Primary and Secondary Symbionts, So Similar, Yet So Different Fabrice Vavre and Henk R. Braig Proteobacteria as Primary Endosymbionts of Arthropods Abdelaziz Heddi and Roy Gross The Bacteroidetes Blattabacterium and Sulcia as Primary Endosymbionts of Arthropods M. Montagna, L. Sacchi, N. Lo, E. Clementi, D. Daffonchio, A. Alma, D. Sassera, and C. Bandi Secondary Symbionts of Insects: Acetic Acid Bacteria Elena Crotti, Elena Gonella, Irene Ricci, Emanuela Clementi, Mauro Mandrioli, Luciano Sacchi, Guido Favia, Alberto Alma, Kostas Bourtzis, Ameur Cherif, Claudio Bandi, and Daniele Daffonchio Facultative Tenants from the Enterobacteriaceae within Phloem-Feeding Insects T.L. Wilkinson Stammerula and Other Symbiotic Bacteria within the Fruit Flies Inhabiting Asteraceae Flowerheads Luca Mazzon, Isabel Martinez Sanudo, Claudia Savio, Mauro Simonato, and Andrea Squartini Candidatus Midichloria mitochondrii: Symbiont or Parasite of Tick Mitochondria? D. Pistone, L. Sacchi, N. Lo, S. Epis, M. Pajoro, G. Favia, M. Mandrioli, C. Bandi, and D. Sassera Rickettsiella, Intracellular Pathogens of Arthropods Didier Bouchon, Richard Cordaux, and Pierre Greve Arthropods Shopping for Wolbachia Daniela Schneider, Wolfgang J. Miller, and Markus Riegler Host and Symbiont Adaptations Provide Tolerance to Beneficial Microbes: Sodalis and Wigglesworthia Symbioses in Tsetse Flies Brian L. Weiss, Jingwen Wang, Geoffrey M. Attardo, and Serap Aksoy Rickettsia Get Around Yuval Gottlieb, Steve J. Perlman, Elad Chiel, and Einat Zchori-Fein Cardinium: The Next Addition to the Family of Reproductive Parasites J.A.J. Breeuwer, V.I.D. Ros, and T.V.M. Groot The Genus Arsenophonus Timothy E. Wilkes, Olivier Duron, Alistair C. Darby, Vaclav Hypsa, Eva Novakova, and Gregory D. D. Hurst Index