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2. Mesquida, J., Renard, M.: ibid.20, 197 (1989)
3. Parker, F. D., Hatley, C. L., in: Proc. 4th Int. Syrup. on Pollination (D. M. Caron, ed.). College Park: Md. Agric. Exp. Sta. Spec. Misc. Pub]. 1 (1979)
4. Heinrich, B.: Bumblebee Economics. Cambridge: Harvard Univ. Press 1979; Winston, M. L.: The Biology of the Honey Bee. Cambridge: Harvard Univ. Press 1987; Roubik, D. W.: Ecology and Natural History of Tropical Bees. Cambridge: Cambridge Univ. Press 1989
5. Danka, R. G., Villa, J. D., Gary, N. E.: BeeScience3, 16 (1993)