Ultrastructural studies of the fat body and bacterial endosymbionts of Cryptocercus punctulatus Scudder (Blattaria: Cryptocercidae)

Transmission electron microscopy of ultra-thin sections and freeze-fracture replicas of the fat body of the wood feeding cockroach Cryptocercus punctulatus show that the protein and lipid stores in trophocytes are substantially smaller than in those of cockroaches that are not xylophagous. The urocytes exhibit needle-shaped deposits of urate arranged in concentric layers around central cores. Bacteriocytes harbor in their cytoplasm Gram-negative bacterial endosymbionts enclosed in a vacuolar membrane. In the vacuolar space, vesicles formed by a blebbing process were observed detaching from the symbionts' outer membrane. These processes suggest the presence of metabolite exchange between host cell and endosymbionts. Among adjacent bacteriocytes, trophocytes, and urocytes, cell membranes exhibit junctional complexes that may allow for metabolic interaction. Transmission of the bacterial endosymbionts occurs via transovarial transmission, as in other cockroaches.