O'Donnell, K., Bacterial Foodborne Pathogens and Mycology Research Unit, National Center for Agricultural Utilization Research, US Department of Agriculture, Agricultural Research Service, 1815 North University Street, Peoria, IL, United States
Sink, S., Bacterial Foodborne Pathogens and Mycology Research Unit, National Center for Agricultural Utilization Research, US Department of Agriculture, Agricultural Research Service, 1815 North University Street, Peoria, IL, United States
Libeskind-Hadas, R., Department of Computer Science, Harvey Mudd College, Claremont, CA, United States
Hulcr, J., School of Forest Resources and Conservation, University of Florida, Gainesville, FL, United States
Kasson, M.T., Division of Plant and Soil Sciences, West Virginia University, Morgantown, WV, United States
Ploetz, R.C., Tropical Research and Education Center, University of Florida, Homestead, FL, United States
Konkol, J.L., Tropical Research and Education Center, University of Florida, Homestead, FL, United States
Ploetz, J.N., Tropical Research and Education Center, University of Florida, Homestead, FL, United States
Carrillo, D., Tropical Research and Education Center, University of Florida, Homestead, FL, United States
Campbell, A., Tropical Research and Education Center, University of Florida, Homestead, FL, United States
Duncan, R.E., Tropical Research and Education Center, University of Florida, Homestead, FL, United States
Liyanage, P.N.H., Tea Research Institute of Sri Lanka, St. Coombs, Talawakelle, Sri Lanka
Eskalen, A., Department of Plant Pathology and Microbiology, University of California, Riverside, CA, United States
Na, F., Department of Plant Pathology and Microbiology, University of California, Riverside, CA, United States
Geiser, D.M., Department of Plant Pathology and Environmental Microbiology, Pennsylvania State University, University Park, PA, United States
Bateman, C., School of Forest Resources and Conservation, University of Florida, Gainesville, FL, United States
Freeman, S., Institute of Plant Protection, ARO, The Volcani Center, Bet Dagan, Israel
Mendel, Z., Institute of Plant Protection, ARO, The Volcani Center, Bet Dagan, Israel
Sharon, M., Institute of Plant Protection, ARO, The Volcani Center, Bet Dagan, Israel
Aoki, T., National Institute of Agrobiological Sciences, Genetic Resources Center, 2-1-3 Kannondai, Tsukuba, Ibaraki, Japan
Cossé, A.A., Crop Bioprotection Research Unit, National Center for Agricultural Utilization Research, US Department of Agriculture, Agricultural Research Service, 1815 North University Street, Peoria, IL, United States
Rooney, A.P., Crop Bioprotection Research Unit, National Center for Agricultural Utilization Research, US Department of Agriculture, Agricultural Research Service, 1815 North University Street, Peoria, IL, United States

The mutualism between xyleborine beetles in the genus Euwallacea (Coleoptera: Curculionidae: Scolytinae) and members of the Ambrosia Fusarium Clade (AFC) represents one of 11 known evolutionary origins of fungiculture by ambrosia beetles. Female Euwallacea beetles transport fusarial symbionts in paired mandibular mycangia from their natal gallery to woody hosts where they are cultivated in galleries as a source of food. Native to Asia, several exotic Euwallacea species were introduced into the United States and Israel within the past two decades and they now threaten urban landscapes, forests and avocado production. To assess species limits and to date the evolutionary diversification of the mutualists, we reconstructed the evolutionary histories of key representatives of the Fusarium and Euwallacea clades using maximum parsimony and maximum likelihood methods. Twelve species-level lineages, termed AF 1-12, were identified within the monophyletic AFC and seven among the Fusarium-farming Euwallacea. Bayesian diversification-time estimates placed the origin of the Euwallacea- Fusarium mutualism near the Oligocene-Miocene boundary ~19-24. Mya. Most Euwallacea spp. appear to be associated with one species of Fusarium, but two species farmed two closely related fusaria. Euwallacea sp. #2 in Miami-Dade County, Florida cultivated Fusarium spp. AF-6 and AF-8 on avocado, and Euwallacea sp. #4 farmed Fusarium ambrosium AF-1 and Fusarium sp. AF-11 on Chinese tea in Sri Lanka. Cophylogenetic analyses indicated that the Euwallacea and Fusarium phylogenies were largely incongruent, apparently due to the beetles switching fusarial symbionts (i.e., host shifts) at least five times during the evolution of this mutualism. Three cospeciation events between Euwallacea and their AFC symbionts were detected, but randomization tests failed to reject the null hypothesis that the putative parallel cladogenesis is a stochastic pattern. Lastly, two collections of Euwallacea sp. #2 from Miami-Dade County, Florida shared an identical cytochrome oxidase subunit 1 (CO1) allele with Euwallacea validus, suggesting introgressive hybridization between these species and/or pseudogenous nature of this marker. Results of the present study highlight the importance of understanding the potential for and frequency of host-switching between Euwallacea and members of the AFC, and that these shifts may bring together more aggressive and virulent combinations of these invasive mutualists. © 2014 .