Taiwania, 58(3): 163‒170, 2013 DOI: 10.6165/tai.2013.58.163 RESEARCH ARTICLE Carpenter Bees and the Orchid of a Princess: Natural Pollination of Sirindhornia monophylla in Thailand Kanok-orn Srimuang(1*), Hans Bänziger(2), Henrik Æ. Pedersen(3) and Santi Watthana(4) 1. School of Agriculture and Natural Resources, University of Phayao, Phayao Province 56000, Thailand. 2. Department of Entomology and Plant Pathology, Faculty of Agriculture, Chiang Mai University, Chiang Mai 50200, Thailand. 3. Botanical Garden, Natural History Museum of Denmark, University of Copenhagen, Øster Farimagsgade 2C, DK-1353 Copenhagen K, Denmark. 4. Queen Sirikit Botanic Garden, P. O. Box 7, Mae Rim, Chiang Mai 50180, Thailand. * Corresponding author. Tel.: +66 5446 6666 ext. 3254; E-mail: [email protected] (Manuscript received 15 January 2013; accepted 24 May 2013) ABSTRACT: Research on the pollination of Sirindhornia monophylla (Collett & Hemsl.) H. A. Pedersen & Suksathan was carried out in W Thailand, 2010‒2012. The orchid is a nectariferous, non-autogamous and self-compatible terrestrial. During 120 man-hours of flower watching, three species of Ceratina were found to be the main pollinators, viz. C. (Ceratinidia) lieftincki van der Vecht, C. (C.) collusor Cockerell, C. (Pithitis) smaragdula (Fabricius), males and/or females. Braunsapis hewitti (Cameron) was a minor pollinator. Ceratina acquired pollinia on their forehead and in some cases they subsequently deposited massulae on the stigma of other S. monophylla flowers. Three further species, viz. Ceratina (Ceratinidia) accusator Cockerell, C. (C.) chiangmaiensis W., M. & L. and C. (C.) bryanti Cockerell, did not acquire pollinia; but in these cases all pollen in the visited flowers had already been removed by previous pollinators. Ceratina belongs to family Apidae, subfamily Xylocopinae, tribe Ceratinini, whereas Braunsapis belongs to tribe Allodapini. Fruit set was nearly 50%. This is the first detailed account on the pollination of a Sirindhornia species, a recently described genus with three species, all included in the Thai redlist. KEY WORDS: Apidae, Braunsapis, Ceratina, Orchidaceae pollination, Sirindhornia, Xylocopinae. INTRODUCTION knowledge of the pollination biology of individual orchid species is widely acknowledged as being highly The genus Sirindhornia H. A. Pedersen & important for their long-term conservation (Roberts, Suksathan, named after H.R.H. Princess Maha Chakri 2003; Pemberton, 2010). In this paper, we contribute to Sirindhorn of Thailand, was described in 2003; it fill the information gap for S. monophylla. belongs to subfamily Orchidoideae, tribe Orchideae, Sirindhornia monophylla (Fig. 1) is fully subtribe Orchidinae and accommodates three terrestrial self-compatible, but non-autogamous, as demonstrated species that occur in open limestone habitats at experimentally by Srimuang et al. (2010a). 800–2200 m altitude (Pedersen et al., 2003). Consequently, it depends on pollinators for fruit Sirindhornia mirabilis H. A. Pedersen & Suksathan and production in its natural habitat. With its zygomorphic, S. pulchella H. A. Pedersen & Indham. are narrow more or less horizontal, mainly white to purple flowers endemics from northern Thailand, whereas S. that exude nectar hidden in a spur and offer an enlarged monophylla (Collett & Hemsl.) H. A. Pedersen & lip as a landing platform (provided with tufts of Suksathan is more widespread; its only population in coloured papillae that serve as nectar guides), the Thailand is sympatric with S. mirabilis. All three species fits the bee pollination syndrome of van der Pijl species are included in the National Thai redlist and Dodson (1966). In the study covered by this paper, (Santisuk et al., 2006) – S. monophylla being classified we attempted: (1) to identify its legitimate pollinators, as "rare" (R), the other two species as "endangered" (2) to reveal the pollination mechanism and (3) to (EN). Srimuang et al. (2010a, 2010b) provided observe and describe the behaviour of pollinators in comprehensive information on aspects of demography, relation to S. monophylla. This is the full paper recruitment, breeding system, flowering phenology, underlying an oral presentation given by K.S. at The 8th male and female reproductive success and patterns of International Symposium on Diversity and fruit set in all three species. In contrast, very little and Conservation of Asian Orchids, held in Shenzhen, fragmentary information on their pollination biology China in 2012 (abstract: Srimuang et al., 2013). has been published up to now (Srimuang et al., 2010a; Watthana et al., 2013). This is a serious gap, since MATERIALS AND METHODS 163 Taiwania Vol. 58, No. 3 Fig 1. Morphology of Sirindhornia monophylla. A: Habit. B: Floral morphology (anther largely hidden by the petals). Abbreviations: bu, bursicle; ds, dorsal sepal; en, entrance of spur; li, lip; ls, lateral sepal; pe, petals; sp, spur; st, stigma. Photos by K. Srimuang. Functional morphology of the flower Flowering phenology The inflorescence (Fig. 1A) measures 5–14 cm in The flowering season lasts from mid-May to early length on a peduncle of 7–26 cm, and bears 11–68 July, with a peak from the end of May until mid-June. individual flowers (improved data from previous The longevity of individual flowers is approximately 3 findings; Srimuang et al., 2010a). The flower (Fig. 1B) weeks (but if pollinated, the flower withers in 3 days). is 0.8–1.2 cm in diameter, white to pale rose with Flowering starts from the bottom of the inflorescence numerous tufts of purple papillae on the lip. In the and progresses to the top. resupinate flower with incurved sepals and petals, the lip (offering a landing platform) measures 3.4–6.8 × Study site and methods 4.1–8.4 mm. It is more or less 3-lobed in its distal part The study was carried out at Umphang Wildlife and provided with a basal, nectariferous spur that is Sanctuary, Tak Province, W Thailand. The habitat was nearly cylindrical, somewhat downcurved, 4.5–7.7 mm craggy limestone mountains approximately 800–1,000 long and 0.8–1.8 mm in diameter at the entrance. m a.s.l. The plants grew in grassy patches on slopes Glucose content of the nectar is approximately 5–10 covered by open forest with Strobilanthes spp. mg/ml. The straight to slightly recurved column is (Acanthaceae); Onosma burmanicum Collett and 1.5–2.8 mm long and provided with a subterminal, Hemsley (Boraginaceae); Leptodermis crassifolia erect, 2-loculate anther and a concave stigma on its Collett & Hemsl. (Rubiaceae); Quercus helferiana A. lower front. The rostellum is porrect and then strongly DC. (Fagaceae) and Buxus sp. (Buxaceae) as dominant recurved (in a knee-like bend) to form a narrow fold species. Population density of flowering plants of between the anther locules; the knee-like bend forms a Sirindhornia monophylla per area under observation single 2-loculate bursicle that is narrowly hinged at its (mostly 2 by 3 meters) was 3–5. A total of c. 20 lower margin. The pollinarium consists of two separate flowering individuals were kept under observation for hemipollinaria, each composed of a basitonous, clavate pollinator visits. pollinium and a minute viscidium, the latter being Pollination behaviour was recorded by field notes, completely hidden in the bursicle. Each pollinium is photographs and videos (by K.S.). When observing the composed of a long, sterile caudicle at base and a fertile orchids from some distance (3–5 m) in order to reduce distal part where the pollen grains are assembled in possible human impact (body odours, visual numerous, loosely attached massulae. distraction)on insect visitors, binoculars or monoculars 164 September, 2013 Srimuang et al.: Natural pollination of Sirindhornia monophylla were used. Observations were made from 27 May to 1 Observations on pollinators June 2010 (54 h, one person), 30 May to 2 June 2011 The main pollinators of S. monophylla were found (24 h, one person) and 31 May to 2 June 2012 (42 h, to be small carpenter bees, subfamily Xylocopinae, tribe two persons). The observation time was from 8:30 AM Ceratinini, viz. Ceratina (Ceratinidia) lieftincki van der until 5:00 PM, with a total of 120 man-hours watching Vecht, C. (C.) collusor Cockerell and C. (Pithitis) time. smaragdula (Fabricius) (Table 1, Fig. 2). Braunsapis It soon became clear that the main pollinators were hewitti (Cameron), an exponent of the tribe Allodapini, small carpenter bees (Ceratina spp.), cf. the Results was a minor pollinator. However, three further species, section below. Generally, only those Ceratina bees that viz. Ceratina (C.) accusator Cockerell, C. (C.) settled on S. monophylla flowers were collected; chiangmaiensis W., M. & L. and C. (C.) bryanti collecting all Ceratina that approached the flowers Cockerell, almost certainly are also legitimate would have reduced the chance of pollination. This, pollinators. They failed to acquire pollinia when visiting however, prevented exact identification of Ceratina the flowers, but in these cases all pollen in the visited which did not settle on the flowers and, hence, the flowers had already been removed by previous frequency of the various species in the habitat. Insects pollinators. were collected by net or a plastic box held over the Insect activity was mainly from 10:00 AM until flower/inflorescence, and subsequently euthanized by 4:00 PM. Pollinators tended to circle around the ethyl acetate. In S. monophylla successful removal and inflorescence or approached it in a zig-zag manner deposition of pollinia by the pollinator depend on its before flying straight to, and landing on, a lip (Fig. 2A), appropriate head width – if too small the head will not possibly visually attracted to the numerous tufts of touch the anther, if too large it cannot enter the flower purple papillae functioning as nectar guides. Generally, to contact the anther. Head width in set specimens was they crawled around, up and down, the flower. They measured by micrometer under a stereo microscope. then often flew off, but about one in ten entered the For the assessment of fruit set, four plots of 15–100 central interior part of the flower (i.e.