Pollination biology of large cardamom (Amomum subulatum Roxb.) with special emphasis on honey bees (Apis spp.) and bumble bees (Bombus spp.) pollinators

Abstract

We studied pollination ecology of large cardamom (Amomum subulatum) in three altitudinal gradients (1100, 1500, 2000 m) in the Sikkim Himalaya, with the hypothesis that both honey bees (Apis spp.) and bumble bees (Bombus braviceps, B. haemorrhoidalis) contribute to pollination and enhance yield. We placed honey bees colonies in cardamom stands, studied pollination within 50 m radius, 250 m away from it; and under control nets restricting pollinators. Honey bees showed highest number of floral visits (19.24 ± 4.23 per 12 m2) within 50 m than bumble bees (13.87 ± 3.12 per 12 m2). In 250 m stand, bumble bees visits (20.57 ± 5.31 per 12 m2) were higher than honey bees (9.44 ± 2.54 per 12 m2). Pollen removal by honey bees and bumble bees was 30–40% and 50–70% of the total pollen, respectively. Time spent across sites and treatments by honey bees ranged higher (12.87–36.25 s flower−1), than bumble bees (4.60–27.80 s flower−1). Visitation of bees increased with increasing number of cardamom flowers and showed positive correlation (r2 = 0.46–0.55, P < 0.001). Number of capsules per spike, capsule/seed weight, and gross agronomic yield was highest within 50 m, lower in 250 m and lowest in control confirming that honey bees pollinated stand had higher yield. The study also confirmed that both honey bees and bumble bees were pollen collectors and pollination is by-product of their foraging activity on the flowers. This study suggests new insight on contribution of honey bees to large cardamom pollination and further research is needed for pollinators-large cardamom interaction.