Tribe Neottieae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 75

collected pollen as a larval food (Brantjes 1981 ). In apparent contradiction of the
reports from New England, the pollinia attached to the clypeus and distal fragments
were groomed in flight to the corbiculae. The basal parts of the pollinia remained on
the head and were available for pollination.
American authors agree, in general, with their European counterparts on the
usual sequence of events leading to pollination. The wasp grasps the distal part of
the lip and inserts its head under the column to feed on nectar contained in the
deeply concave basal section (Fig. 3.5c ). While doing so, pollinia borne from earlier
flower visits are brushed against the stigma, positioned just above the basal lip sec-
tion (hypochile). The amount of pollen deposited varies from a few hundred tetrads
to a whole pollinium. Additional feeding movements bring the wasp's head into
contact with the sticky rostellar fluid, which is extracted along with the adherent
pollinia as the wasp withdraws from the flower. Even though a caudicle is absent,
the pair of pollinia bend forward from the vertical as they dry, better positioning
them to contact the stigma of the next flower visited (e.g., Darwin 1862 ; Meeuse
1961 ; Judd 1972 ; Nilsson 1981a ; Richards 1986 ).
Wasps having fed on the nectar of this orchid sometimes become very lethargic
(Lojtnant 1974 ; Burns-Balogh et al. 1987 ; Muller 1988 ). Muller ( 1988 ) detected
small amounts of ethanol in the nectar, and Ehlers and Olesen ( 1997 ) have now
found ethanol-producing microorganisms present. These might be airborne or trans-
ported to the flower from various ripe fruits by wasps. Lojtnant ( 1974 ) observed that
“intoxication” of the wasps reduced the amount of pollen they groomed from their
bodies. He speculated that this might increase the quantity transferred to other plants
and that selection for the production of compounds with antimicrobial activity,
found in the nectar of some plants (e.g., Gilliam et al. 1983 ), might be absent in
E. helleborine (Ehlers and Olesen 1997 ).
More recently, Jakubska et al. ( 2005 ) detected the presence of other nectar com-
ponents with potential narcotic effects. These included indole, morphinan, and phe-
nol derivatives. They proposed that pollinators are first attracted to the flowers by
volatile nectar components, such as vanillin, furfural, ethanol, eugenol, and their
derivatives. Following nectar consumption, the narcotic effect of constituents, such
as morphinan and indole derivatives, may extend the time the pollinators spend on
the inflorescence and improve the chance of pollinating more flowers.
Jakubska et al. ( 2005 ) further suggested that because temperatures at their study
site (often exceeding 28°C or 82°F) would result in rapid evaporation of ethanol,
the level of ethanol production by microorganisms would have to be extraordinary to
produce its purported effect on pollinators. Moreover, a number of nectar compo-
nents, such as furfural, syringol, indol derivatives, eugenol, and methyleugenol, pres-
ent in the nectar of E. helleborine , have known bactericidal and fungicidal properties.
The species of Cladosporium and Candida found by Ehlers and Olesen ( 1997 ) are
apparently susceptible to these compounds. The contribution of these microbes to the
“intoxication” of pollinators may, therefore, be less significant than these authors
suggest. Ethanol could, however, derive from the decomposition of some nectar com-
ponents and might therefore still contribute to the lethargic behavior of pollinators.