There are 265 species of Bumblebees (Hymenoptera: Apidae) reported worldwide, (
Williams et al., 1998; updated online at
http://www.nhm.ac.uk/research curation/research/projects/bombus/index.html). They are very important and efficient pollinators capable of foraging outside even in harsh and unfavorable conditions as compared to other types of bees
(Abak et al., 2000; Semida and Elbanna, 2006). Kearns and Thomson, 2001 studied that the bumblebees occurring at different altitudinal level starting from 1000 m and up to 5500 m ASL. These bees build their nests either in uninhabited rodent burrows or in the ground or in tall grasses.
O’ Toole, 1994 showed that the bumblebees are significant component of an agro-ecosystem and are completely depend on nectar and pollen resources. Hence, bumblebees are considered as important group to study the link between pollinator and floral diversity and playing an essential role in conserving the high altitude vivid vegetation.
Goulson et al., 2008a made a detailed study and reported that these insects inhabit distinct ecological habitat with their flower-patterned foraging activity. In addition
Williams and Osborne, 2009 confirmed that at last a few important species of bumblebees are required to preserve the natural flora and fauna.
Bumblebees are also considered as keystone species in most terrestrial ecosystems because the nests of bumble bees support a wide range of commensal and parasitic animals
(Goulson et al., 2008b). These insects are able to pollinate by producing vibration with their flight muscles rapidly and thus dislodge pollen from anthers
(Wahengbam et al., 2019). Unlike bumblebees, Honeybees vibrate their flight muscles slowly, therefore, they are considered to be incompetent pollinators for plants which need buzz pollination
(Averill et al., 2018). In 1998
Goulson et al., found that these bees left fragrance after visiting flowers and prevents other insects from visiting that flower again until the fragrance diminishes. These insects use signals for rewarding different types of flowers they visit or identify the visit performed by other insect pollinators (
Saleh and Chitttka, 2006;
Saleh et al., 2007 and
Pearce et al., 2017). The foraging activity of bumblebees is usually from 9:00 to 11:00 am as reported by
Abak et al., 2000 and
Chauhan 2011. However, they extend their foraging activity with reduced vigour from 13:00 to 14:00 pm.
The bumblebee pollinators favour brightness and dry climate as compared to rainy, cloudy and moist weather conditions and choose those flowers, which develop on the unlocked slopes of hill
(Raina et al., 2019). Heinrich, 1979a reported that bumblebees are able to forage at moderate temperature and light intensity in various agricultural crops.
Dramstad, 1996 and
Osborne et al., 1999 studied that the bumblebees frequently forage from their nests at a very significant distance.
Westrich, 1996 studied that the minimum requirements for the survival of bees including nest sites and other nest building materials and availability of floral resources like nectar and pollen.
Most of the wild plants are mainly pollinated by different species of bumblebees (
Goulson, 2003a).
Waser et al., 1996 stated that the major insect-pollinated plants use different groups of pollinators and most species of bumblebees are generalist pollinators. The consequences of elimination of extremely linked individual pollinators such as bumblebees from pollination networks created the maximum decline with respect to plant diversity
(Memmott et al., 2004). Bumblebees have always been a matter of fascination for humankind because of their attractive colours and potential to carry out indispensable pollination services in several agricultural crops among the insect pollinators (
Free and Butler, 1959;
Plowright, 1996;
Michener 2000;
Abrol and Shankar, 2013). Bumblebees are widely studied insect groups among other bees (Hymenoptera: Apoidea) and have been evaluated worldwide for its status as a threatened species (
Winfree, 2010).
Westrich, 1996 reported that the species of bumblebees are polylectic, which means they can forage on a number of floral species and well-tailored to live in human conquered scenery as compared to other olgolectic or oligoleges bee pollinators. In addition to this, bumblebees are found to forage in different mountain regions and are directly associated with different varieties of wild and cultivated flowers. They are capable of recognizing the flowers through floral temperature
(Harrap et al., 2017) and detection of electric field
(Clarke et al., 2013). They have also been noticed that these insects relatively favour symmetrical flowers than asymmetrical ones (
Moler, 1995;
Moller and Sorci, 1998). And from the symmetry the bilateral symmetry is chosen over radial symmetry (
West and Laverty, 1998).
Raina et al., 2019 observed that in the upper Indian Himalayas predominantly the trees of less alpine meadows between 3500 m to 5400 m asl and the vegetation that is conserved predominantly by the species of bumblebees include wide range of herbs, shrubs, grasses and medicinal plants having small flowers. The hostile and extremely severe environment of these snow clad mountains, predominantly the Apharwat range, Leh-Ladakh of Jammu and Kashmir and Lahaul-spiti regions of Himachal Pradesh where only some preferred species of medicinal plants are maintaining their existence, therefore bumblebees play incredibly a positive and decisive role in developing and conserving them. The common vegetation existing at these ranges and mostly pollinated by these bees include
Anaphalis busua DC,
Circbita cineria Linn.,
Senecio chrysanthemoides DC,
Taraxacum officinale,
Saussurea jacea (Klotz) Cl.,
S. albescens,
S. auriculata, S. lappa,
S. costus, S. fastuosa,
Scorzonera virgata, Senecio chrysanthemoides, Lactuca orientalis, Rudbeckia laciniata, Leontopodium alpinum, Tanacetum dolicophyllum (
Asteraceae)
, Potentilla atrosanguinea Lodd. (
Rosaceae)
, Thymus serpyllum Linn.,
Mentha longifolia Linn.,
Phlomis bracteosa Royle, Stachys serecia Wall. Ex Benth.,
Nepeta discolor Linn.,
Hyssopus officinalis Linn.,
Dracocephalum heterophyllum Benth.,
Nepeta laevigata (D. Don) Hand-Mazz. (
Lamiaceae)
, Polygonum amplexicaule D. Don. (
Polygonaceae)
, Pedicularis pectinata Wall.,
Euphrasia officinalis (
Scrophulariaceae)
, Gypsophil cerastioides D.Don (
Caryophyllaceae)
, Melilotus officinalis (L.)
Pall (
Leguminosae), Myosotis sylvatica Ehrh. Et Hoffm. (
Boraginaceae)
, Cyanthus lobatus Wall. (
Campanulaceae)
, Gypsophila cerastioides (
Caryophyyaceae)
, Rhodiola crenulata Linn.,
Sedum ewersii Ladeh (
Crassulaceae) and
Hyoscyamus niger Linn. (
Solanaceae)
. Hence, this long list of plants above clearly shows that the most of the high-altitude vegetation is mostly conserved by the bumblebees.
Abak et al., (1997); Kwon and Saeed, (2003) and
Velthius and Van Doorn, (2006) studied that in worldwide some important bumblebee species
viz.,
B. impatiens, B. occidentalis and
B. terrestris were employed for the commercial pollination of major agricultural cropping system. They have made a detailed study that the systematic hydroponics and polytunnel farming require such pollinators for crops like tomato, cucumber, pepper, strawberries
etc. The pollination performed by different species of bumble bees helps in the fruit quality with respect to weight, size, color and improved fruit set, to get cost effectual seed production
(Klein et al., 2007 and
Aizen et al., 2008). It has been established that bumblebees are vital and effective insect pollinators than honey bees for cucumber, watermelon and Apples
(Stanghellini et al., 1997; 1998 and
Thomson and Goodell, 2001).
Bumblebees have fewer tendencies to swarm as compared to honey bees and visit extra numbers of flowers per minute with a fly speed of 64 km/h, hence it is more suggested for pollination in green house cultivation
(Wahengbam et al., 2019). The body of bumblebees is furry than honey bees, therefore, it makes them relatively more perfect for collecting and transferring the pollen,
i.e., while bumblebees are foraging on flowers of raspberry plants and considerably deposited extra pollen on the stigma than honeybees
(Willmer et al., 1994). Klein et al., (2007) revealed that globally honeybees are significantly important for crop pollination as it is supposed to contribute 80% of insect pollination
(Robinson et al., 1989). Pollination is very important for the conservation of natural ecosystem and for the production of wide range of horticultural and agricultural crops (De
Groot et al., 2002; Hein et al., 2006 and
Eardley et al., 2006). The agricultural crops such as tomatoes, vegetables, peppers, cucumbers, seed crops, blueberries, cane berries, strawberries, squash and melons are more convenient with bumble bee pollination (
Anonymous, 2019).
Henrich, 1979b demonstrated that the bumblebees are economically important insect pollinators and play an important role as pollinators of wild flowers and some important agricultural crops. In North America it is estimated that 30% of the food for human being originate from plants pollinated by bees. Honey bees are generally considered as most frequent pollinators and have been studied extensively worldwide although bumblebees are the main pollinators of alfa alfa, clover, (
Trifolium spp.), plum and raspberries blossoms. While honey bee pollination in Norwegian orchards is mainly restricted due to low temperature, therefore pollination is mainly caused by bumblebees (
Faegri and Vanderpijl, 1979). Some species of bumblebees are being reared on commercial scale and put up for sale to farmers in various parts of the globe for the pollination of major cropping systems (
Pratap and Pratap, 1997,
2000).
Raina et al., (2019) extensively studied and confirmed that some species of bumble bees feed overwhelmingly on some plants such as
Cirsium falconeri,
Cirsium arvensis,
Nepeta spp.
, Carduus spp.,
Saussurea spp.,
Impatiens balsamina,
Prunella vulgaris, Trifolium pratense and
Trifolium repens. On the other hand, there are several other plants like,
Swertia spp.,
Artemisia spp.,
Indigofera spp. and
Pedicularis pectinata, which inspite of that occur in close vicinity to the above mentioned plants, they are occasionally visited by bumble bees.
Osborne et al., (1999); Walther and Frankl, (2000) and
Dramstad et al., (2003) studied that bumble bees with a ground speed of 54 km/h are able to forage up to 1-2 km from their colony and have been known for their flower constancy. The flowers identified by long-tongued bumble bees inserted lapping tongue for collection of nectar, while short-tongued bumble bees does not help in pollination as they rob nectar from flowers with a long corolla tube by biting at the base of the corolla (
Maloof, 2001). In Colorado, a sharp decline in the population of honey bees had apparently led to the short tongued bumblebee’s population (
Plowright and Laverty, 1984).
Leach and Drummond, 2018 made a detailed study that the opus of pollen and nectar plays an indispensable role for the nutrition and foraging behavior of bees.
Corbert et al., (1993) studied that bumblebees are very competent pollinators to work at very low temperature due to their thermoregulatory abilities and are found to be sufficient throughout the season. Therefore, they act as significant pollinators, particularly in the early blossoming period as well as in high land ecosystem (
Kevan and Baker, 1993;
Yu et al., 2012). Velthius and Van Doorn, 2006 projected that bumblebee colonies at large scale level are being commercially exploited and are large number of colonies are being marketed per year in the developed countries of the world for pollination purposes. Hence, bumble bees become ecologically and economically valuable insect pollinators.
Dias et al., (1999); Winter et al., (2006) and
Goulson, (2010) estimated that many species of bumblebees are commercially utilized for the glass house cultivation throughout the world and that has resulted to provide billions of dollars annually.
Bombus terrestris one of the major pollinator among bumblebees having highest pollination potential has been introduced in many countries
viz., Japan, Argentina, New Zealand and Chile for green house pollination (
Goulson, 2003b;
Winter et al., 2006).
Velthius and van Doorn, (2006) reported that the hothouse tomatoes mainly pollinated by bumblebees in the mid-1980s were found to be extremely productive, economical and put back effort demanding perfunctory process of pollination. Furthermore, they also reported that in 2004, pollination by bumblebees has yielded ca 99,000 acres of tomato production under the green house farming with an estimated cost of $ 15 billion worldwide. Bumblebees more adequately perform vibration to shed pollens from anther to stigma in tomato pollination as compared to honey bee (
Van Heemert et al., 1990).
Free and Butler, (1959) stated that bumblebees are more frequently used in glass house farming,
e.g. Kiwi fruits, tomatoes and cabbage pollination in Holland. The authors also studied that due to the wide spread of
Varroa jacobsoni and augmentation of poly house farming, resulted in a sharp decline in honey bee population and consequently the economic importance of bumblebees will possibly enhance. Griffiths and Robberts, 1996 noticed that the increased human population worldwide emphasizes the utilization of bumblebees to pollinate agricultural crops grown under intensive cultivation.
Macfarlane et al., (1985) made a detailed study on bumble bees and honeybees as pollinators of
Trifolium pratense in New Zealand. They observed that long-tongued bumblebees and pollen collecting honeybees act as main pollinators of red
Trifolium pratense. It was also observed by them that a single species of bumblebee could pollinate enough flowers to produce 0.3-0.6 kg crop seed in reasonable growing conditions.
Abrol, 1991 made a comprehensive studies on bumblebees in association with pollination of brinjal flowers in J and K. He recorded 7 species of bees distributed over 4 families, attracting the brinjal flower. Of these, bumblebees,
viz. Bombs asiaticus,
B.
albopleuralis and
B.
simillimus, were not only predominant visitors, but also efficient pollinators, whereas honeybees (
Apis cerana, A. mellifera), the carpenter bee (
Xylocopa valga) and the halictine bee (
Lassioglossum sp.), visited less frequently and in few numbers. In European Countries crops such as red clover, oilseed, alfalfa, field beans and other squashy and hard fruits are mainly pollinated by different species of bumblebees
(Corbet et al., 1991).
Arbetman et al., (2013) confirmed that bumblebees were exploited commercially beyond their inhabitant range, ensuing the increase of diseases to indigenous bumblebee populations and augmentation of exotic bumblebees
(Morales et al., 2013). Padilla et al., (2017) deliberated that in many countries, proper methodology is being developed for the commercial exploitation of the indigenous bumblebees of the respective region. Two species of bumblebees
viz.,
Bombus breviceps and
Bombus haemorrhoidalis in Vietnam and India are being reared
(Chauhan et al., 2014 and
Thai and Van Toan, 2018) and is first step to produce native species of bumblebee population for commercial pollination.
Deka et al., (2011) studied that both species of bumble bees are common in the north-eastern states and will prove very remarkable pollinators for several crops.
Gallai et al., (2009) estimated that the pollination service extended by insect pollinators and mostly by bees to agriculture worldwide has economic value of nearly USD 193 billion. In Ontario’s economy, commercially reared bumble bees are the principal pollinators in glasshouses and the crops they aid to pollinate contribute roughly USD 502 million each year
(Pindar et al., 2017). The pollination of crops through bumblebees was found to be cheaper as compared with perfunctory pollination in Belgium and Netherland (
Roulston and Julier, 2009).
Goulson, (2003b) studied that bumblebees are responsible for maintaining the seed production of majority of the crops and fruit trees. In Europe crops like beans are mostly pollinated by long tongued bumblebees resulting in good yields (
Free and Williams, 1976). The most important factors responsible for population decline of bumblebees in different regions of Asia, Europe and North America are manipulation of agricultural practices, pesticide poisoning and loss of habitat (
Free and Williams, 1973;
Rasmont, 1988).
