Cirsium wallichii DC. (Asteraceae): a key nectar source of butterflies

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In general, both larvae and adult butterflies depend on plant resources (Kitahara et al. 2008;Nimbalkar et al. 2011). Adult butterflies forage on a wide variety of plant species for floral nectar (Courtney 1986;Raju et al. 2004). Butterflies, however, do not collect nectar extensively from all the available flowers (Kunte 2000). Thus, the diversity of the butterfly community of a region is associated with the availability of host plants (Murphy & Wilcox 1986;Kitahara et al. 2008). Also, the diversity and abundance of pollinators such as butterflies are crucial for the reproductive success of flowering plants (Mukherjee et al. 2015). Several wild plants considered as weeds serve as important nectar sources for butterflies (Mukherjee et al. 2015;Kapkoti et al. 2016). One such wild weed, Cirsium Mill. (Thistle) of the family Asteraceae has been well recognized as a nectar source of butterflies (Robertson 1928;Tooker et al. 2002;Kapkoti et al. 2016). Cirsium is a speciose genus of Asteraceae, with about 200 species distributed in Europe, Asia, North & Central America, and northern Africa (Mabberley 2008;Sahli et al. 2017). Among the species of this genus known from India, Cirsium wallichii DC. has been extensively used as a traditional medicinal plant in the Himalaya (Uniyal et al. 2011). Interestingly, owing to a lack of information on Cirsium wallichii DC. as a nectar source of butterflies, the current communication aims to address the value of Wallichii's Thistle not only as a weed, but also as a nectar source of butterflies.
The present study was conducted from May to August, 2019 in Benog Wildlife Sanctuary (30.467°N & 78.027°E), Mussoorie, Uttarakhand, India. The sanctuary is characterized by Banj Oak Quercus leucotrichophora forests, Chirpine Pinus roxburghii forests and grasslands (Champion & Seth 1968) which harbour at least 335 species of vascular plants (Kumar et al. 2012). The survey was done between 08.00h and 11.00h to record the butterfly species visiting Cirsium wallichii. We photographed representatives of each butterfly species from the area. Based on the photographs, identification of the species was carried out using Evans (1932) and Kehimkar (2016).
Cirsium wallichii grows along open and modified stream habitats in the sanctuary as well as near human settlements and agricultural lands at the peripheral area (Image 1A). Leaves are stalkless and pinnately lobed with long spines at the margin. The plant blooms from May-July. Capitula are many-flowered, solitary or clustered and borne on leafless stalks. They are 2-3.4cm J TT

J TT
across, homogamous, bisexual, discoid, and clustered in corymbose racemes (Image 1B). Florets are about 2cm long, pale-white, corolla tube long, limb five-toothed and pappus hair pale-white. Outer involucre bracts are lanceolate with spreading erect or recurved spines; inner bracts dilated, lanceolate-ovate and incurved near the apex (Image 1C). During recent field explorations in the Benog Wildlife Sanctuary, a total of 62 species and subspecies of butterflies belonging to 45 genera and five families foraging on Cirsium wallichii for nectar were documented (Table 1 and Images 2-5). The species assemblage includes Nymphalidae (35.5%), Hesperiidae (22.6%), Lycaenidae (17.7%), Pieridae (16.1%) and Papilionidae (9.7%). Among the recorded butterflies, five species such as Aporia agathon, Gonepteryx rhamni, Celaenorrhinus munda, Vanessa cardui, and Vanessa indica frequently visited the flowers for nectar while Pontia daplidice and Callerebia nirmala were recorded only once visiting the flowers. We also observed Vanessa cardui (Nymphalidae) utilizing C. wallichii as a larval host plant. During the study period, C. wallichii was the only species that attracted diverse butterfly species.
Cirsium has been studied in terms of nectar source by several workers such as Robertson (1928) who reported 14 species of Lepidoptera foraging on C. vulgare, eight species on C. altissimum and nine species each on C. discolor and C. pumilum. Thirty-three pollinators including 15 species of butterflies visiting C. verutum have been reported from the western Himalaya (Kapkoti et al. 2016). Although, it is used as a medicinal plant by the tribal people of the Himalaya (Uniyal et al. 2011), C. wallichii has never been reported as an important forage. The present communication highlights the importance of C. wallichii as a key nectar source for a large number of butterfly species though the plant is considered as a weed. The visits of several species J TT hexose-rich sugar and strong amino acid content in the florets. This characteristic of the plants belonging to the family Asteraceae has been reported by Baker & Baker (1983). As observed on Wendlandia tinctoria (Raju et al. 2011), clustered flowering of C. wallichii also have benefited the butterflies thus, reducing searching time. Thistle in the Himalaya such as C. verutum has been found as an important forage (Kapkoti et al. 2016) and it proves to be an important resource for butterflies in the Benog Wildlife Sanctuary, Mussoorie. This study indicates that there is a need for further studies to understand the role of C. wallichii in sustaining butterfly diversity at landscape level during summer season.