Tribe Neottieae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 69

most frequently, Sphaerophoria philanthus Meigen. A closely related, nonsyrphid
pollinator, Copestylum satur (Sacken), was also captured. Wasps were occasionally
trapped, but none carried any pollen. However, Mantas ( 1993 ) identified yellow
jackets ( Vespula vulgaris ) as pollinators at sites in northwestern Montana ranging in
altitude from 945 to 990 m.
Ross ( 1988 ) also saw syrphid flies depositing eggs in flowers of E. gigantea at
widespread sites from Del Norte County, California, to Zion Canyon, Utah. He
reported many flies entering or leaving the flowers and many hovering in the vicin-
ity with one or two yellow pollinia attached to their dorsal thoraxes (Fig. 3.4d ).
After landing on the epichile, the fly crawled under the column, its thorax brushed
against the stigma, and picked up a deposit of rostellar glue. When it later backed
out of the flower, the sticky deposit contacted and extracted pollinia from the anther.
0OLLINATIONOCCURREDDURINGTHEENTRYOFSUBSEQUENTLYVISITEDmOWERS
Wilson ( 2009 ) observed similar behavior at her Colorado sites. The pollinators
revisited many flowers but usually moved from the bottom of the inflorescence
upward, spending 1-3 s on each open flower. If, as Wilson reported, the plants are
not protandrous, the direction of pollinator movement would not affect the levels of
geitonogamy or outcrossing. The pollinia were received on the thorax with some
syrphids carrying two or more sets. Flies occasionally deposited eggs on the peri-
anth. However, like Ross ( 1988 ), Wilson noted that aphids or aphid eggs were usu-
ally not present on the flower or other parts of the plant, and the hatched syrphid
larvae would therefore not survive.
Ivri and Dafni ( 1977 ) and Sugiura ( 1996 ) reported a similar strategy in the nec-
tar-producing orchids, E. helleborine (L.) Crantz subsp. helleborine in Israel and
E. thunbergii A. Gray in Japan. In addition to male syrphids that sometimes fed at
and pollinated the flowers, females laid eggs on the labellum. The hypochile, as in
E. gigantea , bears warts or markings on its surface that may mimic the shape and
color of aphids, and these, along with the nectar, are thought to attract the females.
Feeding behavior, before or after egg laying, may lead to pollination of the flower.
The presence of a mimetic system in a rewarding orchid might perhaps be thought
of as a supplementary pollinator attractant, effecting a net increase in pollination
and reproductive success. Attraction by deceit in rewarding orchids is known else-
where as, for example, in Epidendrum amphistomum A. Rich., where male moths
are lured by production of a pheromone mimic but pollination is accomplished
during nectar feeding not pseudocopulation (Adams and Goss 1976 ).
In some species of Epipactis , insect-induced movements of the distal labellar
segment are thought to play a role in pollination, changing the position or affecting
the balance or exit trajectory of the pollinator and thus bringing it into contact with
the column (e.g., Darwin 1862 ; Sugiura 1996 ). This subject needs additional study,
but Nilsson ( 1981a ) called attention to an apparent correlation between pollinator
species and the development of the labellar hinge mechanism. E. gigantea has a
well-developed labellar hinge, and its rotation could play a role in effecting contact
between the thorax of the visiting syrphid fly and the column.