoptera (for N. rafflesiana [37], mentioned in [35]).
Nepenthes spp. trap a broad range of insect taxa, but ants are usually abundant
among the prey items taken [38, 39]. Nepenthes rafflesiana has an ontogenetic
pitcher dimorphism, whereby the aerial (upper) and ground (lower) pitchers have
different morphologies and trap different types of insects, with many ant individuals
being trapped in both types of pitchers and a guild of generalist pollinator insects (e.
g., Lepidoptera, Thysanoptera, and Coleoptera) being trapped only in the aerial
pitchers [40, 41]. This trapping of generalist pollinator insects in the aerial pitchers
has been shown to be due to the secretion of volatiles [42] (see Sect. 3 for further
discussion). Therefore, there is a possibility that pollinator trapping could also occur
in the aerial pitchers.
In the genus Sarracenia, the degree of pollinator trapping has been investigated in
S. gracilis [7]. The pollinators of S. gracilis include the hymenopterans
Augochlorella aurata (1.5 Æ 0.48 visits/flower/h) and Bombus affinis (0.5 Æ 0.25
visits/flower/h) and the dipteran Fletcherimyia fletcheri (0.3 Æ 0.18 visits/flower/h),
while the prey species are mainly amphipods and ants. Therefore, pollinators are not
30 Pollinator Trapping in Carnivorous Plants
781