The simplest form of parental care in cockroaches is brooding, defined as a short-term association of mother and neonates. In a number of ovoviviparous blaberids (e.g., N. cinerea, Blab. craniifer), young nymphs cluster under, around and sometimes on the female for varying periods of time after emergence. Most brooding associations last less than a day. Although observations of brooding behavior are based primarily on laboratory observations, Grandcolas (1993a) observed it in Than. akinetum in the field. The female was perched on a leaf when first instars emerged, and the nymphs aggregated beneath the mother's body for several hours prior to dispersing. In cockroaches known to brood, aggregation of the nymphs also occurs in the absence of the female; it is not solely predicated on all nymphs orienting to their mother as a common stimulus (Evans and Breed, 1984).
It is generally believed that brooding has a protective function; it takes several hours for the cuticle of neonates to harden, and soft, unpigmented nymphs are at risk from ants and cannibalism (Eickwort, 1981). The transfer of gut microbiota may also be a factor; short-term contact with the female may be necessary so that neonates secure at least one fecal meal (Nalepa and Bell, 1997). There are, however, no published observations or studies relating to the functional significance of brooding.
We place cockroaches that exhibit brooding behavior into a category separate from other subsocial species because short-term maternal presence alone defines the behavior. Although the female may stilt high on her legs to accommodate the nymphs beneath her (e.g., Homalop-teryx laminata—Preston-Mafham and Preston-Mafham, 1993; Nauphoeta cinerea—Willis et al., 1958), there are currently no reports of active maternal feeding or defense in species placed in this group. More detailed study may indicate that at least some of these species are subsocial. We classified G. portentosa as exhibiting brooding behavior (Nalepa and Bell, 1997), when in fact it exhibits short-term, but elaborate parental care. After partition the female expels a sizable gelatinous mass that is eaten eagerly by neonates (Fig 8.3A) (Perry and Nalepa, 2003). Young nymphs then collect under the mother, who is aggressive to intruders and hisses at the slightest disturbance (Roth and Willis, 1960).
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