Behavioral and Morphological Studies of the Membranous Tergal Structure of Male Blattella germanica (Blattodea: Ectobiidae) During Courtship.

The male German cockroach Blattella germanica (L.) exhibits a characteristic courtship display by raising its wings, turning around, and exposing its tergal glands on the seventh and eighth tergites to the female. The male secretes a courtship pheromone from the tergal glands which induces a strong feeding response in the female, facilitating copulation. Upon multiple, detailed microscopic observations of the courtship display, we found that the male markedly expanded the intersegmental area between the sixth and seventh tergites, but deflated this area as soon as it perceived a tactile stimulus on its back by the female, while continuing to raise its wings and exposing the tergal glands. The intersegmental area is composed of two parts: a membranous posterior part of the sixth tergite, and the regular intertergal membrane. The membranous posterior part was found to be crescentic in shape and clearly separated from the intertergal membrane by traverse tongue-shaped plates. Scanning electron microscopic observation revealed that there were many orifices or pores in the membranous crescentic zone, and its morphological structure was clearly different from that of the intertergal membrane. Our observations suggest that the crescentic zone is likely a secretory gland that may play an important role at the beginning of the male courtship display, different from the tergal glands.

Characterization of a new densovirus infecting the German cockroach, Blattella germanica.

A new DNA virus (Parvoviridae: Densovirinae, Densovirus) was isolated and purified from descendants of field-collected German cockroaches, Blattella germanica. Viral DNA and cockroach tissues infected with B. germanica densovirus (BgDNV) were examined by electron microscopy. Virus particles, about 20 nm in diameter, were observed both in the nucleus and in the cytoplasm of infected cells. Virus DNA proved to be a linear molecule of about 1.2 microm in length. BgDNV isolated from infected cockroaches infected successfully and could be maintained in BGE-2, a B. germanica cell line. The complete BgDNV genome was sequenced and analysed. Five open reading frames (ORFs) were detected in the 5335 nt sequence: two ORFS that were on one DNA strand encoded structural capsid proteins (69.7 and 24.8 kDa) and three ORFs that were on the other strand encoded non-structural proteins (60.2, 30.3 and 25.9 kDa). Three putative promoters and polyadenylation signals were identified. Structural analysis of the inverted terminal repeats revealed the presence of extended palindromes. The genome structure of BgDNV was compared with that of other members of the family Parvoviridae; the predicted amino acid sequences were aligned and subjected to phylogenetic analyses.

Hydrocarbon synthesis by enzymatically dissociated oenocytes of the abdominal integument of the German Cockroach, Blattella germanica.

In insects, hydrocarbons waterproof the cuticle, protect the insect from the external environment, and serve as semiochemicals or their metabolic precursors. In the German cockroach, Blattella germanica, hydrocarbons are synthesized by the abdominal integument, but the precise site of biosynthesis is not known. We developed a method for separation of oenocytes from other cells in the abdominal integument using enzymatic dissociation followed by Percoll gradient centrifugation. Radiolabeled propionate was then used to monitor de novo synthesis of hydrocarbons by dissociated cells. Oenocyte-enriched cell suspensions of abdominal sternites synthesized hydrocarbons, whereas suspensions enriched with epidermal cells did not. Our results show conclusively that hydrocarbons are produced by oenocytes not only in insects whose oenocytes are localized within the hemocoel, but also in those insects whose oenocytes are within the abdominal integument. Furthermore, these data support a hemolymph pathway for transport and delivery of hydrocarbons to both external and internal tissues, including the epicuticle, fat body, and ovaries.

Cysteine proprotease colocalizes with vitellogenin in compound granules of the cockroach fat body.

A cysteine proprotease has been identified in developing embryos of the cockroach Blattella germanica and found to be a maternally encoded gene product that is transferred endocytically to the oocyte. The present study aims at establishing how this maternally derived proprotease is synthesized, packaged, and secreted during vitellogenesis. To this end, proprotease was localized immunocytochemically in the fat body of postmating females and its localization compared with that of vitellogenin over the same developmental periods. Fat bodies in cockroaches are comprised of two different cell types: trophocytes and bacteriocytes. Data show that proprotease and vitellogenin come to colocalize in compound granules of the fat body trophocytes. While synthesis of vitellogenin can be traced back to granules resulting from the coalescence of Golgi-derived vesicles in the trophocyte cytoplasm, proprotease appears to be localized predominantly on the cytolysosomes of both trophocytes and bacteriocytes. When probed with an anti-proprotease antiserum, bacteria are also positively labeled, regardless of whether they are segregated inside the cytolysosomes or free in the bacteriocyte cytoplasm. Since vitellogenin and proprotease colocalize within the same cell organelle, it is assumed that Golgi-derived vesicles, which contain vitellogenin, may fuse with cytolysosomes bearing proprotease to yield compound secretory granules. To account for the present observations, the origin and role of proprotease are discussed in relation to the turnover of bacteria in the fat body and to the requirements of endosymbiosis.