Interestingly, if you do a search in Google Scholar (my favorite search tool) the topic of "bee conservation" is pretty scarce prior to 1990. Much attention was paid to the conservation of habitat but not so much to the bees themselves.   

The idea of conservation, preservation, and restoration of pollinators came into its own during the 1990s. Of course, its a hot topic now, with multiple factions vying for money to study it.   

The following was published in 1997 and the references cited are mostly from the same decade  

Bee Conservation and Increasing Osmia spp. in Maine Lowbush Blueberry Fields  
Author(s): Constance S. Stubbs, Francis A. Drummond, Stephanie L. Allard  
Source: Northeastern Naturalist, Vol. 4, No. 3 (1997), pp. 133-144  

LITERATURE CITED:  

BATRA, S. W. T. 1995. Bees and pollination in our changing environment. Apidologie 26: 1-10. 

BUCHMANN, S. L. and G. P. NABHAN. 1996. The Forgotten Pollinators. Island Press, Washington, D. C. 292 pp.  

CORBET, S. A., N. M. SAVILLE, and J. L. OSBORNE. 1995. Farmland as habitat for bumble bees. Pp. 35-46 In A. Matheson (ed.). Forage for Bees in an Agriculture Landscape. IBRA, Cardiff, UK. 75 pp.  

DAY, M. C. 1991. Towards the Conservation of Aculeate Hymenoptera in Europe. Council of Europe Press, Strasbourg, France. 77 pp.  

FRANKIE, G. W. L. NEWSTROM, S. B. VINSON, AND J. F. BARTHELL. 1993. Nesting-habitat preference of selected Centris bee species in Costa Rican dry forest. Biotropica 25: 322-333. 

FYE, R. E. 1965. Biology of Apoidea taken in trap nests in northwestern Ontario (Hymenoptera). Canadian Entomologist 97: 863-877.  

GATHMANN, A., H. J. GREILER, and T. TSCHARNTKE. 1994. Trap- nesting bees and wasps colonizing set-aside fields: succession and body size, management by cutting and sowing. Oecologia 98: 8-14.  

GREER, S.M., V. J. TEPEDINO, T.L. GRISWOLD, and W. R. BOWLIN. 1995. Pollinator sharing by three sympatric milkvetches, including the endangered species, Astragalus montii. Great Basin Naturalist 55: 19-28. 

GROOMBRIDGE, B. 1993. 1994 IUCN Red List of Threatened Animals. IUCN, Cambridge, England. 286 pp. 

KEVAN, P. G., E. A. CLARK, and V. G. THOMAS. 1990. Insect pollinators and sustainable agriculture. American Journal of Alternative Agriculture 5: 13-22. 

KROMBEIN, K. V. 1967. Trap-nesting Wasps and Bees. Smithsonian Press, Washington, D. C. 570 pp. 

LASALLE, J. AND I. D. GAULD. 1993. Hymenoptera: their diversity, and their impact on the diversity of other organisms.	Pp. 1-26, In J. Lasalle and I. D. Gauld (eds.). Hymenoptera and Biodiversity. CAB International, Wallingford, UK. 348 pp. 

MACIOR, L. W. 1978. Pollination ecology and endemic adaptations of Pedicularis furbishiae S. Wat. Bulletin of the Torrey Botanical Society 105: 268-277. 

MEDLER, J. T. 1967. Biology of Osmia taken in trap Nests in Wisconsin 144	Northeastern Naturalist	Vol. 4, No. 3 (Hymenoptera: Megachilidae). Annals of the Entomological Society of America 60: 338-344. 

NABHAN, G. P. 1996. The parable of the poppy and the bee. The Nature Conservancy 46: 10-15. 

NEFF, J. L. and B. B. SIMPSON.	1993. Bees, pollination systems, and plant diversity. Pp. 143-165, In J. Lasalle and I. D. Gauld. (eds.). Hymenoptera and Biodiversity. CAB International, Wallingford, UK. 348 pp. 

O'TOOLE, C. 1994. Who cares for solitary bees? Pp. 47-56 In A. Matheson (ed.). Forage for Bees in an Agriculture Landscape. IBRA, Cardiff, UK. 75 pp. 

O'TOOLE, C. and A. RAW. 1991. Bees of the World. Blandford Publishing Co, London, UK. 192 pp. 

PIMENTEL, D., H. ACQUAY, M. BILTONEN, P. RICE, M. SILVA, J. NELSON, V. LIPNER, S. GIORDANO, A. HOROWITZ, and M. D'AMORE. 1992. Environmental and economic costs of pesticide use. BioScience 42: 750-761. 

RICHARDS, K. W. 1984. Alfalfa Leafcutter Bee Management in Western Canada. Agriculture Canada Publication 1495, Ottawa, Canada. 53 pp. 

ROUBIK, D. W. 1989. Ecology and Natural History of Tropical Bees. Cambridge University Press, Cambridge, MA. 514 pp. 

SENFT, D. 1990. Protecting endangered plants. Agricultural Research, 38: 16- 18. 

SOLBRIG, O. T. 1991. From Genes to Ecosystems: A research Agenda for Biodiversity. International Union of Biological Science, Paris, France. 116 pp. 

STUBBS, C. S., F. A. DRUMMOND, and E. A. OSGOOD. 1994. Osmia ribifloris	bidermannii	and	Megachile	rotundata	(Hymenoptera: Megachilidae) introduced into the lowbush blueberry agroecosystem in Maine. Journal of the Kansas Entomological Society 67: 173-185. 

STUBBS, C. S., H. A. JACOBSON, E. A. OSGOOD, and F. A. DRUMMOND. 1992. Alternative Forage Plants for Native Bees Associated with Lowbush Blueberry, Vaccinium spp., in Maine. MAES Tech. Bull. 148. University of Maine, Orono, ME. 54 pp. 

TORCHIO, P. F. 1990. Diversification of pollination strategies for U. S. crops. Environmental Entomology 19: 1649-1656. 

UNRUH, T. R. and R. H. MESSING. 1993. Intraspecific biodiversity in the Hymenoptera: implications for conservation and biological control. Pp. 27- 52 In J. Lasalle and I. D. Gauld (eds.). Hymenoptera and Biodiversity. CAB International, Wallingford, UK. 348 pp. 

WESTRICH, P. 1996. Habitat requirements of central European bees and the problems of partial habitats. Pp. 1-16 In A. Matheson, S. L. Buchmann, C. O'Toole, P. Westrich, and I. H. Williams (eds.). The Conservation of Bees. Academic Press Inc. San Diego, CA. 254 pp.

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