MSc

The present investigation entitled “Pollination efficiency of stingless bee, Tetragonula iridipennis (Smith) in cucumber (Cucumis sativus L.) under protected cultivation” was conducted in the polyhouse at College of Agriculture, Vellayani from November 2019 to February 2020. The objective was to evaluate the effect of pollination by stingless bee (T. iridipennis) on fruit set, yield and quality of salad cucumber under protected cultivation.
The foraging behaviour of T. iridipennis inside the protected environment was observed to evaluate their diurnal variations in resource collection and pollination ability in cucumber flowers. Observations on mode of alighting of bees, foraging behaviour of stingless bees, floral biology of C. sativus and pollination efficiency of stingless bees in terms of the quantitative and qualitative parameters were recorded.
Most of the observed bees were side workers (78 %), which landed on the petals and proceeded towards the reproductive part (stamen or stigma) while the rest of the foragers (22 %) were top workers, which landed directly on the top of stamen or stigma. Foraging rate was the highest (6.80 male flowers 5 min-1) during the time of initiation of foraging (0800 – 0900 h), while maximum foraging intensity was recorded as 4.40 bees male flower-1 10 min-1 during 1000 – 1100 h. Maximum time spent by pollen collectors per male flower was recorded as 44.20 sec. during 1200 - 1300 h of the day during which maximum pollen grains were observed from the body of the bees.
Irrespective of the time period, stingless bee spent significantly more time on female flowers compared to that of male flowers in respective time intervals.
The diurnal activity of a colony assessed in terms of the total number of incoming and outgoing foragers at the hive entrance revealed that their number increased with the ascent of the day, reached a maximum during 1300-1400 h (67.00 and 58.00 number of incoming and outgoing foragers respectively) and then decreased thereafter. Weekly
observations showed that the pollen and nectar foraging activity of stingless bees varies in a day with the peak period during 1200-1400 h.
A significant positive correlation was recorded between temperature and number of incoming foragers (r = 0.78) while a significant negative correlation was observed between relative humidity and number of incoming foragers (r = -0.68).
Studies on the floral biology as well as the morphology of bees has revealed that the individual nectar foraging bee insert its head into the corolla tube of both male and female flowers to reach the nectaries.
Significant increase in per cent fruit set was observed in stingless bee pollinated crop (76%) compared to hand pollinated one (54%) whereas the qualitative yield parameters like per cent malformed fruit, length and diameter of fruit were statistically on par. With regard to the quantitative yield parameters significantly higher single fruit weight, number of seeds per fruit and germination per cent (2 DAS) (685.00 g, 344.10 seeds/ fruit and 90.60 %, respectively) was recorded from the stingless bee pollinated crop than that of the control crop (555.00 g, 210.90 seeds/ fruit and 63.00 %, respectively). Higher yield was observed in augmented pollination (5.09 kg m-2) compared to hand pollination (3.16 kg m-2). Apart from this, bee assisted pollination was economically feasible with better B:C ratio (1.23) than that of the hand pollinated one (0.67).
The foraging activity of bees varied in a day with the peak period during 1200-1400 h. Stingless bee pollination had a profound influence on the per cent fruit set as well as the quantitative parameters like fruit weight, germination percentage and number of seeds per fruit. Augmentative pollination with stingless bee under protected cultivation resulted in increased yield of 61 per cent in C. sativus.