Studies of many new mollicutes isolates from insects collected over the last 2 years have suggested a tentative grouping of host-parasite relationships. Those that have been partially studied to date include: 1) temporary gut infection or gut contamination in which the spiroplasmas may survive gut passage with little or no multiplication and with very limited persistence; 2) permanent gut infection in which the host gut is the year-round reservoir; 3) gut infection with hemolymph invasion in which spiroplasmas occur commonly in insect guts but with ability to invade the hemolymph of certain species to which they are pathogenic; and 4) hemolymph infection with noncultivable spiroplasmas in which spiroplasmas occurring in hemolymph or other host tissues are noncultivable.