Perhaps no aspect of cockroach biology has been studied as extensively as the range of mechanisms by which they replenish the earth. Understandably so, given that their variation in this arena is a rich source of comparative material and that reproduction in many species is amenable to laboratory study. Several reviews of cockroach reproduction are available, including Roth and Willis (1954b, 1958a), Roth (1970a, 1974a), and Bell and Adiyodi (1982b), among others.
In the majority of cockroaches, reproduction is characterized by the formation of an ootheca: eggs are released from the ovaries, move down the oviducts, are oriented into two rows by the ovipositor valves, then surrounded by a protective covering. Three general reproductive categories are recognized, with two of these broken into subcategories (Table 7.1) (Roth, 1989a, 1991a, 2003c; Roth and Willis, 1954b, 1958a). In oviparity type A, females drop the egg case shortly after formation. In oviparity type B, females carry the ootheca externally throughout embryonic gestation, then drop it immediately prior to hatch; eggs also may hatch while the ootheca is attached to the mother. Ovoviviparous females gestate eggs internally, but the embryos rely primarily on yolk nutrients to fuel and support development. In category A ovoviviparous females, the ootheca is first extruded, as in oviparous taxa, but it remains attached and is retracted a short time later into a brood sac. When the nymphs are ready to hatch, the ootheca is fully extruded and the neonates emerge from their embryonic membranes. The eggs are deposited directly from the oviducts into the brood sac in ovoviviparous type B species; there is no oothecal case. In viviparous forms, oviposition is similar to the ovoviviparous type A cockroaches, but the embryos are nourished within the brood sac on a proteinaceous fluid secreted by the mother.
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