Tribe Calypsoeae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 119

Fig. 6.4 Pseudaletia
unipuncta (army worm),
a pollinator of Tipularia
discolor , dorsal view, scale
bar = 5 mm
Whigham and McWethy ( 1980 ) suggested that self-pollination might occur
when, following attachment of the viscidium to the moth's eye, the insect forces its
head deeper into the flower. This would bring the pollinia into contact with the
sticky stigmatic surface, positioned just posterior to the anther sac. However,
because the surface of the viscidium is turned inward and faces the center of the
flower, it probably is affixed to the back of the compound eye as the moth withdraws
(Catling and Catling 1991 ). Even if the viscidium is attached as the moth enters the
flower, the anther cap, which surrounds the four pollen masses on the end of the
pollinarium (Fig. 6.3c ), is retained for 8-40, usually 15-20 min following extrac-
tion, and pollinia are not generally deposited on a stigma until after the anther cap
falls off (Snow and Whigham 1989 ; Catling and Catling 1991 ). Since the moths
quickly visit only a few flowers on any given inflorescence before moving on to
another plant, the period of anther cap retention provides a mechanical barrier dur-
ing this interval that should prevent or greatly reduce the chances of selfing and
promote outcrossing (Stoutamire 1978 ; Whigham and McWethy 1980 ; Snow and
Whigham 1989 ; Catling and Catling 1991 ). No data are available on possible return
visits to the same flower. Following loss of the anther cap (Fig. 6.3d ), one or two of
the four transported pollinia may attach to and remain on any contacted stigmatic