Jean-Marie, The best reference I know of relating to your query is a publication issued by the USDA in 1976 entitled "Insect Pollination of Cultivated Plants" by S.E. McGregor. Agriculture Handbook No. 496 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock No. 001-000-03549-5 Hope this is of some help. mac