Chromolaena odorata (L.) King
& H.E. Robins (Asteraceae), an important nectar source for adult
butterflies
P. Vara Lakshmi 1 & A.J. Solomon
Raju 2
Department of Environmental Sciences, Andhra University,
Visakhapatnam, Andhra Pradesh 530003, India
Email: 1 varalakshmi83@gmail.com, 2 ajsraju@yahoo.com
(corresponding author)
Date of publication (online): 26 February 2011
Date of publication (print): 26 February 2011
ISSN 0974-7907 (online) | 0974-7893 (print)
Editor: K.R. Sasidharan
Manuscript details:
Ms # o2504
Received 06 July 2010
Final received 30 October 2010
Finally accepted 10 February 2011
Citation: Lakshmi, P.V. & A.J.S. Raju (2011). Chromolaena odorata (L.) King & H.E. Robins
(Asteraceae), an important nectar source for adult butterflies. Journal of Threatened Taxa 3(2): 1542-1547.
Copyright: © P. Vara Lakshmi & A.J. Solomon Raju 2011. Creative Commons
Attribution 3.0 Unported License. JoTT allows unrestricted use of this article
in any medium for non-profit purposes, reproduction and distribution by
providing adequate credit to the authors and the source of publication.
Abstract: Chromolaena odorata is a seasonal weed and grows like a cultivated crop. It flowers during October-December. The
floral characteristics such as white to purple colour of florets, short-tubed
narrow corolla with deep seated nectar, the morning anthesis and the
flat-topped head inflorescence providing a standing platform are important
attractants for visitation by butterflies. The florets attract
butterflies of five families and sphingid hawk moths. Among the butterflies, nymphalids are diverse and visit the
florets consistently; their visits effect pollination. The diurnal hawk moths, Macroglossum gyrans and Cephonodes hylas also visit the florets during dawn and dusk hours for
nectar, and effect pollination. Therefore, C. odorata, being an exotic is an important nectar source for adult
butterflies.
Keywords: Butterflies, Chromolaena odorata, nectar, psychophily.
This article
is part of the peer-reviewed Proceedings of the 3rd Asian
Lepidoptera Conservation Symposium (3ALCS-2010) jointly organized by the IUCN
SSC South Asian Invertebrate Specialist Group (SAsISG); Department of
Zoology, Bharathiar University; Zoo Outreach Organisation and Wildlife
Information Liaison Development, held from 25 to 29 October 2010 at Coimbatore,
Tamil Nadu, India. http://www.zooreach.org/3alcs2010.html
For figures, images,
tables -- click here
Chromolaena odorata is a perennial weed in
many parts of the world from sea level to over 1,000m in elevation (Binggeli
1999). It was introduced into
India from tropical America during the Second World War and since then it has spread
widely and has become a dominant weed of wastelands, roadsides and other
exposed areas (Kushwaha et al. 1981). Disturbance is a pre-requisite for the colonization of
an area by this plant and once colonized, it competes aggressively with herbs,
grasses, and shrubs in open areas. It is not shade-tolerant and does not grow under a closed forest stand
(Francis 2001). It possesses an
underground organ which ensures its survival in case of fire, drought or
mechanical damage through coppicing (Schmidt & Schilling 2000). Its reproduction is exclusively by
seeds (Coleman 1989). Sexual
reproduction starts when the plant is one-year old and this observation agrees
with Schmidt & Schilling (2000) who reported similarly. In the present study sites, this weed
occurs in open, sunny areas of forest margins and open gaps in the forest at an
elevation of over 700m. The
regular disturbance in the forest due to various human activities facilitates
colonization of exposed areas by this plant. C. odorata grows like a crop during the active growth period and suppresses
the growth of native low ground herbaceous flora. This paper describes the importance of C. odorata as a nectar source for
adult butterflies.
Materials and Methods
Chromolaena odorata occurring at the
Seshachalam Hills of southern Eastern Ghats of Andhra Pradesh was used for the
study during the summer season of 2009. Twenty-five tagged mature buds were followed for recording the time of
anthesis and anther dehiscence. The details of flower morphology such as flower sex, shape, size,
colour, odour, sepals, petals, stamens and ovary were described. Regular observations were made on the
butterflies visiting the flowers for forage. They were observed for their foraging behaviour such as mode
of approach, landing, probing behaviour for nectar collection, contact with
essential organs to result in pollination, inter-plant foraging activity in
terms of cross-pollination, etc. The foraging visits of each butterfly species for the entire day on the
selected number of flowering heads were recorded to know the relative
percentage of visits of each butterfly family. Three to five specimens of each butterfly species collected
at different times of the day were brought to the laboratory for examining
their proboscis under a microscope for the presence of pollen grains in order
to assess their role in pollen transfer and pollination.
Results
Floral biology: The plant is a free
standing shrub and grows up to 1m. It is maintained by a system of abundant, yellowish, fine lateral roots. The opposite, three-nerved leaves are
ovate-lanceolate, usually with a dentate margin and a long pointed tip. Seed
germination starts in May-June and active growth occurs during June-October. The plant possesses underground organs
which ensure its survival during drought or mechanical damage or in case of
fire. Flowering does not occur in the first year but it occurs in the
consecutive years during October-December. The inflorescences consist of corymbs of cylindrical heads;
they arise at the terminal part of the branches (Image 1a). A cylindrical head consists of 21 to 28
tubular florets per head (Image 1b,c). The florets open during 0600-0800 hr
(Image 1d-g). They are very small,
white to light purple, bisexual, and zygomorphic. The calyx is reduced to pappus and represented by
hairs. The corolla is tubular with
five teeth at the tip. The stamens are five, epipetalous, arise from the base
of the corolla, filaments are free but anthers are united representing
syngenesious condition. The
anthers are dithecous, have their connective prolonged into hood and their
bases produce hairy outgrowths, which in turn form a protective envelope for
the nectary. The pollen grains are
very small, round, ornamented, 196 ± 14.6 per anther and the total pollen output
per floret is 980 (Image 1h). The
narrow anthers form a hollow space and pollen is liberated into this
space. The ovary is bicarpellary
and syncarpous, unilocular with a single basal ovule (Image 1i,j). The style is surrounded by the nectary
at the base and it is forked into two parts. The receptive surfaces of the stylar branches stay in the
closed state and as they grow through the hollow space brush out the pollen
liberated in the hollow space. Further, the style stretches out beyond the anthers, spreads out its
branches to receive pollen. The
nectar is secreted in traces only; for this reason nectar analysis was not
carried out. The florets remain in
place for about 3-4 days. The fruits are small and one-seeded. The seeds are dry, light and 4mm long brownish gray to black
achene with a small hook and tipped with pale brown 5-6 mm long pappus (Image
1k).
Foraging activity of butterflies and
hawkmoths: The florets were visited during day time by butterflies and
hawkmoths for nectar collection. The
butterflies included 23 species representing the families: Papilionidae,
Pieridae, Nymphalidae, Lycaenidae and Hesperiidae (Table 1). The Papilionidae and Pieridae each was
represented by three species, Nymphalidae by 14 species, Lycaenidae by two species
and Hesperiidae by one species (Fig. 1). The papilionids were Pachliopta hector (Image 1l), Papilio polytes (Image 1m) and P. demoleus. The pierids were Catopsilia pyranthe (Image 2g), Anaphaeis aurota and Delias eucharis (Image 2f). The nymphalids
were Danaus genutia (Image 2c), D. chrysippus (Image 2d), Junonia lemonias (Image 1p), Precis iphita, Junonia hierta, Euploea core (Image 2a), Ariadne ariadne (Image 1o), Acraea violae (Image 1n), Phalanta phalantha (Image 2b), Ypthima asterope (Image 2i), Melanitis leda,
Tirumala limniace (Image 2e), Parantica aglea and Neptis hylas. The lycaenids were Everes lacturnus and Tarucus nara (Image 2h). The hesperid was Borbo cinnara of these, the individuals
of nymphalid butterflies foraging at the florets were found to be more than
those of other families throughout the flowering season (Fig. 1). The data collected on the foraging
visits of butterflies of each family showed that nymphalids made 61%,
papilionids 17%, pierids 11%, lycaenids 8% and hesperiids 3% of the total
visits (Fig. 2). The cylindrical
heads equipped with a cluster of florets provide a convenient landing place for
butterflies and also this arrangement enables them to probe several flowers in
each visit in succession for nectar before their departure. The flowering heads borne terminally
stand out prominently and the butterflies were found to be attracted to them
even from a long distance. A
sample of 3-5 specimens of all butterfly species was used to examine the pollen
carrying capacity of their proboscises. The results indicated that the proboscises invariably contained pollen
grains ranging from 15-35 in papilionids, 14-23 in pierids, 29-189 in
nymphalids, 8-17 in lycaenids and 9-21 in hesperiids. All these butterflies stretched out their proboscises to
reach the floret base to access nectar; while doing so the proboscis invariably
contacts the stylar surfaces and hence effects pollination. They frequently moved between
individual plants of C. odorata which has patchy distribution along the forest margins and in the
open gaps of the forest interior; this inter-plant foraging activity within the
patch and between patches situated nearby and far away promotes cross
pollination. The study showed that
nymphalids play an important role in the pollination of C. odorata. The diurnal hawk moths included Macroglossum gyrans (Image 2j) and Cephonodes hylas (Image 2k). These hawk moths showed intense foraging
activity during dawn hours when the florets offer fresh nectar and reduced
activity during dusk hours when the florets offer only the leftover nectar
which is not fresh; they rarely foraged during daytime. They hovered at the floret heads,
inserted the proboscis, and collected nectar quickly from as many florets from
several flowering heads in quick succession. Their proboscis gained contact with the stylar surfaces of
each floret they visited and this contact results in pollination.
Discussion
The floral characteristics of C. odorata such as white to purple
colour of florets, short-tubed narrow corolla with deep seated nectar, the
flat-topped head inflorescence providing a landing platform and morning
anthesis suggest that the plant is psychophilous (Faegri & van der Pijl
1979). Galetto & Bernardello
(2003) reported that hexose nectars are characteristic of Asteraceae. Baker & Baker (1983) also stated
that hexose sugars dominate in the nectars of Asteraceae and the nectars are
also relatively strong in amino acids to compensate for the low sucrose-hexose
ratio in the members of this family which attract butterflies. Since C. odorata is a member of Asteraceae,
hexose-rich sugars and high amino acid concentration could be expected in the
nectar. The retention of florets
for extended periods may enhance the attractiveness of flowering heads to
visiting butterflies. C. odorata with these floral structural and functional characteristics
attract butterflies and hawk moths. The butterflies of all families collect nectar from the flowering heads
as soon as the florets are open and in doing so effect both self- and
cross-pollination. Since the
florets secrete traces of nectar, the butterflies in quest of nectar visit as
many florets and flowering heads as possible in a single foraging visit, this
foraging behaviour promotes cross-pollination. The patchy distribution of the plant with numerous flowering
heads facilitates frequent movement of butterflies between different
individuals and such movements promote cross-pollination. Since the florets are short-tubed, the
butterflies with any length of proboscis collect nectar without any
difficulty. The florets borne in
cylindrical heads collectively offer considerable quantities of nectar and are
energetically profitable for butterflies and such an arrangement reduces search
and flight time. The proboscises
of butterflies carry pollen and the quantity recorded may be related to the
length of the proboscis and the contact extent between the proboscis and the
dehisced anthers. Among the
butterflies, Nymphalids frequent the flowers consistently throughout the season
in individual numbers and species, and hence play a prime role in the
pollination, more than other butterflies. In another exotic species, Tridax procumbens, an Asteraceae member,
danaid and pierid butterflies have been shown to be the main pollinators by
Balasubramanian (1989). Therefore,
psychophily is adaptive and advantageous for the plant to maximize pollination
with specialized florets and nectarivory of butterflies.
The diurnal hawk moths, Macroglossum gyrans and Cephonodes hylas also visit C. odorata flowering heads during
dawn and dusk hours. The dawn
foraging activity is energetically profitable for them while the foraging at
dusk period may not be as profitable as the florets by that time are likely to
be emptied of nectar by butterflies and other insects during the day. They collect nectar on clear sunny and
rainy days and utilize this floral source until exhausted. Balasubramanian (1989) reported that
hawk moths visit the florets of Tridax procumbens during rainy weather when most butterflies take shelter among
foliage in nearby bushes. In the present study, it is found that the
butterflies do not visit C. odorata on rainy days and hence they effect pollination only on clear
sunny days. The study shows that C. odorata being an exotic weed is psychophilous and its
prevalence in the forest areas is a potential source of nectar for butterflies
for a period of three months. Although it is a menace due to its prevalence and suppressive activity
on the growth of certain native low ground herbs, its flowers are most
attractive to butterflies throughout its distribution range and act as a
provisioning post for the butterflies. Its abundant growth everywhere in the
tropics might also be depriving the pollination services to native flora, which
are butterfly pollinated.
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