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Palynological analysis of food reservesfound in a nest of Bombus atratus (Hym.Apidae)Maria C. Telleria aa CONICET, Cátedra de Palinología, Facultad de Ciencias Naturales deLa Plata, Universidad Nacional de La Plata, Paseo del Bosque, 1900, LaPlata, Argentina

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To cite this article: Maria C. Telleria (1998): Palynological analysis of food reserves found in a nest ofBombus atratus (Hym. Apidae), Grana, 37:2, 125-127

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Grana 37: 125-127, 1998

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Palynological analysis of food reserves found in a nest ofBombus atratus (Hym. Apidae)

MARIA C. TELLERIA

Telleria M. C Palynological analysis of food reserves found in a nest οf Bombus atratus (Hym. Apidae).- Grana 37: 125-127. ISSN 0017-3134.

The pollen present in food reserves, pollen masses and honey, stored in an aerial nest of Bombusatratus was investigated. Field observations were also made. 23 pollen morphological types, belongingto 16 families of plants, were identified. The principal sources of nectar were: Eucalyptus spp., Apteniacordifolia, Lagerstroemia indica and Salvia microphylla. While Solarium spp. and Liliaceae, were themain sources of pollen. These analyses of pollen reserves and honey, coupled with field observations,allow a reconstruction of the wide foraging spectrum of Bombus atratus.

María C. Tellería, CONICET, Cátedra de Palinología, Facultad de Ciencias Naturales de La Plata,Universidad Nacional de La Plata, Paseo del Bosque, 1900 La Plata, Argentina.

(Manuscript accepted 15 July 1998)

Bumble bees {Bombus Latr.) are active pollinators, which bybuzz foraging can collect from flowers which are inaccessibleto honey bees. This prowess in pollen harvesting has led toan attempt to domesticate and use these insects in order toimprove the pollination of profitable crops (Free 1970,Pouvreau 1984).

Bumble bees have a complex social life, they live in annualcolonies (Roubik 1992) and build underground or aerialnests which are made up of an almost flat cluster or roundishwax cells. After the offspring leave, the cells become foodstores. Pollen loads are stored and pressed into some cells;nectar, turned into honey, is kept in other cells (Pouvreau1984).

Knowledge of the flowers visited by Bombus spp. comesmainly from field surveys (Harder 1985, Ricciardelli 1986,1988, 1990) and pollen analysis of corbicular loads. (Free1970, Bolchi Serini 1992). Liu et al. (1975) conducted furtherresearch on corbicular loads of pollen, and larval meconiafound in five nests of four Bombus species from Canada.Brizuela et al. (1993) studied the foraging behaviour ofBombus atratus in Macroptilium bracteatum flowers.

According to Free (1970) a study only of the pollenadhering to bumble bees or stored in their nest underestimatestheir floral preferences. Pouvreau (1984), however, considersthe analysis of pollen reserves to be significant, although heclaims that such a study does not yield any informationabout nectar harvesting. So far there is a lack of knowledgeabout honeys produced by bumble bees.

This preliminary study was performed in order to evaluatethe contribution of pollen analysis of the food reserves(pollen masses and honey), in studying the foraging behavi-our of Bombus atratus Lep.

Bombus atratus is a Neotropical species (Roubik 1992)which belongs to the Pampean region entomofauna. It lives

in farming ecosystems and urban areas (Lie. Abramovich1994: pers. comm.).

MATERIALS AND METHODS

The nest under study was found under some boards in the gardenof a house in the city of La Plata, Argentina, in January 1996.Cultivated plants (most ornamentals) dominate in the surroundingsalthough patches of spontaneous vegetation are still present.

Bumble bees were observed around the nest during that monthand attention was paid to the flowers they visited most. At thebeginning of February, the whole nest was removed and the feedingreserves were carefully harvested by means of a small spoon. 15 gof pollen and 78 g of honey were collected from 197 cells. The honeywas treated according to Louveaux et al. (1978). The pollen masswas first dis-segregated with a glass rod in 200 ml of distilled waterat 80-90°C, and then with a magnetic stirrer for 15-20 minutes.From this mixture, 5 ml was centrifuged. After removing the super-natant, the sediment was dehydrated and acetolysized. Specimens ofunacetolysized pollen were made to see whether honeydew elementswere present. The determination of the pollen types was based onreference pollen specimens from flowers collected in gardens andvacant plots around the nest. Pollen counts of both honey andpollen reserves were made to a total of 1200 grains (Vergeron 1964),using five slides in each case.

RESULTS AND DISCUSSION

The microscope observation of the food reserves revealedthat Bombus atratus is a generalist, like most of the Bombusspecies studied (Free 1970, Liu et al. 1975, Buchmannn 1983,Pouvreau 1984, Harder 1985, Ricciardelli 1986, 1988, 1990;Bolchi Serini 1992) and exhibits a diverse harvesting range.The analyses also confirm that a few of the plants speciesvisited by B. atratus provide both nectar and pollen at thesame time (Table I), as has been mentioned by Liu et al.(1975) and Buchmann (1983).

ι 1998 Scandinavian University Press. ISSN 0017-3134 Grana 37 (1998)

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126 M. C. Telleria

Table I. Pollen identified in food reserves of Bombus atratus

grouped by family.

Taxa Honey Pollen

AlZOACEAE

Aptenia coridifoliaASTERACEAE

Ambrosia spp.AnthemidaeCarduus spp.Cenlaurea spp.Cichorium intybusCirsium vulgäre

BlGNONIACEAE

Campsis radicansCAPRIFOLIACEAE

Lonicera caprifoliaCONVOLVULACEAE

Ipomoea spp.CuCURBITACEAE

Cucurbita spp.CYPERACEAE

DlPSACACEAE

Dipsacus sativusFABACEAE

Acacia spp.LAMIACEAE

Šalvia spp.Teucrium spp.

LlLIACEAE

Cordyline australisLYTHRACEAE

Lagerstroemia indicaMYRTACEAE

Eucalyptus spp.OLEACEAE

Ligustrum spp.RHAMNACEAE

SOLANACEAE

Solarium spp.Unknown pollen

PPPPP

P

P

PP

P

P

PPPP

12

43

PP

27

5.5

38.54.5

5.5

30P

P=polien whose frequency is less than 1%.

Plants visited to collect nectar. - According to the rangeof pollen types in the honey, the bumble bees intensivelyforaged only a few plants: Eucalyptus spp., Lagerstroemiaindica and Aptenia coridifolia, but they foraged a wide varietyof plants superficially: Acacia spp., Anthemidae, Campsisradicans, Carduus spp., Centaurea spp., Cichorium intybus,Cirsium vulgäre, Cordyline vulgaris, Cucurbita spp., Ĺoniceracaprifolia, Ipomoea spp., Dipsacus sativus, Acacia spp., Šalviamicrophylla, Teucrium spp., Liliaceae, Ligustrum spp. andRhamnaceae (Table 1). The presence of pollen from non-nectariferous Solarium in the honey, may be a contaminationproduced inside the nest, such as also occurs in the hive ofhoneybees (Louveaux 1968).

The harvesting behaviour of B. atratus, is similar to thatof other honey producing insects suchs as honeybees andwasps (Costa de Bringas 1986, Telleria 1996). In this wayhymenopterous Bombus bees also save energy (Waddington& Holden 1979) since most of the plants visited were closeto the nest.

Intense activity was observed on Šalvia microphylla flowers,

which were located a few metres from the nest, althoughpollen of this species was scarcely represented in the honey.A similar fact was registred in Šalvia honeys produced byhoneybees (Louveaux et al. 1978). This might be due to thefloral mechanism of Šalvia, whose pollen is unloaded in anototribic way when the insect inserts its prosboscis to reachthe nectary (Faegri & van der Pijl 1979). This mechanism ofpollen unloading was also observed while B. atratus wasforaging nectar from Macroptilium bracteatum (Brizuelaet al. 1993).

Plants visited to collect pollen. - The presence of largequantities of just a few pollen types in the pollen massesshowed a preferential utilization of the available floweringplants. Liliaceae and the buzz-pollinated Solanum (probablyS. granulosum leprosum which was abundant in vacant landand frequently visited) were the main sources of pollen. Theless significant pollen sources were Aptenia cordifolia,Ambrosia spp., Campsis radicans, Cordyline australis andLagerstroemia indica (Table I) . The restricted variety ofpollen resources foraged by B. atratus in relation to thenectariferous ones, has already been noted in other Bombusspecies in Canada by means of meconia analysis. This facthas given rise to the idea that pollen harvesting behaviourmight have evolved separately from nectar harvesting behavi-our (Liu et al. 1975).

Honey versus pollen. - The comparative analysis of foodreserves (Table I) , confirms statements by Free (1970) andPouvreau (1984) that analysis of the stored pollen is notsufficient in itself to demonstrate the plants most visited byBombus. Pollen analysis of the honey, coupled with fieldsurveys gives a larger foraging spectrum of the plants visitedfor nectar. Together these indicate a wider harvesting range.The biggest drawback to the study of honey from B. atratusis its collection from nests which are usually found under-ground in farming ecosystems.

ACKNOWLEDGEMENTS

The author wishes to thank Lie. Alberto Abramovich for determiningthe insects, and Lic. Juan C. Gamerro for reading the manuscript.

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