Proc. Indian Acad. Sci. (Anim. Sci.), Vol. 93, No.4, June 1984, pp. 373-390. © Printed in India.

Bee- interactions and 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 -blossom relationships, in interpreting the beesforaging behaviour on the basis of optimal foraging theory and the nature of floral resource, the role of 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 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 visit the for and/or , 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, , Anthophoridae and Xylocopidae. The family 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 . 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 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 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 . 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

( 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 at dawn to a bat pollinated blossom (Baker et al 1971; Lack 1978), and the pollen gathering honey bees in cucurbits already pollinated by matinal bees (Linsley 1960),and Trigona collecting pollen deposited on petals and leaves after dislodgement by large bees (Roubik 1979) come under scavenger bees.

3.2 Deceit on the part ofblossoms In 1793 Sprengel introduced the 'deception hypothesis' but it was not supported by contemporary workers. But the recent observations support the Sprengel's 'deception hypothesis' (Pijl and Dodson 1966;Nilsson 1979, 1980, 1983;Dafni and Ivri 1979, 1981; Ardetti 1979; Ackerman 1981; Boyden 1982; Dafni 1983; Meeuse 1983). Shifts from rewards to deception including heteranthery, anther dummy were nicely dealt with by Vogel (1978b). This deception phenomenon reached its excellence in some orchids.

3.2a Visual deception Dafni and Ivri (1981) reported that Orchis israelitica () and Beileualiafiexuosa (Liliaceae) have similar appearance and share the pollinators, and they describe it as floral mimicry. In Ophrys apfera, the pouched labellum resembles a bumble bee in shapeand marksand is pollinated by pseudocopu­ lation by males. Orchis galilaea mimics the females ofcertain wild bees and attracts the males (Meeuse 1983).Onchidium planilabre flowers imitate a flying insect, and a Centris male patrolling his territory takes it for an intruder (Ardetti 1979). The non-dehiscing anthers in pistillate flowers ofCupania guatemalensis serve the purposeofattracting bee visitors (Bawa 1977). These blossoms with heteranthery and other pollen saving deception practices like anther dummy maintain visits by a modest but real harvest, but pollen flowers oforchids resort to total deception producing powder like hair tufts or empty granular pseudopollen.

3.2b Olfactory deception This is mostly met with orchids. Males of Halictus marginatus are only attracted towards Orchis qalilaea, although female bees also are present in the neighbourhood (Bino et aI1982). In addition, the temporary/exploratory drives of bees for food sources are exploited by means of superiority in floral display (Nilsson 1981, 1983). There are cases of nectarless species mimicing the rewarding species (Macior 1971; Heinrich 1975b; Boyden 1980; Bierzychudek 1981; Williamson 1982)or one another (Schemske 1981)achieving pollination through their contribution to the attractive appeal of the community. But Orchis caspia, also a nectarless plant, achieves pollination exploiting the poor discriminative power of the bees; and not through resorting to mimicry (Dafni 1983). Bee-flower interactions 377

4. Bees are not exempted from errors

Though bees arevery clever/intelligent to manipulateany specialized and difficult floral mechanism, sometimes they too make mistakes; as a result they are succumbed to troubles, sometimes leading to death. Due to lack of balance between odour, dimension, and stickiness, some flowers (mostly hybrids in nature) become veritable death-traps, killing the visiting bees (Dodson 1975).

4.1 Killer traps/death traps Certain species ofAsclepias (Percival 1965; Proctor and Yeo 1972; Willson et al 1979), Wrightia tinctoria (Subba Reddi et al1979), kill all but the strongest bees in their 'clip and slot' devices. Certain species ofOrchids (Coryanthes rodriguesii, Gongora maculata, Cypripedium calceolus) are known to trap the bees such as Euplusia, Euglossa and Andrena by intoxicating them.

4.2 Collection of poisonous forage Under acute shortage of food the bees are forced to collect poisonous forage too (Deodikar 1961). The presence ofalkaloids, saponins, glucosides, phenolic substances and essential oils is mostly responsible for poisoning the bees (Baker and Baker 1975; Pottev et al1976). Sugary honey dew secreted by some homopteran insects and infected . leaves of certain trees also cause bee paralysis and large scale deaths (Butler 1943). Recently Barker and Lehner (1976) reported the toxicity of galactose containing exudates from . It may be recalled that the pollen collecting bee is not sensitive to the nutrient value of its forage (Wahl 1966). Apparently, the only regulator is the phagostimulant content which evidently makes all pollen attractive to the bees. This explains why bees collect pollen which is toxic to them (Wahl and Ulm 1983).

5. Energy expenditure vs energy gain

In recent times, flower visits by bees, ofcourse by all , arebeing explained on the basis of'optimal foraging theory' (Schoener 1971; Cody 1974; Covich 1974; Oster and Heinrich 1976; Pyke 1978a,b; Pyke et al 1977; Schaffer and Schaffer 1979;Waddington and Holden 1979;Kamil and Sargent 1981; Stephens and Charnov 1982;Bertsch 1983) which may be defined as that which yields the greatest net energy and nutrient gain per unit foraging time (Levin 1978). In other words, the amount ofreward per flower must be sufficient to justify a visit; but not so excessive as to limit successive flower visits (Heinrich 1975a). In a study on the interaction ofhoney bees with the artificial flowers, the results obtained by Wells and Wells (1983) are contrary to the optimal diet theory and the .minimal uncertainty. Most work on foraging energetics was carried on Bombus because of their high energy requirements (Heinrich 1972, 1975a,c,d; 1976a,b). The studies of Heinrich (1976a, b), Schaal (1978), Pyke (1978a, b), Real (1981) and Waddington et al (1981) suggest that bumble bees do assess variations in reward and forage for nectar in an optimal manner. The energy budget ofpollinator differs from species to species, mostly governed by body weight, and temperatures (Parrish and Bazzaz 1979). The energy 378 C Subba Reddi and E U B Reddi relations are critically discussed by Heinrich and Raven (1972). The bees working under low temperature need to expend more energy and the full nectar loads at the beginning of anthesis compensate for the extra energy expense, but those flying during higher ambient temperatures incur low energy costs, and the benefits are also low. Though the optimal foraging theory is still considered valid, energy alone is not the appropriate measure of fitness (Eickwort and Ginsberg 1980). Nectar may be important as a source ofwater than ofsugar for certain periods (Watt et al 1974).The need to consider water budget in the foraging behaviour has been stressed by Bertsch (1983). He felt that in view of the close interdependence between flowers and pollinators, the functions ofthe flowers and their adaptationscan only be understood if the needs of the insect visitors i.e., their water and energy requirements are known.

6. Sternotribic and nototribic pollen deposition

Two categories ofpollen transference by bees were recognised depending on the way in which pollen is deposited on insect (Percival 1965; Proctor and Yeo 1972; Macior 1974a;Faegri and PijI1979). In sternotribic flowers (e.g. 'flag blossoms' ofthe type seen in Fabaceae) pollen is deposited on the ventral side ofthe bee. In nototribic flowers (e.g. 'gullet blossom' of.the type seen in Labiatae, Scrophulariaceae, Acanthaceae and Gesneriaceae and of the Orchids) deposition is on the dorsal side of the bee. In the ofany pollination mechanism the strategy should be to achieve precision and economy in pollen transfer. This is possible through nototriby because the residual pollen on the body positions is inaccessible for grooming, thus guaranteeingsuccessful and regular pollination. Whether pollen deposition is nototribic or sternotribic depends on the topography ofthe blossom and the body size ofthe vector concerned (Macior 1982;Reddi and Subba Reddi 1983~ Beeswhile foraging must come in contact with the essential organs for successful pollination: One glaring exception to this is Wrightia tinctoria where bees without touching the essential organs aid in pollination (Subba Reddi et al 1979).

7. Temporal patterns of bee foraging

Bees normally forage during daylight hours. However, Linsley and Cazier (1970) recognize five temporal categories depending on foraging timings: matinal bees (e.g. Melitoma grisellaon Ipomoea leptophylla, Onagrandrena sp. on Oenothera dentata; Peponapsis, Xenoglossa on Cucurbita perennis, Ptiloglossa arizonensis on Solanum flowers (Linsley 1960, 1962),crepuscular bees (eg. Apis mellifera; Bombus sonorus, on Agave schottii (Schaffer and Schaffer 1977, 1979), nocturnal bees (eg. Sphecodogastra texana (Kerfoot 1967a,b); Xylocopa (Burkill i909; Bhaskar and Gopinath 1975;Grant and Hurd 1979),diurnal bees (majority of the bees), late afternoon bees (eg. Perdita wootonae on Mentzelia decapetala flower (Michener 1979),Perdita taxana on Opuntia flowers (Barrows et al 1976). These categories are mostly regulated by environmental conditions. In the arctic summer, bees forage all night long (Andrewes 1969). Sometimes when conditions (environmental and resource) permit, the diurnal visitors may start foraging early in the morning and compete with the matinal bees (Linsley Bee-flower interactions 379

1960); when resources are poor, foraging may be carried on further for an hour after sunset (Andrewes 1969). Large-bodied species tend to forage primarily in the relatively cool early hours when pollen and nectar are normally more abundant, while the smallest species scavenge for pollen from virtually bare anthers during the midday heat; this strongly suggests a system ofphysiologically determined foraging periods (Simpson et alI977b). However, the conditions offloral resource as wellas environmental characteristics external to the flowers (temperature, light intensity, relative humidity) may influence the foraging activity (Schlising 1970;Osmar 1982).But closeness between resource presentation and the activity pattern may not always berealised (Willson and Bertin 1979;Willson et al 1979). The environmental parameter temperature seems to be the major factor controlling the activity patterns. The restricted bee activity at high altitudes is attributable to the prevailing low temperatures. The foraging activity ofpollinator of temperate regions is limited by the characteristic low temperature because the insects have to spend metabolic energy for endogenous heat production (Heinrich 1974).That is why bumble bees capable of endothermic heat regulation fare well in temperates (Janzen 1975).Tropical studies reveal that bees are intolerant ofhigh temperature that is reached around midday (Hedegart 1976;Reddi 1981;Reddi and Subba Reddi 1983). Moreover, it is not advantageous for these insects to work at such hot hours because they lose more water than they gain by visiting flowers for fluids (Janzen 1967). Species foraging during day time exhibit distinct periodicity patterns (Subba Reddi et al 1983). But no such distinct periodicity specific to each species was observed by Ehrenfeld (1979) on Chamaesyce a sub-genus of Euphorbia. Even the matinal bees which forage for briefperiods exhibit distinct periodicities as is evident from the three species ofMelandrena foraging.for pollen on Oenotheradentata in the Mojave desert in California (Linsley et alI955).

8. Pollinator fidelity/flower constancy

Flower constancy of bees was reviewed by Grant (1950)and Free (1963, 1970b). It is only a relative term (excepting monolectic bees). Since individual foragers of the same species exhibit widely varying degrees of fidelity it is not an inherent character of a forager but more likely a consequence ofhabituation during a foray and the diversity and spatial distribution offloral elements in the local plant community (Macior 1974a, 1982).So the primary determinants offlower choice appear to be the amount, quality, and availability of nectar and pollen (Hobbs 1962; Heinrich 1976a,b; Inouye 1978). Plants with many flowers are more attractive to pollinators than those with fewer flowers (Willson and Price 1977;Silander and Primack 1978;Willson and Bertin 1979; Schaffer and Schaffer 1979; Davis 1981; Pyke 1981). Forager density is linearly and .positively related to density offlowers (Waddington 1976). But. the number offlowers does not seem to be a factor in attracting bees in neotropics (Heithus 1979a). The laboratory experiments of Heinrich et al (1977) suggest that bumble bees, once conditioned, are relatively 'constant' foragers despite changes in resource availability. The more recent experimental study of Wells and Wells (1983) using honey bees and artificial flowers supported the individual constancy model. Solitary bees usually do not visit a great range of different flowers and often have preferences for pollen from specific plants (Linsley 1958; Bhoart 1972; Cruden 1972). Consumer switching 380 C Subba Reddi and E U B Reddi behaviour is advantageous because foraging, demands different skills at different flowers and the learning ofthese skills are costly in terms of time and energy (Heinrich 1975d, 1976a).Flexibility in foraging behaviour is essential in order to exploit new food resources as and when they become available (Macior 1968). However, an increase in pollinator constancy to a given plant species retards the elimination ofthe rarer species (Levin and Anderson 1970).

9. Feeding specialisation

Bees are broadly divided into specialists and generalists based on their feeding behaviour. Some species which collect pollen from a few related flowers in the same genus (or even a single species)are called 'oligolectic' (or monolectic);while those which collect pollen from many different and unrelated kinds of blossoms and are called 'broadly polylectic' (Linsley 1958;Michener 1979). These are the 'super specialists' and 'super generalists' respectively of Moldenke (1975). Such a classification received serious criticism from Michener (1979), Eickwort and Ginsberg (1979), Heithaus (1979b), Faegri and Pijl (1979), Moldenke (1979). There is no such thing as a true theoretical generalist feeder or theoretical specialist. This classification fails to express the continuous range of specialization and the flexibility existing within the species. Feeding specialization ofa species may vary from site to site or within sites at different times ofthe year depending on the resource availability and the degree ofcompetitive pressures. As Schoener (1972) and Cody (1974) expressed, it is the overall climatic characteristics which determine plant phenology and structure, which in tum limit and define the emphasis ofdifferent strategies ofresource utilization. Even oligolectic bees can become generalists during periods of low pollen availability (Stephen et al1969; Levin and Anderson 1970;Cruden 1972;Oster and Heinrich 1976)and polylectic bees can become more specialised when conditions favour monopolization of a few resources (Sakagami and Fukuda 1973; Levin 1978).Feeding specialization is greater where the number of potential competing species is higher (Michener 1974, 1979; Heithaus 1979b). Oligolecty or specialist feeding behaviour is more successful and is a prevalent feeding technique in temperate areas, whereas in tropics feeding generalists are prevalent and successful (Linsley 1958; Michener 1954, 1979; Heithaus 1979b). Most tropical bees are not oligolectic probably because they (social bees) are long lived and multivoItine, having therefore to change from one plant to another through the course ofthe year (Heinrich and Raven 1972).Most ofthe flowering species in the tropics are not in bloom for as long as the flight period of most bees, so that oligolecty is often impracticable (Michener 1979). Tropical bees are not only lessspecialised in the feeding strategy but are also less in diversity compared to temperate areas for which the foraging and competitive ability of the highly social bees is attributed (Linsley 1958; Michener 1974, 1979; Heithaus 1979c; Roubik 1979).

10. Genetic consequences of foraging behaviour

The extent of geitonogamy or xenogamy to be realised are dependent on the flight patterns of the bees and the number of open flowers on a plant (Bowers 1975). Bee-flower interactions 381

Moreover, the frequency of hybridization will be an inverse function of flower specialization and constancy, since both constrain the wanderings of pollinators. The probability ofinterspecific pollination is greater when patch size is relatively small and composed of resources which are unpredictable in time, and when neighbouring patches have similar nutritional values. As floral resources diminish through time, search area of the bees increases. Theft of floral resources (flower robbing) by certain visitors may have similar effect (Heinrich and Raven 1972; Cazier and Linsley 1974), and they are likely to promote outcrossing by depleting local pollen and nectar, thus increasing the foraging range and flower visitation rates ofactual pollinators (Roubik 1979). Itfollows, therefore, that the chances for outcrossing may increase by virtue ofan increased search effort by the bees (Frankie 1976). Various foraging behaviours of bees responsible for the recorded inter-tree movement or otherwise were well reviewed by Frankie and Baker (1974), Frankie (1976), Frankie et al (1976), Levin (1978, 1979) and Antonovics and Levin (1980). Two types of foragers, the 'trapliners' and 'opportunists', are recognised basing on their flight ranges and foraging behaviour. (Janzen 1971). The trap liners are usually the large bodied bees such as Euplusia, Eulaema, Euglossa, Centris, Bombus, Xylocopa exhibiting long distance flights, often covering 20 to 30 km and promoting cross-pollination, especially, in the very low density tropical plant populations (Janzen 1971, 1975; Frankie 1975). The plants adapted to receive their service have prolonged flowering period; producing very few flowers each day (Frankie et al1974; Frankie 1975). These bees repeat specific foraging paths. The 'opportunists' are the smaller, often social bees in the low land tropical forests. They normally from flower to flower on the same plant (Baker 1973).The plants adapted to attract such bees exhibit Gentry's (1974) 'big bang flowering' i.e.; produce large and conspicuous flower crop. As a result of their short distance flights they mostly promote autogamy or geitonogamy; sometimes they may fail to mediate pollination, especially, in self-incompatible or dioecious trees. Various kinds of intra- and inter-specific interactions among flower visitors generated inter-tree movement of actual pollinators. Territorial behaviour in bees is one such interaction well known and has been documented in several families (Rozen 1958, 1970; Linsley and Hurd 1959; Cruden 1966; Janzen 1966; Stephen et al 1969; Throp 1969; Frankie 1976; Eickwort 1977; Batra 1978; Frankie and Coville 1979; Michener 1979). In Costa Rica, this behaviour is often observed in the males ofcertain Anthophoridae, Xylocopidae, and in the tribe Euglossine of the Apidae (Dodson and Frymire 1961; Janzen 1964; Frankie and Baker 1974; Frankie 1976; Frankie et al1976; Ardetti 1979; Frankie et al 1979). A given territorial site is usually reoccupied daily during the tree's flowering period (Janzen 1975; Frankie 1976). When intruders are encountered in these defended areas, they are almost chased by the territorial males. Usually this results in displacement of the portion of the tree but in some cases the 'intruder' may be sufficiently disturbed such that it leaves the tree entirely (Frankie and Baker 1974). Effectiveness ofterritorial encounters in displacing potential pollen vector to adjacent conspecific plants enhances outcrossing. Some species ofthe Anthophorid bees (Gaesischia exul, Centris adani, C. aethyctera) are known to forage in close aggregations over the crown of several dry forest tree species in Costa Rica (Frankie and Baker 1974; Frankieet al1976; Frankie 1976). Large crown size and profuse flowering for relatively shorter periods are important factors in determining the occurrence, number and size of aggregations (Frankie 1976). The aggregations move quickly and continuously from one cluster of flowers to another. 382 C Subba Reddi and E U B Reddi

The movement takes the form ofa smooth flowering wave in which there is a rather rapid dissipation in numbers from one flowering branchlet to another. The general stir caused by these groups as they move over the tree surface in 'waves' may provide impetus for atleast some individuals.ofthe more sensitive bee species to move to other food sources such as neighbouring conspecific trees. In some species,intra- and inter-specific aggressive tendencies are regularly observed during foraging. Johnson and Hubbell (1974, 1975) reported aggressive foraging behaviour by stingless bees. Morse (1978)observed interspecific aggression ofbumble bee workers on roses. Displacement ofstingless bees by honey bees from some of the flower species was observed by Roubik (1978). In these aggressions mostly males may butt other insects or pull them off flowers (Alcock et al1977). This tendency is often expressed in the form ofone-on-one attacks or 'bumps' as described by Frankie (1976). When aggressions occur the attacked individual usually moves to another flower on the same plant. However, in some instances the bumped individual is hit with such force that it appears to leave the tree entirely.

11. Biocoenosis relations

Baker (1963)pointed out the need to consider pollination on a community basis. It has been shown that completely interdependent relationships like those of Ficus, Yucca, Pyrrhopappus are exceptions to the non-synchroneity of the life-times of pollinators and flowering oftheir food plants. Normally the pollinators may need more than one plant for feeding and the plants are exposed to more than one pollinator during their flowering time. Itis then important thata constantenergy flowthrough the community has to be maintained at a minimum levelto maintain the pollinatorcommunity (Faegri and PijI1979). Baker et al (1971)discussed the pollination biology ofCeiba acuminata in relation to its community function. Heithaus (1974)and Frankie (1976)showed how important the pollinator-flower interactions are to determining the respective com­ munity structureand to keeping up their integrity. The ability ofsuch bees,judged to be irrelevant in pollination, to obtain food from such plants particularly during unfavourable periods is important in keeping them available in the ecosystem until the appropriate season arrives for the flowers that require them. Froma study offourplant communities in British Columbia, Pojar (1974) clearly showed how bumble bee population is maintained on six different anemophiles which do not benefit from the bees. So to recall the words ofMacior (1974a)"it is imperative thatstudies ofparticular pollination mechanisms be based upon critical observations not only of the mechan­ isms themselves but of the entire ecological context in which they operate".

12. Conservation and management of wild bees

As expressed by Free (1972),intensification ofland utilization and clean cultivation has played havoc with the nesting sites ofwild bees. The extensivecultivation ofsingle crops (Monoculture) in certain areas needed larger pollinator populations for short periods only, outside which no forage is available to pollinators (Free 1972, 1980; Martin and McGregor 1973). The use of herbicides and other weed-controlling practices further reduce bee pasturage/forage (Kevan 1975a).Indiscriminateandexcessiveapplication of Bee-flower interactions 383 insecticides is another factor in reducing the bee populations (Free 1970a, 1972;Martin and McGregor 1973;Kevan 1974,1975a,b; McGregor 1976;Deodikar 1980;Wilson et aI1980). Poisonous effects of herbicides on bees were reported by Anderson and Atkins (1968), Moffett et al (1972). The pesticide poisoning sensitivity was shown to be influenced by pollen feeding conditions (Wahl and Vim 1983). Application ofinsecticides selectivelyand carefully during bees non-foraging timings of that particular crop, provision of continuous supply of bloom (bee pasturage) throughout the season by way of introducing and encouraging the good nectar and pollen yielding plants (including the weeds),plantation ofhollow-pithy stemmed plants around agricultural fieldsand in waste lands which form the nests for some varieties of wild bees, are some ofthe important measures to adopt to conserve the bee pollinators. The non-gregariousness and the unpredictable seasonal availability largely discredi­ ted the wild bees as pollinators (Free 1970a; McGregor 1976;Kapil and Jain 1980).It has long been a general notion that honey bees and other social bees alone can adequately pollinate crops and there is no need for wild bees. Since there is no adequate work on the economic value of wild bees, Parker and Torchio (1989)considered such notion as a premature statement. Nevertheless, over the two decades Megachile pacifica (Leafcutter bees)and N omia melanderi (Alkali bees) for alfalfa and Osmia cornifrons for apples have been successfully managed for (Bohart 1972;McGregor 1976; Kapil and Jain 1980). To have a clear picture ofthe potential ofthe bees to contribute to India's economy through pollination, field surveys of bees species and which species visits which plant species should be immediately undertaken. Then basic research as the nesting behaviour, life histories, communication, nutritional requirement, resource utilization patterns, competitive behaviour, pesticide hazards, their parasites and predators may be taken up. On the plants side also qualitative and quantitative data on floral reward, breeding structure and floral behaviour are urgently needed. Such knowledge is fundamental to developing the techniques towards managing the bees for pollination service.

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