Ovoviviparity

Ovoviviparity occurs in all Blaberidae except the viviparous Diploptera punctata, and in four genera of Blat-tellidae: Sliferia, Pseudobalta (Pseudophyllodromiinae) (Roth, 1989a, 1996), Stayella, and Pseudoanaplectinia (Blattellinae) (Roth, 1984,1995c). As in oviparous cockroaches, type A ovoviviparous species extrude the ootheca as it is being formed. When oviposition is complete, however, the egg case is retracted back into the body and incubated internally in a type of uterus, the brood sac, throughout development. The brood sac is an elaboration of the membrane found below the laterosternal shelf in oviparous cockroaches and is capable of enormous distension during gestation (Fig. 6.14). The eggs have sufficient yolk, but must absorb water from the female to complete development. At hatch, the nymphs are expelled from this maternal brood chamber, and quickly shed their embryonic cuticle. There is some evidence that pressure exerted by the female on the ootheca during extrusion supplies the hatching stimulus (Nutting, 1953a).

Ovoviviparous females are thought to provide only water and protection to embryos during gestation, with the yolk serving as the main source of energy and nutrients. This is supported by data indicating that in ovoviviparous Rhyparobia maderae and Nauphoeta cinerea, water content increases and dry weight decreases during embryogenesis, just as it does in oviparous P. americana (Roth and Willis, 1955c; Roth, 1970a). Even if it is not reflected as weight gain, however, ovoviviparous cockroaches may be supplying more than water to their retained embryos. This is suggested by the physiological intimacy of the embryonic and maternal tissues, and the evidence that maternal transfer of materials occurs in oviparous B. germanica. Based on morphological evidence, Snart et al. (1984a, 1984b) suggested that Byrsotria fumigata and Gromphadorhina portentosa, two Blaberidae commonly considered ovoviviparous, should in fact be classified as viviparous. The surface of the brood sac in these two cockroaches is covered with numerous, closely packed papillae. Pores in the apical region of each papilla exude material thought to result from secretory activity of the brood sac, and the brood sac wall has ultrastructural features characteristic of insect integumentary glands. These authors suggest that the brood sac in these two ovovivip-arous cockroaches is sufficiently similar to that of the viviparous D. punctata to make it likely that the brood sacs of all three function in the same manner. Depriving female Byr. fumigata and G. portentosa of food and water resulted in smaller nymphs, but the relative effects of food and water deprivation are unknown. Recent behavioral observations of G. portentosa indicate that the brood sac indeed may be producing secretions that serve as nutrition to young cockroaches; however, the material is expelled and ingested by neonates immediately after hatch instead of while they are embryos developing inside their mother (Chapter 8). Until demonstrated otherwise, then, G. portentosa should be considered ovoviviparous, with post-hatch parental feeding.

Four genera of Blaberidae, Macropanesthia, Geoscaph-eus, Neogeoscapheus, and Parapanesthia (Rugg and Rose, 1984b, 1984c), are classified as ovoviviparous type B and deposit their eggs directly into the brood sac, where they form a jumbled mass (Fig. 7.5B) rather than the two rows

Fig. 7.5 Oothecae of two Panesthiinae. (A) Thin, membranous, incomplete oothecal case of Panesthia cribrata (ovovi-viparity A). (B) Massed eggs of Geoscapheus dilatatus, a species that lacks an oothecal case (ovoviviparity B). Photos courtesy of Harley Rose.

typical of other cockroaches (Fig. 7.5A). These are the only cockroach taxa known to deposit eggs without forming an ootheca. Some species in the same subfamily (Panesthia australis, Pane. cribrata) exhibit an apparent intermediate stage, where some eggs occur in parallel rows within an incomplete oothecal membrane, while others are applied haphazardly to its outer surface as the ootheca is retracted. In Pane. australis, 90% of examined oothecae had eggs externally attached to the egg case (Rugg and Rose, 1984b, 1984c; D. Rugg, pers. comm. to CAN).

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