Proc. Indian Acad. Sci. (Anim. Sci.), Vol. 93, No.4, June 1984, pp. 373-390. © Printed in India. Bee-flower interactions and pollination potential C SUBBA REDDI and EUB REDDI Department of Environmental Sciences, Andhra University, Waltair 530003, India Abstract. This article presents the recent trends in describing the bee-blossom relationships, in interpreting the beesforaging behaviour on the basis of optimal foraging theory and the nature of floral resource, the role of pollinator behaviour such as trap-lining, opportunism, territorial aggression, group foraging in determining the geneticmake-up of the bee pollinated plants, and considering the pollination from the ecosystem point ofview. The idea that honey bees and other social bees are adequate enough to pollinate the crops is considered as premature, and detailed studies to explore the pollination potential of wild bees together with their conservation and management are suggested. Keywords. Bee-blossom interaction; foraging behaviour, pollination potential. 1. Introduction A very wide spectrum of insects visit the flowers for nectar and/or pollen, and are of much value in effecting pollination. Bees are among such insects. The bees require large food supplies for their brood, even hundred times of their own requirement, and to secure this food they make repeated. visits to the flowers. Thirty thousand bee species are estimated to occur in the world (parker and Torchio 1980).The majority are solitary bees distributed mostly among the families Colletidae, Andrenidae, Halictidae, Megachilidae, Anthophoridae and Xylocopidae. The family Apidae comprises mostly the social bees ofthe genera Apis, Bombus,Trigona and Melipona. Only about 1%ofthe world bee species is reported from India (Kapil and Jain 1980). Bees have long been recognised as effective pollinators. In the first half of the 18th century, Dobbs specificallymentioned that the bees may serve to transfer pollen (Grant 1949). But the credit ofrecognising bees as pollinators goes to Koelreuter who through extensive observations demonstrated bee role in pollination in 1761 (Faegri and Pijl 1979). Later in 1930 Reinecke emphasised the importance of the honey bee as pollinating agent (Lotter 1960). It is estimated that bees alone can accomplish more than 80% of the pollination by insects (Vansell and Griggs 1952; McGregor 1980). In California, bees alone participate in the pollination of more than 95 %of the insect pollinated plants (Moldenke 1976). Becauseoftheir vital role in fruit and seed production, and in determining the community structure, a lot has been done from early times on bees, bee-foraging, bee-pollination, and bee-management.Theaccumulated knowledge appeared in such books as Lovell (1920); Frisch (1950, 1967); Jaeger (1961); Meeuse (1961); Percival (1965); Free (1970a); Kugler (1970); Proctor and Yeo (1972); Kozin (1976); McGregor (1976); Frankel and Galun (1977); Free and Williams (l~77); Richards (1978); Faegri and Pijl (1979) and the reviews such as Grant (1950); Bohart (1952, 1972);Vansell and Griggs (1952);Todd and McGregor (1952); Manning (1956); Linsley (1958); Lotter (1960); Deodikar (1961); Pijl (1961); Baker and Hurd (1968); Stebbins (1970); Macior (1971, 1973, 1974a); Heinrich and Raven (1972); Martin and McGregor (1973);Covich (1974); Heithaus (1974); Levin (1974, 1978, 1979);Heinrich 373 374 C Subba Reddi and E U B Reddi (1975a); Kevan (1975a); Frankie (1976); Schremmer (1976); Pyke et al (1977); Vogel (1978a); Eickwort and Ginsberg (1980). We attempt here to summarise the recent developments and some of the aspects not covered in earlier reviews.. 2. Means of attraction Pollen, nectar, oil, liquid perfume, nest building materials, sexual attraction, odour and visual features are responsible for establishing a blossom-visitor relationship. 2.1 Pollen Bees require large quantities ofpollen to meet the protein requirements oftheir brood. Naturally to attract them the flowers have toproduce good amount ofpollen. However, bees may reject certain types ofpollen e.g. Euphorbia heterophylla (Reddi 1981).There are indications ofbees inability to recognize the nutritive value ofthe pollen collected. They may collect materials ofno value like flour, fungal spores, flakes ofpaint and coal dust (Wahl 1966).Pollen presentation times vary from species to species and are species specific (Reddi 1981, 1982);the bees appear to have time sense and forage in synchrony with the pollen presentation times. 2.2 Nectar Bee flowers mostly have deep-seated protected nectar with greater amounts ofsucrose. Bee visits to flowers depend on nectar concentration rather than on quantity (Rymashevskii 1976); the concentrations. are typically more than 20% (Percival 1965; Baker 1975) and if they are below, the honey bees 'work at loss' (Free 1970a). 2.3 Oil Oil has been added as an attractant to the earlier lists (Vogel 1969).Substitution ofoils for flower nectar is a special feature of desert flowers in California (Moldenke 1976). Krameria possesses 'oil flowers' offering fatty acids to female Centris bees for brood­ rearing (Simpson et al 1977a). 2.4 Odour and perfumes Euglossine bees collect odoriferous substances (liquid terpenes) from orchids and from a few non-orchidaceous plant groups. Though the total impact ofthis has not yet been assessed, it might be that it helps increasing the longevity ofmales, attracting females and in getting self-satisfaction due to narcotic effect. Nectarless orchids are pollinated exclusively by Euglossine males. Here it is the strong odour that draws the bees. In fact the bees collect the aromatic oil secreted by the flowers. To quote Kullenberg (1973), male bumble bees are "living perfume brushes". 2.5 Nesting materials Besides pollen, nectar, nutritive oil, perfume, the flowers offer still other products such as wax (Porsch 1905),and resins (Kirchner 1925; Cammerloher 1931)which are used in nest building. Bee-flower interactions 375 2.6. Visual patterns and pigmentation Many flowers have nectar-markers invisible to the human eye, but which can be brought out employing uv photography (Eisner et al 1969). It is remarkable that the honey bees when crossing the boundary between the uv-retlecting and the uv­ absorbing inner part ofa petal, automatically extend their probosces, as if they know they are to the source of nectar. 2.7 Colour Bee vision has been described as 'trichromatic'. This means they possess three types of photoreceptors which give maximum sensitivity at 360,450 and 650 nm. These three spectral points are uv, blue and yellow respectively (Daumer 1956; Mazokhin­ Porshnyakov 1962,1969). As the colours that bees perceive are not similar to those of humans, these are named according to insects visual spectrum as uv 'insect-blue' blue 'insect-green', and yellow'insect-red' (Kevan 1978). The bees are more prevalent on blue or purple tlowers (insect-blue to insect-green). They are generally considered as red blind, but Leppik (1955) mentioned thatTrigona bees could be attracted to red. Further, Thorp et al (1975) have suggested that nectar itself may absorb, reflect, or fluoresce daylight and act as another visual attractant. Eisner et al (1973) have described the uv patterns ofbuds and blossoms. The buds ofJasminum primulinum and of H yperacium sp are uv absorbing and as the buds open. the newly exposed petal parts reflect uv radiation. 2.8 Sexual attraction Attracting the bees through exploiting their sexual 'passion' is a well-known phenomenon in orchids (Arditti 1979). The Ophrys species, have 'tapped' the pheromone system ofbees and wasps. Each species of Ophrys attract males ofa limited number of species eg.' Andrena, Anthophora, Colletes, Eucera, Tetralonia, Melecta. These males attempt copulation with the flowers and effect pollination (Arditti 1979; Eickwort and Ginsberg 1980). Rendezvous pollination has been well described by Barrows (19700) and, Eickwort and Ginsberg (1980). 3. Deception in bee-blossom relationships Bee-blossom relations are not always mutualistic but sometimes parasitic also because of the deceptive nature of either bee or blossom. 3.1 Deceit on the part ofbees Pollen and nectar stealing by bees without performing the reciprocal service of pollination is very common. Small nectar gathering bees in N emophila menziesii (Cruden 1972), the honey bees which visit for nectar at dusk to a bat pollinated blossom Maranthes polyandra (Lack 1978), and small halicted bees which collect nectar in Asclepias verticillata (Willson et a11979) are some of the examples. Some bee species (Bombus, Xylocopa, Apis, Megachile, Melipona, Euplusia and Trigona) are known to get (Animal Sci.)-8 376 C Subba Reddi and E U B Reddi at the nectar by perforating the corolla bases ofsome blossoms (Percival 1965; Macior 1966,1970,1971, 1974b, 1982; Proctor and Yeo 1972; Barrows 1976b; Faegri and Pijl 1979; Roubik 1979). Honey bees may opportunistically collect nectar through the perforations made by robbers like bumble bees (Hawkins 1961). Instances of pollen stealing include Perdita bees flying in the late afternoon in the flowers of Mentzelia (Michener 1979) and on Opuntia (Barrows et al 1976) and the small bees (Perdita, Ceratina; Evylaeus) from Cactus flowers (Grant and Grant 1979;Grant and Hurd 1979; Grant et al 1979). Some bee species like Dialictus in Ludwiqia peploides (Estes and Thorp 1974), Ceratina in Tribulus terrestris (Subba Reddi et a11981) fail to touch the stigmas because ofsmaller body size and intrafloral behaviour. Honey bees which pay visits for nectar/pollen