Cockroache; Ecology, behavior & history - W.J. Bell

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 ovoviviparous
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, Geoscapheus,
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 (ovoviviparity
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).
VIVIPARITY
Diploptera punctata is the only known viviparous species
of cockroach. Its ootheca contains about a dozen small
eggs and has an incomplete oothecal membrane (Roth
and Hahn, 1964). Initially the eggs lack sufficient yolk and
water to complete development (Roth and Willis, 1955a),
but embryos ingest water and nutritive material synthesized
and transported by the walls of the brood sac at a
rate paralleling embryonic growth (Stay and Coop, 1973,
1974; Ingram et al., 1977). The brood sac “milk” is composed
of about 45% protein, 5% free amino acids, 25%
carbohydrates, and 16–22% lipids. The milk proteins are
encoded by a multigene family that arose via the modification
of genes preexisting in ovoviviparous species
(Williford et al., 2004). Embryos begin oral intake of the
milk just after closure of their dorsal body wall and continue
until shortly before partition. The ultimate source
of nutrition for the embryos is the food intake of the
mother; females normally double their body weight during
gestation, and the embryos of starved females die.
Diploptera nymphs are large and well developed when
they emerge, requiring fewer molts to adulthood than any
studied cockroach. Egg fresh weight increases more than
73 times during gestation (Table 7.2) (Roth and Willis,
1955a), while the fresh weight of the ovoviviparous
species N. cinerea doubles. In the latter, the weight increase
is correlated solely with the absorption of water;
solids are slowly lost until partition (Roth and Willis,
1955c). Neonates of D. punctata are at least twice the size
of those of N. cinerea (see Fig. 3 in Roth and Hahn, 1964),
yet adults of the latter are considerably larger than fieldcollected
adults of D. punctata (approximately 27 mm
and 17 mm in length, respectively—Cochran, 1983a;
WJB, unpubl. data). Diploptera females have three or four
post-embryonic instars, compared with the usual seven
to 13 in a sample of 11 other species of Blattaria (Willis et
al., 1958). This suggests that D. punctata completes a substantial
proportion of its juvenile development as an embryo,
with a corresponding decrease in the duration of
post-embryonic development. During embryogenesis,
120 COCKROACHES