The Indigenous Honeybee, Apis cerana â€" A Pollen Robber or Pollinator of Large Cardamom?; ICIMOD Working Paper 2017/8

Large cardamom (Amomum subulatum Roxb.) is the main cash crop and an important livelihood option for farming communities in the eastern Himalayas â€" especially Sikkim, parts of West Bengal, eastern Nepal, and southern Bhutan. The crop is self-fertile but requires cross pollination for production of capsules. Scientific information on the eco-biology of large cardamom pollination is scarce, but studies have shown bumblebees to be the main pollinators. Previous studies have indicated contradictory results on the role of indigenous honeybees, particularly Apis cerana, in pollination of large cardamom. Some studies reported that Apis cerana was a ‘pollen robber' that collects all the pollen from a flower without actually pollinating it, resulting in severe crop decline. However, beekeeping is common in large cardamom farming areas of Sikkim and Nepal and the bee is a common visitor to the flowers. Farmers in these areas have never observed a decline in large cardamom yield due to the presence of Apis cerana. This publication describes the results of a detailed investigation into the role of Apis cerana in large cardamom pollination, designed to establish whether the bee is a pollinator or pollen robber and determine its impact on crop yield and quality. The research was conducted on farmers' fields located at different sites in Sikkim, India: Lingee Payong (1,100 masl) and Hee Martam (1,500 masl) in West Sikkim, and Jaubari (2,000 masl) in South Sikkim. The methodology consisted of on-farm experimental research and data collection through regular field observations, and a review of the literature on large cardamom pollination. Three experimental procedures were used at each site: (i) observations of the foraging behaviour of Apis cerana bees on cardamom flowers, and the impact of pollination by Apis cerana and other pollinators on capsule yield and quality (capsule weight and number of seeds per capsule), in a plot with a medium-sized healthy colony of Apis cerana placed at the centre; (ii) observations of the foraging behaviour of bumblebees and other pollinators, and of capsule yield and quality, in a plot about 250 m away from the plot containing the Apis cerana colony; and (iii) observations of capsule yield and quality in plants caged in a nylon net (3 x 3 x 3 m) to exclude all pollinators as a control. The results of the study showed that Apis cerana is an effective pollinator of large cardamom. Although the Apis cerana bees are relatively small, they landed on the anther-stigma column of the cardamom flowers multiple times from different directions while collecting pollen which ensured that they also touched the stigma and thus pollinated the flowers. Other favourable foraging attributes included foraging throughout the day, visiting all flowers on a panicle and then moving on to another, and multiple visits to flowers. The favourable attributes translated into a 45% increase in yield compared to natural pollination in fields with a supplementary Apis cerana colony. The fruit set, seed set, and fruit and seed weight (capsule quality) were all significantly higher in plots with an Apis cerana colony than in plots without a colony or with all pollinators excluded. The results suggest that especially in areas where bumblebee populations and other natural pollinators are scarce, Apis cerana can be used to pollinate large cardamom to ensure a reasonable harvest and better quality capsules.