Acta
Bot.
Neerl. 37(2), June 1988,
Pollination
153-163
p.
ecology and seed-set
species Melampyrum
L.
arvense
in the
rare
annual
(Scrophulariaceae)
M.M. Kwak
Department ofPlant Ecology, University ofGroningen, Biological Centre,
9750
P.O. Box
14,
(Gn), The Netherlands
A A Haren
SUMMARY
Pollination of
annual,
Melampyrum
in
investigated
was
L.,
arvense
large-flowered hemiparasitic
a
in The
populations
Netherlands, Germany,
France and Switzerland. Pollination is achieved
by bumblebees,
varying tongue lengths, collecting pollen and/or
nectar.
the flower
medium-tongued workers pollinate
thorax
pollination)
and
of fluorescent
robbing
was
present
and
a
is
in
a
and sometimes also
volume of 0-26 pi, with
ratio of fructose:
but
self-fertile,
glucose:
of auto-deposition.
sucrose
flowers do
caged
sugar
=
the
nectar
by
Nectar
pistil.
concentration of 30%
l:0-67:0-73. M.
produce
not
collect
destroying
a
bumblebees
the actual transfer
analysed by
as
powder. Short-tongued bumblebees
flowers,
the
nototribically (head-
pollen-collecting short-tongued
sternotribically (venter pollination),
with
and
Long-
seeds
by
arvense
the absence
Artificial pollination showed that increasing
pollination intensity
increased
pollinations fruiting
did
not
fruiting, although
after three
increase and the number of seeds per fruit
did.
Observations in
a
with variable
plots
low visitation intensity,
the flower’s life
span
flowers
(7 days),
times. The additional effect
during
highly
the flower’s lifetime
branched in
plants, resulting
branches
produce
production
had
a
in
per
rather
compared
and
on
more
more
at a
seeds per
M.
in
three French
flower,
seed
showed that
during
least 6-7 times during
visitation intensity
39-3
pollination
low-density plots
are
of
and the fact that flowers
on
influence the total seed
population
arvense
and seed
in The Netherlands
production
per
plant
populations.
Key-words: bumblebees, Melampyrum
robbery,
at
high density. Branching
plant,
high fruiting percentage
to
high
low. Plants in
plants
flowers per
plant. The
visited
the seed-set of one-hand
was
contrast to
plant density
were
arvense,
nectar,
pollination,
production.
INTRODUCTION
The genus
areas
of
extending
20-30
Melampyrum (Scrophulariaceae, Rhinanthoideae,
distribution,
into
one
tropical
in
Europe extending
regions.
distribution in North America
Melampyrum
arvense
L.,
One
(for
a
species,
review
field cow-wheat, is
on
a
153
into
Asia
and
Melampyrum
population
hemiparasitic,
species)
the
other
lineare
biology
annual
has
Desr.,
see
Ter
species,
two
main
in East Asia
has
Borg
wide
a
1985).
which is
very
154
M. M. KWAK
in The
rare
it is restricted
Netherlands;
also found in
and France,
where it is
the southern parts
to
countries such
neighbouring
more
but also
common,
has
characteristic species of Caucalidion (Hartl 1974). M.
semi-dry
sites. It is foundon road verges,
in cereal
occasionally
cleaning
fields,
cereal caryopses. The
reduction in the
the
Although
low
a
of farm
margins
frequency.
prefers
arvense
al.
M.
warm
chalk
lanes,
have the
arvense
decrease in the number of
recent
habitats
possible
et
1980).
is
arvense
dry
sunny,
grasslands
It is
1986)
a
to
and very
the main habitat in the
before efficient methods of seed
past
introduced. The seeds of M.
were
(Mennema
Belgium, Germany (Matthies 1985,
as
flowering plants
(chalk grasslands)
are
due
use
and colour as
size, shape
populations
and the
conspicuous
very
same
may also be due
to a
of herbicides.
the flower and bract colour,
to
only aspects of germination, parasitism and distribution have received attention (Gislen
1949, Oesau 1973,1975,Weber 1976, Matthews 1985,1986). This study
of M.
arvense
was
undertaken in order
increase
to
species of Pedicularis,
other Rhinanthoideae than
knowledge
our
Rhinanthus and
1977, 1979). The rarity of the species in The Netherlands
out
this
survey
in order
pollinators (bumblebees)
described. A
comparison
individuals, including
MATERIALS
on
Dutch
were
and
Netherlands)
Verdun
(France).
In 1987 the
observation
visiting populations
Nolle
near
made in populations
were
originated
plots
were
4 days in the
The effectiveness of
sites
on
from 6th
In
transfer
1986 and
In
were
1987
1987
Co.).
collected and the
carry
The behaviour of
seed
production
is
to
21
with
a
in
bud
experiments
were
on
in Switzerland
arvense
Main).
(Assen, Bovensmilde
derived from
st
The
July.
was
in the north
population
a
50
plots of
of 15
In 1986 and
x
50
of the
flowering
recorded.
were
studied
by touching
the
These bumblebees continued their
styles
caged
artificial
each.
times per
min, eight
density
cm
near
pollen
brush containing fluorescent powder
examined with
powder (population Crusch
plants
two
of M.
period
a
bumblebees
by
visiting bumblebees
the presence of fluorescent
potentials.
(Kwak
to
with different numbers of
Wertheim am
from seeds
observed for
period
Fluorescent Heffner and
Visited flowers
trips.
pollen
the bodies of the
(‘Daylight’
the
on
populations
and the number of flowers per plot per observation day
axes
M. pratense
species.
in Bovensmilde was divided into three
the
to
day, for
observed
which had
population
Bumblebee visitors
their effect
pollination
added incentive
an
rare
the
population.
Germany (ruins
1987 additional observations
of The
of
ecology
and
arvense
was
on
the floral ecology of
METHODS
In 1977 and 1978 insects
(Crusch, Unterengadin)
M.
the
to
is made of the seed-set in
one
AND
contribute
to
on
a
portable
UV
foraging
lamp
for
1977).
in order
to
pollination
determine
were
self-pollination
carried
out
on
caged,
intact flowers.
Experiment
1: self-
Experiment
2: three
day
with
an
or
cross-pollination only
or
six
self-
or
Pollination
success
was
Toul, Dieu).
Nectar
(Drummond
a
per flower
(three pollinations
determined after 3-4 weeks. In 1987 the seed
the Dutch population
small
twice per flower
cross-pollination
per
interval of approximately 5 h).
measured in
with
once, or
cross-pollinations
pocket
was
microcaps)
(Limburg)
collected from
into the
open
nectary.
refractometer (Bellingham
volumes,
and
expressed
as
a
and three French
flowers
production
by inserting
a
2
pi capillary
Concentration of the solutes
and Stanley,
percentage
was
populations (Verdun,
was
tube
estimated
Tunbridge Wells), modified for
(grams
glucose/lOOg
solution).
The
MEL AMP YRUM AR VENSE L.
method
described
155
Kwak
by
al.
et
(1985)
used
was
for
the
of
analysis
the
sugar
composition.
RESULTS
Flower
morphology
The flowers of M.
size.
arranged
are
by
two
two
coloured bracts. The influorescence is very
nectaries that
The
lip
zygomorphic flowers (20-25 mm)
Before
downwards. The upper lip forms
stamens.
The
chamber in the
only drop
galea,
=
distinct
of the
which is
senescent
Assen
23, population
10
curve
mm
The
A
very
large, nearly
6
wilted.
1987).
rather
mm
the
corolla,
visiting
less
more or
has magentaextra
floral
life
tongue is
long
a
is pressed
the lower
push
must
enclosing
the four
each other and form a
pollen
span
the bumblebees
of
the
flower
19
mm
later when the
or
is
7-1
under the ovary
placed
therefore necessary
protruding stigma
at
mm
days
it forms
mm
broad with
a
the bottom
reach
to
of about 1
1-04
+
and
long
the
(Figs
nectar
1 and
without hairs and contains four ovules. The seeds
long,
to
platform in older
longitudinally (Fig. 2). Pollen grains
opened by
are
The
insects
flattenedhood
laterally
The corolla tube is about
pistil has
and 2-3
long
mm
also
The bracts also bear
(30-3-5 mm) are opposite
positioned
or
slender
The fruit is about 10
which
less small flat landing
from the basis. The nectary is
corolla tube.
legitimately.
which varies in
yellow band,
a
spike
two-lipped (Fig. 1). The lower lip
a more or
a narrow,
of the chambers if these
out
flower becomes
{n
of stamens
pairs
two
dense
a
conspicuous.
are
their heads into the
putting
in
(Fig. 1).
attract ants
the upper one in young flowers but forms
ones.
coloured with
pink-magenta
arvense are
The flowers
2).
are
thick elaiosome.
a
Insect visitors
Insect visitors
on
M.
arvense,
(head-thorax pollination)
nectar
two
and the
also be
can
groups
nectar
foraging
for
pollen,
and sternotribic
the
distinguished:
legitimate
Long-
and
secure
nectar, foraging
way. The sides of the flower hood and the anthers
bumblebees. The
visiting
head and thorax, while the
body
the
their
introducing
leaving
the flower
and
to
a
started
be
heads,
may
length
the
bring
about
of 15
L.,
(Table 1).
mm or more
was
visible
normal
as
long
position, introducing
to
chamber. The
nectar as
same
individuals collected
pollinators.
landed
Pollen-collecting
upside-down
on
as
B. pascuorum
(calyx slips
pollen
Pollen
normal, legitimate
Scop,
as
and
the
B.
flower).
grains
robbers
short-tongued
to
fall
phase
from the
L.
were
the
stigma
sometimes
unfolding
out
5).
when
visited flower
workers,
their heads without
the
Workers of
sylvarum
In this
onto
4 and
flower;
groomed
particularly
e.g. B. terrestris
supported
the tongue and
chambers
pollen (Figs
was
their
place
to
light-yellow clumps.
stimulate the
the upper lip,
seen
in the
cross-pollinate
B. pascuorum workers
tongues, and then vibrating their wings
Sternotribic
can
receptive. Short-tongued bumblebees,
a
of the
out
self-pollination.
in the corbiculae and
were
contacted residual
bumblebees
Bombus hortorum
visited the flower in
flowers,
individuals
collecting
pressed apart by
were
pollen dropped
stigma nototribically
behave in this way
buds with
to
they
deposited
long-tongued
observed
nectar
bumblebees
medium-tongued
heads and tongues into the corolla tube to
When
groups: nototribic
two
visitors. When foraging for
robbers.
Nototribic pollinators.
head of the
divided into
were
(venter pollination)
of the
their
pollen
(see below).
bumblebees
approached
their inverted bodies
the
by grasping
M. M.
156
Fig.
I. Influorescence of
section
through
the
Melampyrumarvense;
upper
lip
Two flowers of Melampyrum
A Bombus
pascuorum
terrestris worker
on
of
arrows
Melampyrum
arvense
worker visits
showing
indicate ants
arvense,
on
holes in the corolla tube
Melampyrum
Melampyrum arvense. Fig.
arvense
7. A
extra floral nectaries.
showing protruding pistil
(arrow)
nototribically. Fig.
nectar-robbing Bombus
and
with
an
Fig.
enclosed
intact
2.
KWAK
Longitudinal
anthers.
pistil. Figs 4
6. A sternotribic
terrestris worker
visiting
on
Fig.
3.
and 5.
Bombus
Melampyrum
arvense.
the
galea
with their
opened
the
tearing
it apart
pollen
legs,
and curved their abdomen under the
chamber
by grasping
(Fig. 6). Wing
the
edge
of the
vibrations, causing
a
galea
hissing
pollen
chamber.
They
with their mandibles and
sound,
released the
pollen
MELAMPYRUM
ARVENSE
L,
157
Table 1. Bumblebee species (only workers)
populations,
arvense
arranged
and
in
their foraging positions
to
according
Melampyrum
derived
(data
lengths
tongue
from
Pekkarinen 1979)
Tongue
length
Bovensmilde 1987
1987
Nolle 1976
Crusch 1977
Crusch
(mm)
(The Netherlands)
(Germany)
(Switzerland)
Species
Species
Bombus hortorum
hortorum
Bombus
12-42
12-42
Bombus
sylvarum
7-93
Bombus
Bombus
pascuorum
7-89
7-89
Bombus
Bombus terrestris
that
7-85
7-85
Bombus lucorum
66-37
Bombus
Bombus
pratorum
77-11
N
=
nototribic,
deposited
was
S
=
at
pollen-covered
venter
from the
after
venter
N
N
N
—
}}-
N
N
o
T
N S,
S
N,
’
’
c
S
S,
r
r=
—
robbing, —=no
r
’
r
r
-
observation.
Pollination was achieved when the
inverted bumblebee. The
several flowers and
one or
»
—
venter.
of the
—
]
sternotribic,
the
N
N
—
_
—
bumblebee
transported
it
to
stigma touched the
the
groomed
pollen
the corbiculae. Flowers
visited by sternotribic pollinators often showed signs of damage, visible as brown spots
the
destruction of flower parts, caused
complete
mandibles. The bumblebees
visited the flowers
escent
stigma
and of the
stigma (population
were
seen to
Other
In the
seed
=
long
1977), but this difference is
robbing position
production.
88)
to
a
the bees sit
the
on
(Fig. 7). They
B. pratorum L.
(measured
curve to
do
Of the flowers of the Nolle
a
upperlip
not
not
(n
had
or
as
had
43)
a
a
fluor-
=
2-32).
2
mm),
B. terrestris workers
nectar
(primary robbers).
robbers).
they
the
use
neighbouring flowers
was
or
and therefore reduce
flower,
population (26 July 1977)
that
27)
significant (x
nectar.
reach the
pollinate
pistil
=
=
very long corolla tube (+ 19
reach the
used these holes (secondary
but 19-3 % of the flowers also had
had become
have
arvense
make holes in the tube just in the
for their support
L.,
and sternotribic visitors
visited flowers 25-9%
for several bumblebee species
short-tongued species
bracts
(n
too
B. lucorum
or
of the insect’s
grasping
nototribically visited flowers, 44-2% (n
Nectar robbers. Flowers of Melampyrum
which is
noto-
sternotribically
Crusch in
L.,
and
1).
differed between
transfer of fluorescent powder). Of the
fluorescent
tearing
Bombus terrestris
sternotribically (Table
pollination efficiency
The
species
the
by
78-4% had
a
hole
bitten through; thus fertilization
impossible.
Nectar
Nectar
was
present in
tration of 30% (range
were
present
in
the
a
volume of 0.26
17-36%,
ratio
n
=
pi (range
8, population
0-0-69
Assen
fructose:glucose:sucrose
=
pi,
«
=
1987).
21)
and
a
sugar
Three main
1:0-67:0-73
concen-
nectar
(population
sugars
Crusch,
20-7-1977).
Seed production
In Table 2 seed-set and
Generally
fruits
on
fruiting of open pollinated
branches
produced
more
flowers in various
populations
seeds per flower than fruits
on
is shown.
the main axis
158
M. M.
Table
2.
Numbers of flowers
populations
of Melampyrum
populations, the density
on
main axis
arvense
plot (50
per
x
and branches,
seed-set
the estimated
1987;
flower and
per
size
population
is
per
KWAK
plant in
given for natural
50 cm) is given for the artificial population Bovensmilde
Number of flowers
Seeds
per
flower
Percentage
On
main
Size
Population
On
axis
branches
14
26-9
13-3
100
29-7
16 8
Toul
300
ND
Dieu
>1000
Limburg
Verdun
28
On
1
main
axis
1
108
117
1
0-95
Seed-set
fruiting
branches
0-56
ND
56
On
per
plant
per
plant
88
71-3
5406
0-83
49-5
30-58
78-6
ND
0-75
41 4
68-76
40-73
1-98
Bovensmildc
26
24-7
290
0-57
0-92
57-4
Plot 2
103
110
1-8
0-48
ND
371
6-43*
Plot 3
107
112
20
0-49
0-63
420
6-73
Plot
•The
Fig.
8.
1
value of plot 3
Frequency
is used
(flowers)
distributions
of seeds
Melampyrum arvense populations
except in the population
Bovensmilde showed
(per
1
fewer
more
2
the
m
plants
per
area
Caged
on
flowers had
(0 02-0-05)
indicating
(Table
the
per
flower per
Dieu. Plots with
was;
metre.
not determined
main
axis and
more
in
four
bumblebee-pollinated
in the artificial
branched
(and
to
capsule
on
were
quite
population
low-density plot
flowers
per) plants producing
plots
did
(Fig. 8), and they
not
differ in
were
found
the main axis.
of fruits
very low percentage
to
rare
the
plot 3,2880 seeds). Therefore,
and
more
The number of seeds per flowerin the
3) compared
importance
branch
high plant density
plot 1,4236; plot 2,2649
branches than
a
=
(and flower) production compared
four seeds per
often in fruits
calculation; ND
1987.
resulted in
seeds per square
or
in
low seed
production
this way. Three
more
a
for
the
open
(1 -9—4-3%)
pollinated
of insect visits for seed-set.
and seed-set
flowers
per
flower
(45-8-88-2%),
thus
MELA MPYRUM
Table
AR VENSE L.
159
3. Fruit and seed production
Melampyrum
in
open-pollinated and caged flowers
in
artificial populations of
arvense
Insect-exclosure
Open-pollinated
Location
Seeds
Seeds
Number of
Percentage
Number
Percentage
flowers
fruiting
flower
flowers
fruiting
flower
Year
per
per
Assen
1986
170
88-2
1-32
211
3-8
005
Bovensmilde
1986
177
76-3
114
257
4-3
004
Bovensmilde
1987
794
45-8
0-60
574
1-9
002
Table 4.
in
Fruiting percentages and seed set
Melampyrum
caged
flowers
arvense
artificial pollinated,
in
the
Bovensmilde
population 1987
Self-pollination
1
n
Percentage fruiting
28
32
321
59-4
Seeds/flower
fruiting
In
Experiment
when the
produce
pollination
fruiting
flowers
2
seeds
had
no
=
29)
higher
took
pollination
at a
effect
of 41-4% and
(n
a
pollination
of
a
are
50
0-54
058
118
1-57
fruit-set than
three
place
pollination
two
a
artificial
one.
to
six
times
a
decreased
day. Fruiting
increased whereas cross-pollinated
the seed-set;
1 showed
Experiment
instead of self-pollinated and
fruits seemed
The age of the flower
higher pollination frequency.
on
36-8
summarized in Table 4.
cross-pollinated
resulted in
frequency
more
pollinations
were
1
x
19
45-8
0-71
50
6
x
24
47-6
0-86
1
3
x
21
57-1
Seeds/capsule
cross-pollinations
6
x
21
if flowers
x
42
3
Percentage fruiting
The results of artificial
2
X
21-4
2
n
better
1
X
1
Experiment
Experiment
Cross-pollination
of the youngest flowers
at
(n
to
the time of
=
29)
gave
a
seed per flower ratio of 0-59, whereas pollination of the oldest
resulted in
a
fruiting percentage
of 37-9% and
a
seed per flower ratio of
0-55.
Plot observations
Visitation. In the
visitors
Bovensmilde
succeed in
B.
pratorum and
entering
approximately
visitation
was
B.
one
two
terrestris visited
the flowers. On the 9th
July
visit per flower per
high (4-91-511)
only
B. hortorum and
(nototribic pollinators);
workers of
in
population
in all
bumblebee
the
were
11) (Table 5).
The flower life span
was
On
7
important
Several
influorescences but
visitation was low in all the
day (0-96-1
plots.
species
B. pascuorum workers.
they
times
did
not
plots, resulting
the
days.
13th
July
Visitation
M. M. KWAK
160
Table
(
=
Numbers of flowers and bumblebee visits
5.
9 h
in three Melampyrum
activity period)
Bovensmilde
1
July
97
9 July
13 July
154
198
day
50 cm).
21
July
317
4 91
Ml
501
Visit/fiower/day
2
per
x
(26 plants)
Flowers
Plot
flower
plots (50
1987
population
6
Plot
per
arvense
3
59
(103 plants)
Flowers
202
193
151
0-98
2-89
Visit/flower/day
230
5 61
1 60
Plot 3 (107 plants)
1-32
Visit/flower/day
Table
6.
294
174
Flowers
Fruiting percentage
221
0-96
358
1
511
and seed-set per flower
per
60
in three
day
Melampyrum arvense plots, population Bovensmilde 1987
6
21 July
1
Plot
Fruiting
Fruiting
+
77-8
86-7
78-9
480
83-3
86-7
73-7
560
1
28
1
80
1-42
0-8
1
39
1
60
1-32
0-8
Seed-set
Seed-set
Plot
13 July
9 July
July
-1-
2
Fruiting
Fruiting
+
500
714
44-4
17
78-6
64-3
50-0
118
Seed-set
Seed-set
+
6
0-79
0-79
0-56
018
0-93
0-86
0-78
012
Plot 3
Fruiting
83-3
44-4
28-6
0
Fruiting-!-
611
61
47-6
71
Seed-set
Seed-set
+
per
=
One additional
day
varies
flower lifetime
per
high
+
visitation 39-3
between
times
0-89
0-67
0-33
0
0-89
0-67
0-52
007
hand-pollinationon the
as
a
observation
day, n per
treatment
14 and 25.
low visitation
during
1
happened
6-72
maximum. The actual
times
as
a
minimum and
visitation per flower
lifespan
for
lies
somewhere between these ranges.
Seed-set and fruiting. The results
during
the
per
in
the observation
days
are
on
fruiting percentage is considered
flower
five
per
cases,
and
day,
even
then
a
a
seed-set
and
fruiting
summarized in Table 6. If
to
positive
negative
effect
be the effect of
effect
was
was
one
of the flowers that
an
additional
observed
observed
on
2
increase of
in
days.
five
If
a
at
flowered
least 7% in
hand-pollination
cases,
no
effect
difference of OT 5
MEL AMP YRUM
AR VENSE L.
seeds/flower is considered
then a
day
per
nine
positive
be the effect of
to
effect
161
was
only
one
additional
observed in three
cases
per flower
hand-pollination
and
no
effect
was
observed in
cases.
DISCUSSION
The flowers of M.
with
a
long
(workers)
were
B. terrestris,
robbers
or
tongued
B.
that
lapidarius
species
corresponds
minor.
visiting
The
visitors
some
in
the
idea that
(1955)
Rhinanthus
also
were
and
positioning
position
on
contained
and
of
their bodies
the
body
M.
pollen grains.
approximately
lower
39-2% ±1-31 (n
=
35);
M. M. Kwak
the
most
nectar
showed the
pratense
the
pistil.
has fallen off it is
attractive
larger compared
volume 0
unpublished
0-01
+
M.
data).
It is
only
may
very
have
a
to
negative
effect
on
The
pollen
sugar concentration
250),
concen-
concentration
may be
more
of the three
sugars in
equal
nectar
1974).
M. pratense has
attractive for bumblebees for both
whether the
trace
=
arvense
composition
the corolla which is bitten and
impossible
a
(n
of
the whole underside
M. pratense but the
to
l2pl
presence
sternotribic visitors
bumblebees for both
to
of
that
first be opened.
must
present (0-26 pi) with
because of its
is also
by
visiting
than
higher
vary because
can
short-
situation
bumblebees
was
attractive mixture for bumblebees (Pouvreau
The robber bumblebees
destroying
are
was
pratense in Sweden:
ratio of 1:0*26:118. M.
nectar.
flowers
arvense
galea, which
deposited
30%. The volume is
(M.
attractive than M. pratense
amounts,
under the
is
pollen
A moderate volume of nectar
nectar.
tration is
correctly
where
This
between long-tongued
occur
26%, respectively, of the pistils
as
nectar
although
the flowers.
visitors
such
as
and medium-
only long-
fluorescent powder). This may be due to the difficulties experienced
in
bumblebees
either
population,
short-tongued
of nototribic
usually closed
species,
visitors,
that
striking
division could
a
galea
is
medium-tongued
Bovensmilde
serotinus
efficiency
and
(44%
the
short-tongued
cases
need visitors
Europe. They
present and sometimes tried to visit
pollination
sternotribic visitors
but in
and
Long-
collectors. It is
pollen
were
Werth’s
to
bumblebees
were
it.
open
and B.
workers
pratorum
sternotribic
as
to
visitors
as
among the genus in
largest
long corolla tube and because
able
are
observed
bumblebees
tongued
the
are
tongue because of the
need visitors
they
R.
arvense
the seed-set of M.
not
the
calyx.
a
and
pollen
arvense
by
After the flower
flower had been robbed
or
not
(in
Rhinanthus spp. the calyx also had holes).
The
The
lifespan
of the flower is
additional effect
of
a
relatively long (7 days) compared
single
For instance, if the visitation
important.
and ifthe visitation frequency is
13-0% and
The
in
hand-pollination
high
a
frequency
open
is low
a
flower received 39-3
to
M. pratense
flowers
flower
(4 days).
less
is, therefore,
only
receives 6-7
visits, hand-pollination
visits,
is
only
2-5%, respectively.
two
experiments
on
artificial
pollination
showed
that
increasing
pollination
frequency stimulated fruiting but that after about three pollinations fruiting decreased. In
this
case
day).
the time interval between
It is therefore possible that if
two
only
pollinations
one
seed-set would increase. In Experiment 2
and four seeds per
capsule.
in the field situation. The
and
14-3)
The
occurrence
Limburg
for the main axes,
pollination
no
was
observations
populations
16-7 and 5-4 for the
highest
69 seeds
per
plant. Branching
had
a
each
had the
was
5 h
the
day, fruiting
and
made of fruits with three
per
capsule
is also
rare
highest percentages (4-8
branches, respectively).
found 10-40 seeds per plant. The lowest value found here
the
applied
were
of three and four seeds
and Dieu
(during
approximately
was
only
Matthies
six seeds
per
(1986)
plant
and
great influence on the total seed production
162
per
because
plant
flowers
more
generally produced
a
Matthies
mentioned
(1986)
density plants (112 plants
(16 plants
per
2
m
chalk
The
).
the densities
edge
of
a
production
forest.
highest
grassland
(Barreme,
attractive
and
situation
428
better
arvense was
In
were
was
Matthies
M.
The
only
was
the
the
Bovensmilde
diversity
was
population
lower in the
surrounded
visited
by
a
If
an
in the
place
make
to
which
plants
spinosa/
arvense
long
as
vegetation
was
very
in the
isolated,
other
species
also
that
are
that
species
attract
surrounded
by vineyards.
an
O.
anthophilous
agricultural
area
than in
are
present, then insects may combine several food
attractive species is present with few individuals then this
to
bumblebees
is
Vicia
were
This combination must
likely.
14
plants).
cracca,
In that habitat
Lotus corniculatus,
and Centaurea
jacea.
is
not
A lack of seed
self-sterile.
occurs
in Rhinanthus serotinus
not too
in
high
a
The
possibly
(Kwak
1910).
habitat with
and
production
auto-deposition.
and M. pratense (Heukels
it
plant
of Dianthus deltoides
case
isolated within
population
attractive
are
instance,
is
are
cereal field
distinction between plants
a
of the Limburg population (only
the absence of a mechanism for
as
of
other
many
case
for
a
mixture of forests and abandoned farmland. If other
bumblebees
by
foraging trip.
one
arvense
the
in chalk
study
in
once
on
land and had
bumblebees. The Nolle population had very few other
short-tongued
The
population
therefore possible
was
simultaneously flowering species
M.
than in
road side
a
in this
observed
presence
combination of various
found,
edges
here (Table 2). The
agricultural
populations
have taken
M.
1 and
Matthies
).
only described populations
(1986)
and
populations
(unpublished data) found that
plant species
Ononis
farm lane
population,
also isolated from
arvense
2
fertile conditions and different host
to more
cereal fields.
plot
to
plants/m
France).
of the
present. It
and
by long-
population
other
along
High-
low-density plants
compared
104
to
reproduction.
than
2 and 3
compared
found in the Dieu
was
in
not
per
plots
the
on
plant
be confirmed by the data presented
plant
vegetation.
flowering species present.
in
of other hemi-
density
bumblebees may influence the number of species and the number of indi-
to
vidual insects.
plants
of M.
population
Haute Provence,
bumblebees
the
a
the branches
on
may be the result of
plants
high
effect
in
plants
higher (412,
cannot
per
this type of
Jennersten
found for
fruiting percentage.
The field
insect’s
the flowers
of the
not too
fewer seeds
be attributed
can
The Toul
vegetations
situated in
visited
plant and
branching
and
plants,
) produced
performance
species. This conclusion
seed
per
much
which
grasslands,
highest
per
density-dependent
a
2
m
same was
were
found that the
(1986)
produced
individuals.
parasitic
here
were
seeds per flower. The
more
habitat with convenient host
good
the
M. KWAK
M.
M.
style
1979)
in
not curve
must
be due
backwards
as
to
was
and what is described for both
arvense
sufficient host
caged plants
did
will
plants,
in the presence of other
maintain its
where
the
plant species
population
surrounding
attractive for
bumblebees.
The
studied,
natural
population
in The Netherlands has maintained itself
1950. Its number ofplants varies but in 1987 only
of survival of M. pratense
Masselink
1980)
one can
14
plants
were
applied (1-6% of the seeds will result
are
expect 7-6 45-6 plants of M.
arvense
at
least since
present. Ifthe percentages
in
an
adult plant
in 1988.
ACKNOWLEDGEMENTS
The author wishes to
express
looked after
the
plants
in
her
the
gratitude
artificial
to
Drs
Ben
populations
Hoentjen (Bovensmilde), who
and
counted
seeds,
to
Yolande
MEL AMP YR UM A R VENSE L.
for the
Holthuijzen
163
composition analysis,
nectar
for the determinationof the Bombus
information
Dr J.
the
on
rarity
Andel commented
van
their contributions are
investigations
Research
the
to
Dr P. Rasmont
to
Dr C. L. Plate
J.
ter
(Gembloux, Belgium)
Borg (Wageningen)
earlier draft of the
for additional
(Leiden)
manuscript.
and Professor
Leeuwinga
Mr E.
the final English
text.
All
gratefully acknowledged.
supported
were
which
(BION),
Dr S.
species.
on
and
and Mrs J. M. Purdell-Lewis corrected
prepared the diagram
The
of the
species
is
the
by
subsidized
Advancement of Pure Research
by
Foundation for
The
Fundamental
Netherlands
Biological
for
Organization
the
(WO).
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