Flowering dynamics, nectar secretion and insect visitation of Phacelia campanularia A. Gray

Abstract

In the years 2004-2006, flowering dynamics and nectar secretion of Phacelia campanularia A. Gray flowers as well as the insect visitation rate were studied in the climatic conditions of Lublin, Poland. The flowering of phacelia started in the middle of June and lasted for 1.5 up to 2 months. Full bloom occurred between the third and fifth week of the flowering period of this taxon. For the study period, the average weight of nectar produced by 10 flowers was 75.64 mg, weight of sugars 11.31 mg, while their concentration in the nectar was 20.2%. Among the entomofauna foraging on the flowers of phacelia, honey bees were predominant, with their proportion among the pollinators accounting for 84.8%.

Full text

ACTA AGROBOTANICA
Vol. 63 (1): 29–35
2010
FLOWERING DYNAMICS, NECTAR SECRETION
AND INSECT VISITATION OF
Phacelia campanularia A. GRAY
Anna Wróblewska
Department of Botany, University of Life Sciences in Lublin,
Akademicka 15, 20-950 Lublin, Poland
email: anna.wroblewska@up.lublin.pl
Received: 3.03.2010
Abstract
In the years 2004-2006, flowering dynamics and nectar
secretion of Phacelia campanularia A. Gray flowers as well as
the insect visitation rate were studied in the climatic conditions
of Lublin, Poland.
The flowering of phacelia started in the middle of June
and lasted for 1.5 up to 2 months. Full bloom occurred between
the third and fifth week of the flowering period of this taxon.
For the study period, the average weight of nectar produced by
10 flowers was 75.64 mg, weight of sugars 11.31 mg, while
their concentration in the nectar was 20.2%. Among the ento-
mofauna foraging on the flowers of phacelia, honey bees were
predominant, with their proportion among the pollinators acco-
unting for 84.8%.
Key words: Phacelia campanularia, flowering dynamics, ne-
ctar secretion, insect visitation
INTRODUCTION
The genus Phacelia Juss. includes more than
half of all species of the family Hydrophyllaceae. Lacy
phacelia (Phacelia tanacetifolia) is encountered most
frequently in Poland, and it is grown primarily as an
excellent melliferous plant. Flowers of different phace-
lia varieties provide a nectar and pollen source for pol-
linating insects (D e m i a n o w i c z , 1953; Z i m n a ,
1959, 1960; W a r a k o m s k a , 1972; J a b ł o ń s k i
and S k o w r o n e k , 1983; W r ó b l e w s k a , 2006).
In favourable weather conditions, promoting intensi-
ve nectar secretion in flowers, monofloral honeys are
obtained from Phacelia tanacetifolia in several Euro-
pean countries (R i c c i a r d e l l i D ’ A l b o r e and
I n t o p p a , 2000; P e r s a n o O d d o et al. 2004;
S t a w i a r z , 2006; W r ó b l e w s k a et al. 2006;
Wróbl e w s k a and W a r a k o m s k a , 2009). In Ar-
gentina honeys from Ph. secunda have been obtained
(F o r c o n e et al. 2005; F o r c o n e , 2008). Honey
from Ph. tanacetifolia is colourless in liquid state,
while after crystallization it takes on a whitish colour,
sometimes with a golden tinge. It is characterized by
aromatic scent and delicate flavour (B o d n a r č u k et
al. 1993; S t a w i a r z 2006). According to R i c c i a r -
d e l l i D ’ A l b o r e and I n t o p p a (2000), monoflo-
ral honeys obtained from the nectar of this taxon are
amber coloured and have an intense scent and flavour.
The cultivated taxa of the genus Phacelia also
include Ph. campanularia, characterized by high de-
corative values. This species is recommended for rock
gardens, for borders and flowerbeds. Its flowers provi-
de both nectar and pollen, and that is why they are vis-
ited by various insects (H o w e s , 1979; M o u n t a i n
et al. 1981; W r ó b l e w s k a , 2006).
The aim of the present study was to determine
the diurnal and seasonal flowering dynamics of Phace-
lia campanularia and to estimate the nectar production
rate and sugar yield of its flowers. Moreover, the in-
tensity of foraging on its inflorescences by pollinating
insects was investigated at different times of the day.
MATERIALS AND METHODS
In the years 2004-2006, flowering dynamics and
nectar secretion of Phacelia campanularia A. Gray flo-
wers as well as the insect visitation rate were studied in
Lublin, Poland (51
o
14’ N and 22
o
34’ E).
Monitoring of the flowering pattern was carried
out every day or every second day during two growing
seasons (2004 and 2006), recording on 10 randomly
selected plants the number of open flowers per plant

Anna Wróblewska
30
on each day. These observations were started when the
first flower buds appeared and were continued until the
end of flowering. In addition, in 2006 the daily flo-
wering pattern was determined by recording, for seve-
ral days at two-hour intervals, all open flowers on 10
marked plants. These investigations were conducted at
full bloom of the species.
The rate of nectar production in flowers was
investigated using the pipette method (J a b ł o ń s k i ,
2003). Nectar was sampled during the successive gro-
wing seasons at two dates, each time from 10 flowers
in six replications. The percentage sugar content in the
nectar was determined with an Abbe refractometer.
Sugar and honey yield per 10 flowers, per plant and per
unit area of Phacelia campanularia were determined.
In order to determine the insect visitation rate
for phacelia, the number of insects visiting its flowers
at different times of the day was recorded on four plots
with an area of 1m
2
each. Monitoring was carried out
during two growing seasons, at full bloom, in favou-
rable weather conditions for insect foraging. The num-
ber of insects was recorded at two-hour intervals, from
8:00 to 20:00 hours Eastern European Time.
The obtained results on sugar weight in ne-
ctar were subjected to statistical analysis using SAS
9.2 software. The significance of differences between
means was evaluated at a significance level of α=0.05
using Tukey’s test.
RESULTS
In the conditions of Lublin, the flowering of
Phacelia campanularia lasted from 1.5 up to 2 months.
The first flowers opened in the middle of June. Full
bloom occurred between the third and fifth week of the
flowering period of this taxon, when the mean number
of flowers per plant was within the range of 23.5-33.8
in 2004 and 28.7-48.0 in 2006 (Fig. 1). High tempera-
ture and the lack of rainfall in the first and third decade
of July 2006 reduced significantly the development of
successive flower buds and, as a consequence of that,
the intensity of flowering of the plants in the second
half of this month. In both the seasons in question,
phacelia finished blooming at the turn of the first and
second decade of August (Fig. 1), but in 2005 nearly
two weeks earlier, in the last week of July. The flower
life span was, depending on weather conditions, 2-3
days. The investigations of the diurnal dynamics of
flowering showed that the number of flowers per unit
area changed throughout the day. At the full bloom sta-
ge, from 291.6 to 475.9 flowers were recorded per 1
m
2
, but their number was the lowest at 14:00 hours and
subsequently increased reaching its maximum at 20:00
hours (Fig. 2).
During the growing season, Phacelia campanu-
laria produced on the main stem from several up to
more than a dozen lateral branches which reached a
height of 38 to 59 cm. An average of 388.7 to 437.8
flowers was recorded, and they were borne in inflo-
rescences called drepanium (Fig. 3A). Depending on
plant density per unit area and the abundance of flo-
wering, the number of flowers produced per 1 m
2
of
a flower crop was from 3692.6 in 2004 to 4159.1 in
2005, averaging 3943.4.
The nectary of phacelia is located within the flo-
wer, at the base of the ovary of the pistil (Fig. 3B). It
has the shape of a disc and greenish-yellowish colour.
The process of nectar secretion in flowers starts simul-
taneously with the opening of petals and is the most
intense in the afternoon hours. The secreted nectar ac-
cumulates at the base of the corolla tube, whence it is
collected by insects.
The weight of nectar from 10 flowers and the
concentration of sugars contained in it varied both in
particular years and between study years. The highest
mean values of nectar per 10 flowers – 91.33 mg and
94.90 mg – were obtained in the first and third years
of the study. The results in the 2005 season were more
than twice lower, reaching only 40.71 mg (Table 1).
Sugar concentration in nectar was closely correlated
with nectar weight, and it ranged between 4.0 and
44.0%. Its mean values for the successive years of the
study were 9.7%, 30.3% and 20.6%, respectively. The
average weight of sugars from 10 flowers was the lo-
west in 2004 (7.57 mg), while in the next two years it
was 12.67 mg and 13.70 mg (Table 1). Sugar yield per
plant reached mean values within the range from 294.2
to 573.6 mg. From 2.79 mg to 5.45 mg of sugars could
be obtained per 1 m
2
.
Among the entomofauna foraging on the flowers
of phacelia, honey bees were by far predominant (Fig.
3CDE), with their proportion accounting for 84.8%
(Fig. 4). Their number was the lowest in the afternoon
hours (Fig. 5). Solitary bees (7.8%) and bumblebees
(4.6%) were characterized by much lower percentages
(Fig. 4). Insects visited the flowers of the studied taxon
throughout the whole day (Fig. 5).

Flowering dynamics, nectar secretion and insect visitation of Phacelia campanularia A. Gray
31
Table 1
Nectar production of Phacelia campanularia
Year
Day and
month
Weight per 10 flowers (mg)
Sugar concentration in
nectar (%)
nectar sugars
mean range mean ± SD range mean range
2004
29 June
19 July
120.00
62.67
70.0-147.5
46.0-72.0
6.84 ± 2.35
8.49 ± 1.56
4.00-10.80
6.30-10.50
5.8
13.6
4.0-8.0
12.5-14.0
mean 91.33 - 7.66 A - 9.7 -
2005
5 July
15 July
49.83
31.60
36.0-66.0
80.0-64.0
18.53 ± 2.94
6.81 ± 2.28
15.84-22.95
3.44-9.60
34.0
26.6
25.5-44.0
15.0-43.0
mean 40.71 - 12.67 B - 30.3
2006
29 June
7 July
149.20
40.57
108.0-220.0
20.0-72.0
14.20 ± 2.39
13.20 ± 3.85
11.20-16.50
7.60-19.00
9.75
31.5
7.0-11.5
26.5-38.0
mean 94.88 - 13.70 B - 20.6 -
3-year mean 75.64 - 11.31 - 20.2 -
Means followed by the same letter are not significantly different at α=0.05
Fig. 1. Flowering of Phacelia campanularia in two growing seasons

Anna Wróblewska
32
Fig. 3. Phacelia campanularia
A – Inflorescence at the start of flowering
B – Fragment of a flower with visible nectary (n) located at the base of the ovary (o)
C, D, E – Honeybees collecting nectar
364,8
343,9
308,7
291,6
323,9
398
475,9
0
100
200
300
400
500
08:00 10:00 12:00 14:00 16:00 18:00 20:00
hours
Number of flowers/ 1 m
2
Fig. 2. Diurnal dynamics of Phacelia campanularia flowering
2

Flowering dynamics, nectar secretion and insect visitation of Phacelia campanularia A. Gray
33
honeybees
84,8%
solitary bees
7,8%
bumblebees
4,6%
others
2,8%
Fig. 4. Proportions of various groups of insects foraging on Phacelia campanularia flowers
0
1
2
3
4
5
6
08:00 10:00 12:00 14:00 16:00 18:00 20:00
hours
Number of insects/ 1 m
2
honeybees
solitary bees
bumblebees
others
Fig. 5. Daily insect visitation of Phacelia campanularia flowers
DISCUSSION
In the conditions of Lublin, the flowering period
of Phacelia campanularia occurs during the summer
and lasts, depending on weather conditions, from the
middle of June until the last days of July or until the
end of the first decade of August. The number of flo-
wers per 1 m
2
changed during the season and reached
its maximum at the full bloom stage, which occurred
after 3-5 weeks from the beginning of flowering of this
species. The flowering times estimated for Ph. campa-
nularia during the three-year study period are longer
than those given by K r a u z e et al. (2004) for this
species, but also longer than the times noted for Ph.
Whitlavia, Ph. grandiflora, Ph. viscida and Ph. tana-
cetifolia (Z i m n a , 1960).
The observations of the diurnal dynamics of flo-
wering showed that the number of flowers per plant
changed throughout the day. From the morning hours,
the number of open flowers decreased with an increase
in temperature until noon, and then it increased rea-
ching the maximum value in the evening hours. During
the full flowering period, the number of Ph. campanu-
laria flowers per 1 m
2
was 3.6-4.1 thousand. Accor-
ding to W i l i a m s and C h r i s t i a n (1991), Ph.
tanacetifolia is characterized by similar abundance of
flowering, producing from 2 up to 4 thousand flowers
on such area, depending on the sowing date.
In the available literature, no information was
found on nectar production of Ph. campanularia flo-
wers and the insect visitation rates. Likewise in other
phacelia species (H o f m a n n , 1999), the nectary of
2

Anna Wróblewska
34
the studied taxon has the shape of a disc located at the
base of ovary. During its lifetime, one flower secreted
on average 7.56 mg of nectar. This value is higher than
that obtained by Z i m n a (1960), in the conditions of
Poland, for Ph. Whitlavia (6.18 mg), Ph. grandiflora
(4.76 mg), Ph viscida (2.70 mg), and Ph. tanacetifo-
lia (1.42 mg). According to F l o r i c a and I l l y é s
(1967), in the conditions of Romania, one Ph. tana-
cetifolia flower produced 0.173 mg of nectar per day.
The study average for sugar yield per one Ph. campa-
nularia flower was 1.13 mg, whereas in other phace-
lia species, studied by Z i m n a (1960), it was from
0.37 to 0.96 mg. Sugar concentration in the nectar of
Ph. campanularia changed, depending on the weather
conditions prevailing before and after nectar secretion,
and it ranged between 4.0 and 44.0%. These values are
comparable to those obtained for Ph. Whitlavia, Ph.
grandiflora, Ph viscida, and Ph. tanacetifolia, in which
the percentage sugar content in nectar was within the
range from 8.9 to 35.9 (Z i m n a , 1960).
Among the insects foraging on the flowers of
Ph. campanularia, honey bees predominated, with
their proportion reaching as much as 84.8%. They were
mostly interested in the collection of nectar. These re-
sults are similar to those quoted for Ph. tanacetifolia
in Greece (T h r a s y v o u l o u and T s i r a k o g l o u ,
1994; P e t a n i d o u , 2003). According to W i l i a m s
and C h r i s t i a n (1991), in England only 22% of ho-
ney bees and 3% of bumblebees collect pollen from
flowers of this species.
Insects foraged on the flowers of Ph. campanu-
laria throughout the whole day. In the afternoon hours,
there was observed a decline in the number of honey
bees, which could be attributable to a smaller number
of flowers per unit area which bloomed during that
time. A significant decrease in the number of honey
bees in the afternoon hours was also noted for Phacelia
tanacetifolia in Germany (W a l t h e r - H e l l w i g et
al. 2006), while in Greece the most intense foraging
on the flowers of this species was observed between
10.00 h and 17.00 h (T h r a s y v o u l o u and T s i r a -
k o g l o u , 1994).
CONCLUSIONS
1. Sugar yield of Phacelia campanularia per unit area
is closely correlated with the nectar production rate,
the abundance of flowering of its plants as well as
their density in a given area.
2. The flowers of the studied taxon were visited by va-
rious pollinating insects, among which honey bees
collecting nectar were by far predominant.
3. Phacelia campanularia can be recommended for
cultivation as an attractive ornamental species pro-
viding nectar forage for insects during the summer.
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Dynamika kwitnienia, nektarowanie i oblot
przez owady Phacelia campanularia A. Gray
Streszczenie
W latach 2004-2006 badano w warunkach Lub-
lina dynamikę kwitnienia, nektarowanie oraz inten-
sywność oblotu przez owady zapylające kwiatów Pha-
celia campanularia A. Gray.
Kwitnienie facelii rozpoczynało się w połowie
czerwca i trwało przez 1,5 do 2 miesięcy. Pełnia przy-
padała od trzeciego do piątego tygodnia kwitnienia
taksonu. Średnia z lat badań masa nektaru wytworzo-
na przez 10 kwiatów wyniosła 75.64 mg, masa cukrów
11.31 mg, a ich koncentracja w nektarze 20.2%. Spo-
śród entomofauny oblatującej kwiaty facelii domino-
wały pszczoły miodne, których udział wśród zapylaczy
osiągnął 84,8%.