Journal of Threatened Taxa | www.threatenedtaxa.org | 26 March 2019 | 11(5): 13625–13628

Pollinators of Sikkim Mandarin Orange Citrus reticulata (Sapindales: Rutaceae)

Urbashi Pradhan ¹ & M. Soubadra Devy ²

^1,2 Ashoka Trust for Research in Ecology and the Environment (ATREE), Royal Enclave, Srirampura, Jakkur, Bengaluru, Karnataka 560064, India.

¹ Manipal Academy of Higher Education,Tiger Circle Road, Madhav Nagar, Manipal, Karnataka 576104, India

¹ urbashipradhan@gmail.com (corresponding author), ² soubadra@atree.org

Sikkim Mandarin Orange (Citrus reticulata Blanco, 1837) is a member of the Rutaceae family and a commercially desirable variety of the mandarin group native to Sikkim.  The Sikkim Mandarin Orange (SMO) growing area lies at an altitudinal range of 700–1,500 m and it is an annual flowering plant. Mandarin orange is dependent on bees for its pollination and pollinators help in higher yield and increased fruit set (ICIMOD 2003). Irrespective of large cardamom yield decline due to pollinator deficiency in Sikkim (Sinu & Shivanna 2007), till date there exists no systematic study on the range of pollinators for SMO.  This study aims to bridge this gap especially when a large proportion of farmers are dependent on the SMO for cash income.

Our study area spanned the East, West and South districts of Sikkim.  The southern part of the state, which lies in the altitude range of 600–1500 m provides an ideal climate for SMO cultivation (DHCCD 2015).  Data was collected across 72 SMO orchards from 2011 to 2013.  These orange orchards were selected within an altitudinal gradient of 700–1,452 m and were spread across 316km² (Fig. 1).

Pollinator visitation: At each site, 150 flowers were tagged and observed from 08.00–17.00 h to record insect species that visit them.  Intra-floral foraging behavior of each insect species was carefully observed to note whether it is a pollinator or a forager.  SMO bear self-fertile, bisexual flowers and pollen movement is facilitated by pollinators.  Transparent plastic bags were used to trap insects visiting the flowers to avoid any fruit loss during their collection.  Collected samples were preserved in 70% ethanol and subsequently identified in the laboratory.  Insects which were not seen touching the flower reproductive parts were not collected for identification.

We recorded 24 species of insects during the study period (2011–2013).  Common Honey Bee Apis cerana was the most dominant pollinator followed by hoverflies belonging to eight genera, namely, Episyrphus sp., Melanostoma sp., Ischiodon sp., Eristalis sp., Eristalinus sp., Scaeva sp., Episyrphus sp.,and Eupeodes sp. (Image 1,2) .  This was followed by stingless bees (Hymenoptera), seed bug (Hemiptera), and beetles (Coleoptera) that were sparse visitors.  Recorded insects were both pollen and nectar feeders.  Bees (Hymenoptera) and hoverflies (Diptera) visited flowers in groups while most of the beetles and seed bugs visited individually.  All the insects landed on the petal and foraged for pollen placed on top of the flower and nectar at the flower base.  In this process all the insects invariably touch both anther and stigma of SMO flower.  An insect visitor was called a pollinator when the ventral side of insect’s body containing pollen load touched the reproductive part of flowers.

SMO is an evergreen plant showing flowering response to early monsoon shower starting in the mid of February.  Flowering period lasts for a month, from late February to early April.  Orchards in the lower altitude starts flowering earlier followed by orchards in the higher altitudes.  Flowers are white in colour with strong scent attracting a range of insects for pollination.  Highlighting the importance of pollinators of the mandarin orange, in a study conducted by the International Center for Integrated Mountain Development (2003), pollination was seen to increase the yield of mandarin orange  by  four times compared to pollinator excluded flowers.  Honey bee (Apis sp.) has been reported as a major pollinator of different varieties of Citrus sp. from across the world, for example, Mandarin orange Citrus reticulata in Nepal is pollinated by A. cerana, A. dorsata, A. florea, and A. mellifera (International Center for Integrated Mountain Development 2003).  Kinnow Citrus reticulata, a hybrid between mandarin orange and sweet lime, was reported to be pollinated by A. dorsata and A. florea in Pakistan (Manzoorul-Haq et al. 1978).  Results of our study show only A. cerana visited mandarin orange flowers, while A. dorsata or A. florea, which were recorded in other studies, were not observed even outside our experiment sites during the study period.  Hoverflies, although not reported as pollinators of mandarin oranges earlier, are known to pollinate rapeseed oil (Jauker & Wolters 2008), apple (Solomon & Kendall 1970), and strawberries (Kendall et al. 1971). Both bees and flies visited flowers in groups and visited more than one flower at a time, possibly aiding in cross/sexual pollination (Raju et al. 2012).  Visits by other taxa such as butterflies, stingless bees, and beetles to orange flowers were less in comparison to bees and flies.  However, the importance of these wild pollinators in sustaining pollination of SMO needs further exploration.

Table 1. Pollinators of Sikkim Mandarin Orange.

For figure/image  -- click here

References

DHCCD (2015). AgriSkm. Available from: http://sikkimagri.gov.in/General/Eng/CropsDetails.aspx?ID=23. Accessed on 22 September 2015.

ICIMOD (2003). A report:  Cash Crop Farming in Nepal: The importance of pollinator diversity and managed pollination in Citrus.    International Center for Integrated Mountain Development  Jawalakhel, Kathmandu, Nepal, 49pp

Jauker, F. & V. Wolters (2008). Hover flies are efficient pollinators of oilseed rape. Oecologia 156: 819–823. https://doi.org/10.1007/s00442-008-1034-x

Kendall, D.A., D. Wilson, C.G. Guttridge & H.M. Anderson (1971). Testing Eristalis as a pollinator of covered crops. Long Ashton Res Stn Rep 1971: 120–121.

Manzoorul-Haq, M. Rafie-ul-Din & A. Ghaffar (1978). Effect of insect pollination on fruit bearing in Kinnow mandarin (Citrus reticulata), and physical and chemical properties of the fruit. Journal of Apicultural Research 17: 47–49.

Raju, A.J.S., P.V.S. Rao, R. Kumar & S.R. Mohan (2012). Pollination biology of the crypto-viviparous Avicennia species (Avicenniaceae). Journal of Threatened Taxa 4: 3377–3389. https://doi.org/10.11609/JoTT.o2919.3377-89

Sinu, P.A. & K.R. Shivanna (2007). Pollination biology of large cardamom (Amomum subulatum). Current Science 93: 548–552.

Solomon, M.E. & D.A. Kendall (1970). Pollination by the syrphid fly, Eristalis tenax. Available online at http://agris.fao.org/agris-search/search.do?recordID=XE20122001901. Accessed on 17 September 2015.