Most cockroaches that exhibit parental care are subject to risks associated with brood defense and invest time in taking care of offspring. Other costs vary with the form and intensity of parental care. Brooding, for example, is a small investment on the part of the female in relation to potential returns (Eickwort, 1981). In females that carry offspring on their bodies, the burden may hinder locomotion and thus the ability to escape from predators. Energy expended on nest construction can detract from a parent's capacity for subsequent reproduction in those species where parental care occurs in excavated burrows. Insects that utilize nests may also invest time and energy in provisioning and hygienic activities (Tallamy and Wood, 1986). Feeding offspring on bodily secretions may drain stored reserves otherwise devoted to subsequent bouts of oogenesis. The metabolic expenditure may be particularly high in wood-feeding species, whose diet is typically low in nitrogenous materials. The high cost of parental care in Cryptocercus may account for their functional semelparity (Nalepa, 1988b), and has been proposed as a key precondition allowing for the evolution of eusociality in an ancestor they share with termites (Chapter 9). It is of interest then, that, another wood-feeding cockroach (Salganea matsumotoi) that lives in biparental groups and is thought to exhibit extensive parental care appears to have more than one reproductive episode (field data) (Maekawa et al., 2005).
In insects that do not nest in their food source, providing care to young may conflict with feeding opportunities, particularly in species whose diet consists of dispersed or ephemeral items that require foraging over substantial distances. One solution to is to carry one brood while gathering nutrients for subsequent brood development (Tallamy, 1994). To test this hypothesis, it is necessary to determine (1) if females feed while externally carrying nymphs, and (2) if females carrying nymphs are concurrently developing their next set of eggs, incubating eggs in the brood sac, or building reserves for the next brood. We found relevant information on two species. A Pseudophoraspis nebulosa female caught in the field with numerous neonates clinging to the undersurface of her abdomen was dissected, and her brood sac was empty (Shelford, 1906a). In Tho. porcellana, newly hatched nymphs remain in association with their mother for 45 days. After partition another ootheca is formed in 15 to 20 days, and gestation takes 45-52 days. There is therefore a period of time when the female is both internally incubating an ootheca in her brood sac and externally carrying nymphs on her back. However, these are sluggish insects that remain stationary in the leaves on which they feed (Reuben, 1988). At present, then, too little information is available for a fair evaluation of Tallamy's (1994) hypothesis.
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