Biology Reference
In-Depth Information
Table 8.3
Pollinators of
Arethusa
and
Pogonia
Orchid
Study
Location
Pollinators
Caste
Authors
Arethusa bulbosa
Bombus borealis
Kirby or
B. sandersoni
Franklin
Q
NL
Boland and Scott (
1991
)
B. ternarius
Say
Q
WI
Thien and Marcks (
1972
)
B. terricola
Kirby
Q
WI
Thien and Marcks (
1972
)
Pogonia ophioglossoides
Bombus borealis
Kirby or
B. sandersoni
Franklin
Q, W
NL
Boland and Scott (
1991
)
B. fervidus
(Fabricius)
X
ME
Heinrich (
1975
)
B. ternarius
Say
X
ME
Heinrich (
1975
)
Q, W
WI
Thien and Marcks (
1972
)
B. terricola
Kirby
X
ME
Heinrich (
1975
)
Q, W
WI
Thien and Marcks (
1972
)
B. vegans
Smith
X
ME
Heinrich (
1975
)
Q
WI
Thien and Marcks (
1972
)
Abbreviations:
Q
queen,
W
worker,
X
unspecified
by interfering with the developing pollen tubes from these grains; reduction in male
fitness can also result from wastage of pollen that could otherwise have been trans-
ferred to conspecific plants (Holsinger et al.
1984
; Lloyd and Webb
1986
;
Charlesworth and Charlesworth
1987
; de Jong et al.
1992
; Schoen and Lloyd
1992
;
Klinkhamer and de Jong
1993
; Snow et al.
1996
).
There is now reason to believe that pollinia placement also represents only one
of several factors restricting hybridization between
A. bulbosa
and
C. tuberosus
.
Seasonal isolation may be significant, at least in northern Wisconsin. The peak flow-
ering period for
A. bulbosa
is usually relatively early and only partially overlaps
that of
C. tuberosus
(Thien and Marcks
1972
). In addition, there may be partial
segregation based on pollinator size. The lip and anther cap are separated by a dis-
tance of about 5 mm in
A. bulbosa,
and only queens of
Bombus ternarius
Say and
B. terricola
were able to pollinate the flowers (Table
8.3
). Workers of these and
other bees were often too small to scrape the anther and remove the pollen. Thien
and Marcks (
1972
) found pollen of
C. tuberosus
on workers of
B. terricola
, on both
queens and workers of
B. ternarius
, and on queens of
Bombus vagans
and
Megachile
melanophaea
(Table
8.4
). They believe, however, that contrary to Dressler (
1981
),
the smaller workers were most effective at removing the pollen. Their emergence
coincided with anthesis in
C. tuberosus
when flowering in
Arethusa
was nearly
finished (Stoutamire
1971
; Thien and Marcks
1972
). The queens were much larger
and often too big to function as effective pollinators. Strong fliers, they were com-
monly able to prevent or delay the descent of the lip and to exit the flower before
contacting the stigma. When they did occasionally touch the column, they usually
had already begun their exit and only received pollen on their legs or on one side
of their thorax. Because of their size, they also tended to enter the flowers from
one side, and the pollinia were again inconsistently positioned. In either event,
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