the second if you really want a lot of reading:
Alexander, EW (1907). A plurality of queens without perforated zinc. Gleanings in Bee Culture 35(23):1136-1138.
Gleanings in bee culture. v.35 (1907).
1946. Two-queen vs. single-queen colony management. Gleanings Bee Cult. 64(10): 593-596.
1976. Two-queen system of honey bee colony management. 11 p. U.S. Department of Agriculture, Production Research Report 161. Moeller
Alexander, E.W. (1907a). A plurality of queens without perforated zinc. Gleanings in Bee Culture 35(23):1136-1138.
Gleanings in bee culture. v.35 (1907).
Alexander, E.W. (1907b). The plural queen system: all queens but one disappear at the end of the season. Gleanings in Bee Culture 35(17):1496.
Gleanings in bee culture. v.35:no.13-24 (1907:July-Dec.).
Banker, R. (1968). A two queen method used in commercial operations. Apiacta 2, 4 pp.
Banker, R. (1968). A two-queen method used in commercial operations. - Google Search
Banker, R. (1979). Part B. Two-queen colony management. The Hive and the Honey Bee (1975 extensive revision) pp. 404-410, Dadant and Sons Inc., Carthage, Illinois.
Bee (1904). Wells hive and system. West Gippsland Gazette, 17 May 1904, p.4.
WELLS HIVE AND SYSTEM - West Gippsland Gazette (Warragul, Vic. : 1898 - 1930) - 17 May 1904
British Bee-Keepers’ Association Quarterly Converzatione (Thursday March 31, 1892). Mr Wells new method of working bees. The British Bee Journal and Beekeepers’ Record and Adviser 20(510):126, 132-133.
https://ia802508.us.archive.org/29/items/britishbeejourna1892lond/britishbeejourna1892lond.pdf
Butler, C. (1974). The World of the Honeybee. Collins New Naturalist, London; Butler, C. (1962). Transactions of the Royal Entomological Society of London 114(1): 1-29.
Danka, Robert G., and Norman E. Gary. “Estimating foraging populations of honey bees (Hymenoptera: Apidae) from individual colonies.” Journal of economic entomology 80.2 (1987): 544-547.
Donaldson-Matasci, Matina C., Gloria DeGrandi-Hoffman, and Anna Dornhaus. “Bigger is better: honeybee colonies as distributed information-gathering systems.” Animal behaviour 85.3 (2013): 585-592.
Evans, Peter. Advances in Insect Physiology. Vol. 26. Academic Press, 1996. (pages128-135)
Farrar, C.L. (1936). Two-queen vs. single-queen colony management. Gleanings in Bee Culture 64(10):593-596.
Farrar, C.L. (May 1946). Two-queen colony management. United States Department of Agriculture. Agricultural Research Administration. Bureau of Entomology and Plant Quarantine, 14pp.
http://ufdc.ufl.edu/AA00026061/00001/14j
Farrar, CL 1953 Two queen colony management. Bee World 34 (10): 189-194.
Flottum, Kim. “The Backyard Beekeeper’s Honey Handbook: A Guide to Creating, Harvesting, and Baking with Natural Honeys”. Crestline Books, 2009.
Hesbach, W. (2015). Two queens, one hive=lots of honey. Honey Bee Suite
https://honeybeesuite.com/two-queens-one-hivelots-of-honey/
Hesbach, W. (22 February 2016). The horizontal two-queen system. Bee Culture
http://www.beeculture.com/the-horizontal-two-queen-system/ Nabors, R. (1 August 2016). Comparing two-queen colony management methods. American Bee Journal 156(8). Beekeeping topics
http://americanbeejournal.com/comparing-two-queen- colony-management-methods/
Heuvel, B. (March 2013). Running two-queen colonies.
http://www.beesource.com/forums/sho...ning-two-queen-colonies&p=1202508#post1202508
Hogg, J.A. (1983a). Methods for double queening the consolidated broodnest hive: fundamentals of queen introduction. Part 1 The Fundamentals of Queen Introduction. American Bee Journal 123:383-388.
http://www.twilightmd.com/Samples/Hogg/Hogg_Halfcomb___Publications/ABJ_1983_1May.pdf
Hogg, J.A. (1983b). Methods for double queening the consolidated broodnest hive: the fundamentals of queen introduction. Part 2 Conclusion. American Bee Journal 123:450-454.
http://www.twilightmd.com/Samples/Hogg/Hogg_Halfcomb___Publications/ABJ_1983_2June.pdf
Hogg, J.A. (2005). The Juniper Hill plan for comb honey production, improved two-queen system. American Bee Journal 145(2):138-141.
http://www.twilightmd.com/Samples/Hogg/Hogg_Halfcomb___Publications/ABJ_2005_February.pdf
Killion, E.E. (1981). Honey in the Comb. Dadant & Sons. Inc, Carthage, Illinois.
Lensky, Yaacov, and Yossi Slabezki. “The inhibiting effect of the queen bee (Apis mellifera L.) foot-print pheromone on the construction of swarming queen cups.” Journal of Insect Physiology 27.5 (1981): 313-323.
Mark L. Winston. 1987. The Biology of the Honey Bee. Harvard University Press. Cambridge, MA. (pages 90-109)
Moeller, F.E. (April 1976). Two queen system of honeybee colony management. Production Research Report 161, Agricultural Research Service, United States Department of Agriculture, 15pp., Washington DC 20402.
http://naldc.nal.usda.gov/download/CAT87210713/PDF and
http://mesindus.ee/files/52221134-2-queen-management.pdf
Nabors, R. (1 August 2016). Comparing two-queen colony management methods. American Bee Journal 156(8)-. Beekeeping topics
http://americanbeejournal.com/comparing-two-queen-colony-management-methods/
The role of queen mandibular pheromone and colony congestion in honey bee (Apis mellifera L.). Journal of Insect Behavior, 1991, Volume 4, Number 5, Page 649. Mark L. Winston, Heather A. Higo, Simon J. Colley,
Wells, G. (18 May 1893). Comparing the double and single-queen systems. The British Bee Journal and Beekeepers Record and Adviser 21(569):195-196.
Wells, G. (May 10, 1894). British Bee Journal, Bee-Keepers’ Record and Adviser 22:183-184. The Wells System. Reply to Mr Walton’s open letter.
https://ia600200.us.archive.org/3/items/britishbeejourna1884lond/britishbeejourna1884lond.pdf
Zheng, Huo-Qing, et al. “Sustainable multiple queen colonies of honey bees, Apis mellifera ligustica.” Journal of apicultural research 48.4 (2009): 284-289.