Reproductive Success and Insect Visitation in Wild Roses (Rosa spp.) –
Preliminary Results from 2004
Victoria J. MacPhail and Peter G. Kevan
University of Guelph, Dept. of Environmental Biology, Guelph, Ontario N1G 2W1
Canada
Keywords: hips, fruit set, pollination, reproductive systems, insect observations,
pollinators, Hymenoptera, Syrphidae
Abstract
The hips of wild roses (Rosa spp.) contain many healthful compounds such as
vitamins and antioxidants. There is great interest in commercial cultivation but before
this can occur, questions regarding plant reproduction and pollinators need to be
addressed. Preliminary trials from 2004 investigated the pollination biology of five
native or naturalized roses in Ontario and Prince Edward Island, Canada. The
reproductive systems of Rosa blanda, R. canina, R. cinnamomea, R. multiflora and R.
virginiana were investigated through pollination trials, and the potential pollinators of
these species were surveyed. Hip and seed production by agamospermy, automatic
autogamy, geitonogamy, xenogamy, emasculation control and open-pollination were
tested for each species. Reproductive success, the number of hips set over the number
of flowers, was calculated for each treatment. Rosa blanda and R. multiflora
reproduced by open-pollination, geitonogamy and xenogamy; R. canina and R.
virginiana were also autogamous. Both R. multiflora and R. virginiana set one hip
asexually (through agamospermy). Interestingly, R. cinnamomea did not set fruit in
any treatment or site. Pollinator activity was quantified twice in the season for each
species. The number, type (most were hover flies (Syrphidae) or bees (Hymenoptera)),
and behavior of insect visitors, as well as the time spent foraging, was recorded during
10 minute intervals on an hourly basis. Insect visitation rates were highest between
0900 and 1200, and foraging rates peaked sharply at 0900, indicating the probable
period when the most pollen was available. Identified bee genera included Andrena,
Apis, Augochlorella, Bombus, Calliposis, Ceratina, Halictus, Hylaeus, Lassioglossum,
and Xylocopa.
INTRODUCTION
Wild roses (Rosa spp.) have the potential to become a new crop with economic
benefits to farmers and processors. The “fruit” of roses, known as hips, contain many
healthful compounds like vitamins, minerals and antioxidants, which are advocated for
the prevention of heart disease, stroke, and cancer (Daels-Rakotoarison et al., 2002;
Zheng and Wang, 2003; Uggla, 2004). As demand for these compounds increases,
pharmaceutical companies, preserve makers, and wineries are interested in acquiring
adequate local sources, but first agronomic information, including that on pollination and
fruit set, must be obtained.
Roses are hardy, perennial shrubs that can grow in almost all habitats, making
them an ideal crop plant (MacPhail, 2004). Wild roses have open ‘dish’ to ‘bowl’ shaped,
usually single, hermaphroditic flowers, which yield an edible hip (a fleshy or pulpy
receptacle) that contains numerous achenes (one-seeded fruits) (Faegri and van der Pijl,
1979; Kevan et al., 1990). Rose hips are used in making tea, jam, jelly, marmalade, puree,
wine, and fruit juice (Uggla and Nybom, 1999). They are also eaten by many birds and
mammals, often as emergency food in winter (Schneider, 1995). The medicinal use of
rose hips is not a new occurrence. They have been used for treating fatigue, eye diseases,
heart diseases, insomnia, respiratory diseases, stomach troubles (e.g. diarrhea, dysentry),
menstrual cramps, dry skin, inflammation, and for preventing kidney stones and scurvy
(Cutler, 2003). Recently, anti-inflammatory, antioxidant, and antimutagenic properties
have been shown (Daels-Rakotoarison et al., 2002; Uggla, 2004). Some species’ hips may
Proc. IVth IS on Rose Research and Cultivation
Ed. H.B. Pemberton
Acta Hort. 751, ISHS 2007
381
contain 20-25 times more vitamin C, by weight, than oranges do (Roland, 1998), and may
have an even greater antioxidant capacity than blueberries, cranberries, and other fruits
(Zheng and Wang, 2003; Uggla, 2004).
Some flowering plants produce fruit and seed using their own pollen, but others
require pollen from a different plant, or no pollen at all (Richards, 1997). Knowledge of
rose reproduction is needed to manage the plants for crop production. However,
pollination in Rosa has not been well studied experimentally (Kevan et al., 1990). It was
once believed that automatic autogamy (self-pollination) occurred in all roses (e.g. Knuth,
1908), but many Rosa species do not set fruit by self-pollination. Low fruit sets from selfpollination can be the result of self-incompatibility (Jičínská, 1975, 1976; Stougaard,
1983; Cole and Melton, 1986; Ueda et al., 1996). This has now been confirmed in several
species, including R. multiflora and R. rugosa (Jičínská, 1976; Stougaard, 1983; Ueda et
al., 1996) (but see self-compatibility reported for R. multiflora by Wulff (1952) and
Kordes (1955) (both cited in Stougaard, 1983)). Many self-compatible species have
increased hip set with cross-pollination (Ueda and Akimoto, 2001). Rosa setigera is the
only known dioecious rose (Kevan et al., 1990).
Although agamospermy (the production of fruit without fertilization) is common
in many rosaceous genera, such as Rubus, Sorbus, and Potentialla (Richards, 1997),
researchers are in disagreement as to its’ presence in Rosa (Werlemark, 2003). However,
several species, especially those in the Caninae section (e.g. R. canina), are suspected of
having heterogametic or irregular meiosis along with agamospermy (Cole and Melton,
1986; Kevan et al., 1990; Werlemark, 2003).
Roses are insect pollinated (Stougaard, 1983; Kevan et al., 1990). A large variety
of beetles, flies, bees and other insects visit rose flowers. Bumble bees, carpenter bees,
honeybees, and hover flies are the most common. Other examples include thrips, chafers,
and earwigs, which are considered as destructive visitors, and crab spiders, which ambush
flower-visiting insects (Stougaard, 1983; Yeboah Gyan and Woodell, 1987; Kevan et al.,
1990; Kevan, 2003).
Plant breeding programs for rose hip production have been initiated in many
countries, including Czechoslovakia, Bulgaria, Germany, Russia, and Sweden (Jičínská,
1976; Uggla and Nybom, 1999; Uggla, 2004) and are currently being investigated in
Canada by the Atlantic Canada Network on Bioactive Compounds (MacPhail, 2004). The
purpose of this study was to investigate the reproductive systems of Rosa blanda, R.
canina, R. cinnamomea, R. multiflora and R. virginiana through pollination trials, and to
survey the potential pollinators of each species through insect observation trials and
collections.
MATERIALS AND METHODS
Fifteen sites from southern Ontario, Canada (owned by the Royal Botanical
Gardens and the Guelph Arboretum) containing Rosa blanda (4 sites), R. canina (5 sites),
and R. multiflora (6 sites), and six sites from central Prince Edward Island, Canada
(private landowners) containing R. cinnamomea (2 sites) and R. virginiana (4 sites), were
used in this study. A site was defined as either a single bush with all ramets coming from a
single base (for R. multiflora) or a localized patch of roses with many individual ramets
growing in close proximity to each other (for all other species). It was assumed that all the
ramets within a site were genetically similar to each other (e.g. derived from vegetative
reproduction) (i.e. are all part of one plant), and different from all other sites. All sites
were wild (un-managed) populations whose origins are unknown.
Reproductive Systems
Six treatments were replicated five times at R. blanda, R. canina, and R. multiflora
sites and eight times at R. cinnamomea and R. virginiana ones. Therefore a total of 20, 25,
30, 16, or 32 flowers were used in each treatment, for each species respectively, using
standard methods. These treatments included 1) agamospermy (no pollination - stigmas,
stamens removed; bagged), 2) automatic autogamy (self-pollination - no external
382
manipulation; pollen from same flower; bagged), 3) geitonogamy (self-pollination external manipulation; pollen from different flower, same plant; stamens removed;
bagged), 4) xenogamy (cross-pollination - external manipulation; pollen from different
site of the same species; stamens removed; bagged), 5) emasculation control (control –
stamens removed; un-bagged), and 6) open-pollination (control – no manipulation)
(Kevan et al., 1990; Dafni, 1992; Ueda and Akimoto, 2001; Dafni et al., 2005).
Flowers at the “late-pink” bud stage (petals just starting to show through sepals)
were selected (i.e. before anthesis and anther dehiscence) for use in each of the above
treatments. Hand-pollinations of receptive stigmas were carried out (where applicable)
using small numbers of freshly collected individual anthers (approx. 30 - 60% of total
number per donor flower) on June 22-24 (R. blanda, R. canina (3 sites), R. multiflora),
July 3 (R. canina (2 sites)), July 13 (R. cinnamomea), and July 21-22 (R. virginiana),
2004. Donor flowers were un-bagged, first day flowers, as this is the stage where the most
pollen appeared to be available. Rosa blanda, R. canina, and R. multiflora were pollinated
during their second day of bloom, while R. cinnammomea and R. virginiana were
pollinated during their first day, as this is the time of greatest stigma receptivity. All bags
were removed about 1 to 1 ½ weeks after pollination, well after the period of stigma
receptivity ended. In early fall, 2 ½ months after pollination, any hips that had formed
were collected and frozen at approximately -15 °C. They were then measured, weighed,
dissected, and the achenes counted and weighed (data not presented here). Reproductive
success was calculated as the number of hips formed per total number of flowers tested.
After finding no significant differences between sites for each treatment, data were
pooled, and each species was evaluated to determine its’ method(s) of reproduction.
Insect Observations
Insect observation trials were carried out by observing a known number of flowers
for ten minutes on an hourly basis from 0800 to 1600 in June, 2004 in Ontario, and 0800
to 1500h in July, 2004 in Prince Edward Island (period of most pollinator activity) (Kevan
et al., 1990; personal observation). Thirteen sites (2 R. blanda, 4 R. canina, 2 R.
cinnamomea, 2 R. multiflora and 3 R. virginiana) were observed twice and information
gathered on the number of observed flowers and insects, the type, behaviour and foraging
time of flower visitors, and environmental conditions (Kevan et al., 1990; Kearns and
Inouye, 1993; Dafni et al., 2005). Observed insects were fitted into one of seven groups:
honeybees, bumble bees and large carpenter bees, hover flies, other flies, other bees,
beetles, unknown/uncertain insect types, and other insects (including moths, grasshopperand worm- like organisms, aphids and ladybugs). The average visitation rate (total
number of visits/total number of flowers/total number of sites), average foraging rate
(total seconds spent foraging/total number of flowers/total number of sites), and overall
visitation rate (total number of visits/total number of flowers/site over 2 days) were then
calculated for each period, making no distinction between floral visitor and true
pollinator. Representative visitors were also collected using ethyl acetate fumes and are
being identified.
RESULTS AND DISCUSSION
Reproductive Systems
There were no significant differences in reproductive success between sites within
species for each treatment (Kruskal-Wallis, p>0.05), allowing data to be pooled (Fig. 1).
Rosa blanda and R. multiflora were geitonogamous and xenogamous, (i.e. selfincompatible within flowers but not within the same plant, and predominantly outcrossing), while Rosa canina and R. virginiana were automatically autogamous as well as
geitonogamous and xenogamous (i.e. self-compatible and out-crossing). The openpollination and emasculation control treatments resulted in hip set in these four species,
and R. multiflora and R. virginiana each had one hip set through agamospermy. Rosa
cinnamomea did not set fruit in any treatments.
383
Ueda and Akimoto (2001) found R. blanda to have a 5% selfed- (autogamous)
fruit set, and R. virginiana to have 90% selfed-fruit set, whereas this study found 5% for
R. blanda and 19% for R. virginiana. Jičínská (1975, 1976) found R. canina to have a
82.2% and 83.2% successful fruit set in autogamy, 50% set in geitonogamy, 37.8% in
xenogamy, and 81.4% in open-pollinated flowers, while this study had 48%, 28%, 72%
and 72%, respectively. Both Ueda and Akimoto (2001), Jičínská (1976), and this study
found R. multiflora to have 0% automatic selfed-fruit set. Stougaard (1983) tested
different clones of R. multiflora and found autogamy rates ranging from 0.0 to 1.0%, and
xenogamy rates from 71.4 to 92.5% (40% in this study).
The emasculation control treatment looked for effects of emasculation on hip set
and development; however, since insects generally only forage on intact rose flowers
(personal observation), pollination may not have occurred, causing the low numbers of
hips seen. Rosa multiflora had a relatively high 17% hip set in this treatment, but it is
possible that insects transferred pollen to the test stigmas while foraging on the numerous
small, neighbouring, intact flowers. Rosa virginiana also had a similar hip set in the
emasculation treatment (16%), although the flowers in its’ inflorescences are similar to
those of R. blanda and R. canina, which only had 5% and 4% set respectively, suggesting
an unknown factor was involved.
Rosa cinnamomea did not set fruit in any of the treatments or sites. Roland (1998)
and MacPhail (2004) stated that R. cinnamomea does not form any fruit, possibly due to a
lack of pollinators and/or self-incompatibility. Since hand pollinations did not result in
hips, it is unlikely that pollinators are the issue. The origin of the patches tested is
unknown, and so it is possible that they are clones of each other (e.g. having been
originally propagated and distributed by humans); therefore, if they are self-incompatible,
even “cross-pollination” would in fact be a form of incompatible self-pollination.
Although Ueda and Akimoto (2001) and Jičínská (1976) found 25% and 8.5% selfed-fruit
set, respectively, for R. cinnamomea, it is possible that the naturalized versions of R.
cinnamomea tested in this study have different, non-phenotypic features than their native
counterparts growing in Eurasia, causing the differing results. Additional Canadian sites
need to be evaluated before any firm conclusions can be made.
Insect Observations
Thirteen sites (five species) were observed twice during the flowering period.
Several sites did not have any visitors at certain time periods, although at least 77% of the
sites had visitors from 0900-1400h (up from 62% at 0800 and 1500, and 44% at 1600).
When all of the visitation data were pooled and adjusted for varying flower numbers, the
greatest average visitation rate (total number of visits/total number of flowers/total
number of sites) was observed at 1100h with 1.64 visits/flower/site over the 10 minutes
(Fig. 2A). It was noted that bees, especially honeybees, were more active in the mid-late
morning periods, which would translate into a greater visitation rate, not only because
there are more insects foraging, but because bees often make quick visits to many flowers
over a period of time, while hover flies visit and spend more time at fewer flowers in the
same time period (data not presented here). The greatest average foraging rate (total
seconds spent foraging on the flower/total number of flowers/total number of sites) was
observed at 0900h, with an average visit lasting 189.64 seconds/flower/site (Fig. 2B).
This sharp peak in foraging rate probably indicates when the anthers dehisced (i.e. when
the most pollen was available). After this point, much of the pollen could have been
removed, so insects would spend less time at each flower collecting pollen and more time
searching for other more bountiful flowers. There were no significant differences between
sites in the total number of insect visits/site, even after they were adjusted for the number
of flowers being observed (K-W, p=0.107) (Fig. 3).
Observed insects were fitted into one of seven groups, with an eight grouping
being a place holder for periods with no recorded visitors. When all observations are
considered together, the other bees grouping contained the most visits (459), followed by
hover flies (268), honeybees (177), bumble bees & large carpenter bees (136), other flies
384
(92), (no visitors) (62), unknown/uncertain insect types (47), other insects (44), and
beetles (32). This makes bees and hover flies more valuable as pollinators since there is a
greater chance of pollen being dispersed to several different flowers on one foraging trip,
especially compared to other flies and insects that do not forage as actively on pollen or
are often just resting on the flowers.
Representatives of most floral visitors were also collected during the summer and
are currently being identified. Thus far, identified bees from the 2004 field season include
Andrena (Andrena) thaspii, Andrena (Euandrena) geranii, Andrena (Melandrena) vicina,
Andrena (Plastandrena) crataegi, Andrena (Simandrena) wheeler, Andrena
(Trachandrena) miranda, Apis mellifera, Augochlorella aurata, Bombus (Cullumanobombus) rufocinctus, Bombus (Pyrobombus) bimaculatus, Bombus (Pyrobombus)
impatiens, Bombus (Pyrobombus) ternarius, Calliposis (Calliopsis) andreniformis,
Ceratina (Zadontomerus) calcarata or dupla, Hylaeus spp., Lasioglossum (Dialictus)
cressonii, Lasioglossum (Dialictus) laevissimum, Lasioglossum (Dialictus) near
laevissimum, Lasioglossum (Evylaeus) cinctipes, Lasioglossum (Lasioglossum) zonulum,
and Xylocopa (Xylocopoides) virginica.
CONCLUSIONS
Species in the genus Rosa were found to reproduce using different methods and to
host a variety of insect visitors. Rosa blanda and R. multiflora were found to reproduce
using open-pollination, geitonogamy and xenogamy, while R. canina and R. virginiana
can utilize autogamy, open-pollination, geitonogamy and xenogamy, and R. cinnamomea
does not appear to set hips. Both R. multiflora and R. virginiana produced one hip through
asexual means. If any of these species are to be grown on a large scale for their hips, it
must be kept in mind that R. blanda and R. multiflora will require external pollination, by
hand or through insect visits, for large amounts of fruit to be produced, although R.
canina and R. virginiana would also benefit. It was suggested that R. cinnamomea is selfincompatible, and that plants in both sites may be genetically identical. Due to the lack of
hip production, it would not be a good crop candidate.
Insect visitation rates were highest in mid-morning, especially between 0900 and
1200 when the majority of bees were out foraging, and were not significantly different
between sites. Foraging rates sharply peaked at 0900, which is thought to represent when
the most pollen was available. The majority of insect visitors were either bees
(Hymenoptera) or hover flies (Syrphidae), which are potentially good pollinators since
they make frequent visits to many flowers, although beetles and other insects were also
occasionally noted. Identified bee genera included Apis, Augochlorella, Bombus,
Calliposis, Ceratina, Halictus, Hylaeus, Lassioglossum, and Xylocopa. Increased rose
crop pollination could be achieved by introducing managed bees (e.g. honeybees) and by
increasing native bee populations by providing unmanaged land (e.g. hedgerows, old
fields) nearby for nesting. Since roses do not produce nectar, suitable nectar-producing
plants should also be included into the site plan. Further work on this project is currently
underway by the authors.
ACKNOWLEDGMENTS
Thanks to the Atlantic Canada Innovation Fund and the Atlantic Canada Network
on Bioactive Compounds for financial and research assistance, to John S. Ascher and Sam
Droege for bee identification, to James R. Kemp at the University of Prince Edward
Island for lab space and discussions, and to Colleen Fuss for help in the field.
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386
Figurese
0.8
Reproductive Success
(# hips/# flowers)
.7
.72
.7
.73
.72
Agamospermy
Automatic Autogamy
Geitonogamy
Xenogamy
Emasculation control
Open-pollination
.66
.59
0.6
.48
.4
0.4
.34
.28
0.2
.05
0.0
.17
.15
.05
.05
0
0
R. blanda
.16
.07
.03
0
R. canina
.19
R. multiflora
.03
R. virginiana
2.0
A
1.5
1.0
0.5
0.0
800
1000
1200
Time of day
1400
1600
Average foraging rate
(seconds/flower/site)
Average visitation rate
(visits/flower/site)
Fig. 1. Pooled reproductive success (#hips formed/#flowers tested) for agamospermy,
automatic autogamy, geitonogamy, xenogamy, emasculation control and openpollination treatments for Rosa blanda (5 flowers/trt/site, 4 sites in Ontario,
Canada), R. canina (5 flowers/trt/site, 5 sites in Ontario, Canada), R. multiflora (5
flowers/trt/site, 6 sites in Ontario, Canada), and R. virginiana (8 flowers/trt/site, 4
sites in Prince Edward Island, Canada) in 2004. Rosa cinnamomea (8
flowers/trt/site, 2 sites in Prince Edward Island, Canada) is not shown as it had
zero reproductive success in all treatments.
200
B
150
100
50
0
800
1000
1200
1400
1600
Time of Day
Fig. 2. Average visitation rates (visits/flower/site) (A) and average foraging rates
(seconds/flower/site) (B) for all observed insects at each time period in Ontario
and Prince Edward Island, Canada in 2004. Data has been pooled from all
observations of Rosa blanda (2 sites), R. canina (5 sites), R. cinnamomea (2 sites),
R. multiflora (2 sites), and R. virginiana (3 sites), and adjusted for varying
numbers of flowers at each observation time. No distinction was made between
insect types. Observations were carried out on fine-weather days in June, 2004
from 0800 to 1600h for all sites except R. cinnamomea and R. virginiana, which
ended at 1500h and were carried out in July, 2004.
387
Overall visitation rate
(total # insect
visits/total #
flowers/site)
4
3
2
1
0
5
7
R.
blanda
2
3 14 15 16 17 9 12 18 20 21
R. canina
R. cin- R.
namo- multmea
iflora
R.
virginiana
Site #
Fig. 3. Overall visitation rate (total number of insect visits/total number of flowers/site),
incorporating two observation days per site in 2004. Five different species were
examined: R. blanda (sites 5, 7), R. canina (sites 2, 3, 14, 15), R. cinnamomea
(sites 16, 17), R. multiflora (sites 9, 12), and R. virginiana (sites 18, 20, 21). Data
was pooled from all time periods, with no distinction made between insect types.
Observations were carried out from 0800 to 1600h for R. blanda, R. canina, and R.
multiflora in Ontario, Canada, and from 0800 to 1500h for R. cinnamomea and R.
virginiana in Prince Edward Island, Canada.
388