Oviparity

Oviparous type A cockroach species characteristically produce an ootheca, a double row of eggs completely enclosed by a protective outer shell (Stay, 1962; Roth, 1968a). A raised

Table 7.1. Modes of reproduction in cockroaches.After Roth (1989a, 2003c).

Characters

Oviparity A

Oviparity B

Ovoviviparity A1

Ovoviviparity B2

Viviparity3

Handling of ootheca

Dropped shortly after

Carried externally

After it is formed,

No ootheca; eggs

After it is formed,

formation

throughout gestation

retracted into the

pass directly into

retracted into

brood sac

brood sac

the brood sac

Physical properties

Hard and dark,

Proximal end is

In most, variably

Incomplete

of egg case

completely enclosing

permeable

reduced and

membrane

eggs

incomplete

Water handling

Sufficient water in

Obtains water from

Obtains water from

Obtains water from

Obtains water

eggs, or additional

the female during

the female during

the female during

from the female

water absorbed from

embryogenesis

embryogenesis

embryogenesis

during embryo-

substrate

genesis

Pre-partition non-

No

Water-soluble

Probably water-

Probably water-

Proteinaceous

yolk nutrients from

material

soluble material

soluble material

secretion from

mother?

walls of brood sac

Taxa

All but Blaberidae

A few Blattellidae

A few Blattellidae,

One tribe of Bla

One known spe

and some Blattel-

most Blaberidae

beridae (Geosca-

cies of Blaberi-

lidae

pheini)

dae

Examples

Periplaneta,

Blattella,

Blaberus,

Macropanesthia,

Diploptera

Eurycotis

Lophoblatta

Nauphoeta

Geoscapheus

punctata

1"False"ovoviviparity of earlier studies. 2"True" ovoviviparity. 3"False"viviparity.

1"False"ovoviviparity of earlier studies. 2"True" ovoviviparity. 3"False"viviparity.

crest, the keel, runs along the mid-dorsal line of the egg case, and at hatch, the nymphs swallow air, forcing open this line of weakness (as in the opening of a handbag). The hatchlings generally exit en masse, and the keel snaps shut behind them (Fig. 7.1). If some eggs are lost due to unviability, parasitism, or disease, the entire brood may fail to hatch, because opening the keel typically requires a group effort. The ootheca is structurally sophisticated (Lawson, 1951; D.E. Mullins and J. Mullins, pers. comm. to CAN), and functions in gas exchange, water balance, and mechanical protection.

The oothecae of oviparous type A cockroaches vary in

Fig. 7.1 Unidentified neonate cockroaches freshly hatched from an ootheca attached to a leaf, Bukit Timah, Malaysia. Note that the keel has snapped shut behind them. Photo courtesy of Edward S. Ross.

their ability to prevent water loss from the eggs (Roth and Willis, 1955c). In some species the ootheca and eggs at oviposition do not contain sufficient moisture for embryogenesis; in these the ootheca must be deposited in a humid or moist environment where the eggs absorb water (e.g., Ectobiuspallidus, Parcoblatta virginica). Alternatively, if the ootheca and eggs contain sufficient moisture for the needs of the embryos at the time of oviposition, the ootheca possesses a protective layer that retards water loss (e.g., Blatta orientalis, Periplaneta americana, Supella longipalpa). The eggs of Blatta orientalis hatch even if oothecae are kept at 0% relative humidity during development. When physically abraded, however, the oothecae lose 60% or more of their water within 10 days,while controls lose only 5% (Roth and Willis, 1955c, 1958a).

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