Pattern of bacteriocyte formation in Periplaneta americana (L.) (Blattaria: Blattidae)

In the embryos of Periplaneta americana (L.) (Blattaria: Blattidae), bacterial symbionts, together with vitellophages, form a mycetomic structure inside the deutoplasm; this regresses between the 15th and 16th day after deposition of the ootheca. In this article we describe the migration of bacteria across the wall of the midgut from the mycetome, and the topographic distribution of pre-bacteriocyte cells. We also report that the pre-bacteriocytes are present only on the lateral surface of the internal abdominal fat bodies. We discuss the possible embryological origin and evolution of these cells, and put forward the hypothesis that pre-bacteriocytes are derived from oenocytes activated to perform phagocytosis.