Current Issue

Bangladesh is a deltaic country formed by the floodplains of the three foremost rivers: the Ganges, Brahmaputra, and Meghna. These rivers ditch into the Bay of Bengal, although only 7% of the catchment area lies within the country’s precincts. Across the river banks on the southern coastlines, and north of the basin, are sandbars, accumulations of coarse sands. The northwestern corner, at the confluence of the Teesta River and the Brahmaputra River, is especially exposed to flooding and erosion. After each rainy season consequently with flood, large sand islands appear in the main rivers of northwest Bangladesh. These innumerable vast sandbars emerge in the riverbeds during the dry season (November-April). Most of these sandbars remain unused and barren because of their unfertile sandy traits (Rahman and Reza, 2011). In spite of this intricacy, the sandbar inhabitants have been growing pumpkins with technological assistance from an NGO, Practical Action Bangladesh (PAB). As pumpkin (Cucurbita pepo L.) is a monoecious, obligate cross-pollinated crop, so, transfer of pollen to the pistil of the female flower is essential (Delaplane and Mayer, 2000). Any pollinating agent or hand pollination is crucial for those crops. Commonly, very few pollinating agents are found in the sandbar areas due to lack of flora and pumpkin growers are usually fertilize the female pumpkin flowers by hand pollination. But it is cumbersome, laborious, sensitive and could not achieve 100% pollination success. While the insects ,especially bees are important pollinating agent and can be efficiently fertilize the flowers of the sandbar cropping system as well produce honey which can alleviate the poverty of the sandbar inhabitants. The seed set of pumpkin also depends on insect pollination (Fuch and Muller, 2004; Nicodemo et al., 2009). Although squash bee and carpenter bees are known efficient pollinators of pumpkin, honey bee, Apis mellifera L., is also a particu-larly important ollinator, especially in sandbar areas where other bees are absent (Hurd, 1964). For commercial production of pumpkins, honey bees are the only effective pollinator that can provide in sufficient numbers for adequate pollination (Free, 1993). Walters and Taylor (2006) reported that addition of a honey bee hive to a field of pumpkin increased the quantity of set-fruit by 62% and total fruit weight by 100% under field conditions where sufficient natural pollinators freely visited pumpkin flowers. Consequently, honey bee colonies are rented in large numbers by pumpkin growers for the elevation of pumpkin pollination. Farmers routinely supplement pumpkin fields with honey bee hives (Free, 1993) which is assumed to increase the visitation frequency to pumpkin flowers, and increase fruit yield.

Honeybees need several nutrients, like carbohydrates, proteins, lipids, vitamins, and minerals for their growth and development. They take carbohydrates from nectar and proteins from pollen (Javaheri et al., 2000). The pumpkin flowers are rich of pollen content but the amount of nectar is not sufficient due to hot and dry conditions of sandbar for meet up the food requirement of honeybee as well as honey production. As sandbar area does not have diversified crops so there is no way to meet up the nectar requirement from any other resources to increase the honey production. Supplementary foods can be fed to honey bees to supply the nutritive requirements of colonies as well honey flow in sandbar areas and at times when natural food sources (pollen, nectar, or honey) are inadequate or not available. Feeding bees with pollen substitute and sugar syrup increase the number of bees and frames covered by bees, brood area and colony weight (Sahinler et al., 2003).

Bee pollen is the food of the young bee containing high protein contents (Ghosh and Jung, 2017). It is considered one of nature's most completely nourishing foods. It contains almost all the essential components of proteins, free amino acids, and vitamins, including B-complex and folic acid for the diet of human which acts to enhance high-density lipoproteins (HDL), reduce low-density lipoproteins (LDL), and standardize blood serum cholesterol and triglyceride levels (Mercola, 2016). Generally pumpkin flowers are large and contain enormous pollen and sufficient amount of nectar. But the nectar dried up quickly due to hot sandy soil of the cropping area. Sugar is the main commodity to feed honeybees when availability of natural nectar becomes scarce. During the pumpkin growing season in sandbar, other natural nectar sources are also scarce. Thus, supplementary feeding of honeybee may be necessitated for proper colony development and pollination. Supplementary foods could meet up the shortage of nectar and encourages the bees to increase the population and pollen collection. This paper reports the experiment done in pumpkin cultivation system while feeding supple-mentary foods to the bee colonies.

Generally, supplementary feeding is required when bees are moved into flowering orchards, deficient bloom or during cloudy or bad weather or during package bee installation on undrawn comb, to overwinter and to promote colony extension for future colony divisions (Herbert 1992).Supplement artificial diets can also be effective in stimulating honey bee colonies to rear brood (Mattila and Otis, 2006; Nabors, 2000 and Standifer et al., 1973). The present experiment conducted at sandbar which is very hot during the day and so that the nectar of the pumpkin flowers usually dries very fast. Hence, the extra feeding to the bees can be enhancing the bee’s activities. However, supplied all the tested diets to the bees in the sandbar pumpkin fields were effective in stimulating brood rearing or number of combs covered with bees. Bee colonies provided with syrup-1 induced the highest amount of worker brood cells followed by syrup-4 and syrup-2 in the months of February and March. As the sugar quality and content of syrup-1 are high, so, it performs well than control and even any other syrup. Bees fed with various sugars helped to survive better, produced the same amount of wax per bee, and capped more honeycomb cells (Barker and Lehner, 1978). Sugar syrup has long been recognized as having a stimulatory effect, such as an increase in bee population, pollen-collecting activities (Barker, 1971). Free and Spencer-Booth (1961) observed bees switching their foraging strategy after sugar feeding to support colony brood rearing. However, sugar syrup has become more widely used to feed bee colonies because of it lower expense and ease of handling.

After March the sandy soil of the riverside area turned into hot very fast and the total environment became harsh for the pumpkin plants and bees. At that time the number of pumpkin flowers and bee activities reduced gradually which affected the bee population. Comparatively cooler temperature of February was better for increase the bee population and bees can produce much honey and pollen. Tested diets were differed in their consumption by bees;syrup-1 was completely consumed in comparison with other diets. Even though same amount of sugar and water was mixed for syrup -1 and 4 but the brown sugar used in syrup -4 did not perform as white sugar. Degrandi-Hoffman et al. (2008) suggested that differences in the nutritional quality of the supplementary foods and perhaps the digestibility and accessibility of their nutrients to worker bees influence the amount of brood that can be reared even when consumption rates are similar.

Colonies receiving syrup-1 had maximal bee strength and produced more honey than the other colonies. Somerville (1999 and 2000) used the thick sugar syrup (2/1 sugar/water ratio) to produce enough honey for winter and thin syrup (1/1 sugar /water ratio) to stimulate the colony to expand the brood area. Abdellatif et al. (1971) have reported the increased honey production from colonies feeding pollen substitute during dearth period. Chhuneja et al. (1992) reported that higher consumption of pollen substitute diet resulted in higher production of brood and more populous colonies produced significantly more honey. It is contented that stronger colonies store more honey as compared to the weak colonies (Kumar et al., 1995).

The pollen collection varied after providing supplementary foods. The colonies supplied with syrup-2 yielded the highest amount of pollen (2.615g). Actually pollen is used for bee brood rearingand bees preferred to mixing syrup-2 with pollen for brood food.

Honey bees have high search ability for flower resources, foraging optimally in terms of energy and time efficiency (Seeley, 1995). As only pumpkin flowers are available in sandbar so honey bees actively visit one species of flower in a bout. Floral visitation rates are one of the good indicators of pollination effectiveness (Javoreketal, 2002). Honeybees are not shown to be as efficient in other tested diets as compare to syrup-3 in terms of pollination efficiency per visit by an individual. The syrup-3 is composed of one part of white sugar and one part of water and it was most inferior syrup among the supplied supplemented foods. Flower visitation rate of honey bee was high in the field treated with syrup-3. In the case probably bees meet up their extra nutritional requirements by collecting excess pollen and that’s why visit frequency was high. Actually the conditions of the pumpkin plants belong to syrup-3 treated colonies were not vigorous as compared to other fields and the quantity and quality of flowers were not satisfactory. This might also be reason to high visit frequency.

However, honeybees belongs to supplied colonies incorporated with the pumpkin cultivation system are the major flower visitors in the sandbar pumpkin fields. They provided the service of pollination for pumpkin which increased the fruit succession rate as well as pumpkin production. Walter and Taylor (2006) reported that even under field conditions with sufficient natural pollinators, the addition of honey bees increased the production of C. pepo. From this research, it was evident that the supplementary foods supplied to the bee colonies were effective for bee population and production of bee pollen, honey and, pumpkin in sandbar pumpkin cropping system.

Honeybees provided with supplementary feed produced high number of brood cells and increased the bee population resulting in better pollination.