Through Dr. Rozen's worldwide research on the biology, immature stages, and evolutionary relationships of bees (Hymenoptera: Apoidea), the AMNH houses what is believed to be the most complete collection of bee eggs, larvae, and pupae.  Since 1949, Dr. Rozen has conducted fieldwork in the United States, Europe, Trinidad, Republic of South Africa, Namibia, Egypt, Morocco, Turkey, Brazil, Chile, Venezuela, Israel, Pakistan, Mexico, Argentina, Peru, and the former Soviet Republic of Kyrgyzstan. Dr. Rozen has focused on the comparative biology and systematics of solitary and cleptoparasitic taxa.  He is currently working on a research project with Dr. Isabel Alves-dos-Santo of the University of São Paulo and Dr. Gabriel Melo of the Universidade Federal do Paraná, Curitiba, on Brazilian solitary and cleptoparasitic bees.  With Prof. Hikmet Özbek of Atatürk University, Erzurum, Turkey, he is examining the immature stages of rophitine bees worldwide, and with Dr. Soliman M. Kamel, Suez Canal University, Ismailia, Egypt, he is studying the evolutionary relationships of the parasitic bee genus Radoszkowskiana with Megachile and Coelioxys.  The results of his research have been reported in more than 120 research papers.