The Annual Review of Entomology was first published in 1956. In that year, Brooks (13) reported to the Tenth International Congress of Entomology on the nature and significance of the intracellular bacteroids (bacteria-like microorganisms) of the cockroach, Blattella germanica. One very signifi­ cant observation reported was the production of aposymbiotic (bacteroid­ free) cockroaches by "modern" therapeutic means: antibiotics. This observation was significant in two respects. First, the intracellular bac­ teroids revealed their bacteria-like sensitivity to an array of antibiotics. Second, insect hosts could now be examined free of their bacteroid symbi­ otes. It appeared that symbiosis research had entered a new era. It is rather disappointing to report that 25 years later insect-microbial symbiosis research has not, in general, progressed beyond the initial descriptive phase. The existence of an intimate relationship between many insect species and large numbers of intracellular microorganism-like particles has been known for over a century (16). The light-microscopical observations of the pioneer­ ing workers of the nineteenth and early twentieth centuries culminated in the extensive studies of Buchner and his students ( 16) . From these studies,