Pollination Vectors
German Roitman (Mon, 12 May 2008 16:34:36 PDT)

Dear Jim:

I have been searching in some databases of
pollination and the info available refers that
Trillium is self sterile (it need the activity of
pollinator for seed set) and most species are
pollinated by bumblebees, flies, ants and
beetles. The fly you have observed is probably a
Syrphid fly not a Drosophila, i guess. Syrphid
flies use to eat pollen and pollinate as well.

You can check this publication for more information and references:
___________________________

Tammy L. Sage, Steven R. Griffin, Vincenza
Pontieri, Peter Drobac, William W. Cole and
Spencer C. H. Barrett 2001. Stigmatic
Self-Incompatibility and Mating Patterns in
Trillium grandiflorum and Trillium erectum(Melanthiaceae)
Annals of Botany 88: 829-841

Post-pollination processes governing mating
patterns in Trillium, a well-known genus of
insect-pollinated woodland herbs, are poorly
understood. Mechanisms influencing outcrossing
were investigated in T. grandiflorum and T.
erectum, two widespread species native to eastern
North America. In southern Ontario, Canada, the
two species are often sympatric; they flower in
early May, and are pollinated by different
assemblages of insects. Controlled cross- and
self-pollinations and structural observations of
pollen germination and pollen tube growth were
conducted to determine whether the two species
possess a self-incompatibility (SI) system and,
if so, the specific site(s) of self-rejection.
Controlled pollinations indicated that both
species set significantly more seeds from
cross-pollination than self-pollination,
implicating the action of SI. This was confirmed
by structural studies which demonstrated that
self-recognition and rejection reactions occurred
on dry-type stigmatic papillae. Observations of
pollen hydration revealed that self-rejection was
rapid, being initiated within 10 min of
pollination and prior to pollen tube emergence.
Final self-rejection resulted in failure of
pollen tube growth at the base of stigmatic
papillae. SI was expressed more weakly in T.
erectum and thereby resulted in considerable
self-seed set in some individuals . Estimates of
outcrossing rates using allozyme markers
indicated that T. erectum displayed a
mixed-mating system whereas T. grandiflorum was
more highly outcrossed. Structural studies of
pollen traits indicated that the two species
differed with respect to the size of grains and
their aggregation with implications for pollen
dispersal and mating. The ecological and
evolutionary implications of the variable
expression of SI in Trillium are discussed.

____________________

In your case if the 2 species of Trillium has
diferent pollen shape (color, size, etc), perhaps
you can capture the flies using a dry method so
pollen is not washed and then extract the pollen
from the bodie of the flie and observe it using a
microscope, in that way you can see if the flies
visit the 2 species or only one of them.

Hope this help

Best wishes

Germán

At 11:19 11/05/2008, you wrote: