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

unpubl. obs.). Building activity is most common when
the cockroaches nest in soft, well-rotted logs, and, like
Zootermopsis and some other termites (Wood, 1976;
Noirot and Darlington, 2000), excrement and masticated
wood are the principal construction materials. If logs are
damp, fecal pellets lose their discrete packaging and become
a mass of mud-like frass.
Cryptocercus also exhibits a number of termite-like behaviors
in maintaining a clean house. In addition to expelling
frass from galleries, adults keep the nursery area
(i.e., portion of the gallery with embedded oothecae)
clear of fungal growth and the fecal mud that commonly
lines the walls of galleries in the remainder of the nest
(Nalepa, 1988a). They are known to eat dead nestmates,
but, like termites (Weesner, 1953; Dhanarajan, 1978),
Cryptocercus will bury unpalatable corpses in unused
portions of the gallery (Fig. 9.4B).
DEVELOPMENTAL FOUNDATIONS
The influence of hemimetabolous development in the
evolution of termite societies has long been recognized
(Kennedy, 1947; Noirot and Pasteels, 1987). Unlike the
holometabolous Hymenoptera, termite juveniles do not
have to mature before they are capable of work. Hemimetabolous
insects also tend to grow less between molts
and molt more often over the course of development
(Cole, 1980). This is due, at least in part, to differences in
nutritional efficiency between the two groups. The conversion
of digested food to body mass can be 50% greater
in holometabolous insects, possibly because they do not
need to produce and maintain a large mass of cuticle during
the juvenile stage (Bernays, 1986).
Termite Development
In the Isoptera, day-to-day colony labor is the responsibility
of juveniles—termites whose development has
been truncated, either temporarily or permanently, relative
to reproductives. Even terminal nonsexual stages (i.e.,
soldiers, and workers in some species) are considered immature,
because they retain their prothoracic glands,
which degenerate in all sexual forms. The only imagoes
in the termitary are the king and queen (Noirot, 1985;
Noirot and Pasteels, 1987; Noirot and Bordereau, 1989).
The degree, permanence, timing, and reversal of developmental
arrest, together with the organs subject to these
changes, determine which developmental pathway is
taken during the ontogeny of particular groups (Noirot
and Pasteels, 1987; Roisin, 1990, 2000). This developmental
flexibility is mediated by a combination of progressive,
stationary, and reversionary molts, and is distinctive.
Dedifferentiation of brachypterous nymphs in
termites is the only known instance of a natural reversal
of metamorphosis in insects (Nijhout and Wheeler,
1982). The extraordinary complexity and sophistication
characteristic of termite development is nonetheless
rooted in mechanisms of postembryonic development
observed in non-eusocial insects (Bordereau, 1985). The
developmental characteristics of cockroach ancestors,
then, were the phylogenetic foundation on which termite
polyphenisms were built.
Cockroach Development
Within a cockroach species, both the number and duration
of instars that precede the metamorphic molt are
variable, a trait unusual among hexapods (Heming,
2003). In P. americana, for example, the length of
nymphal period can vary from 134 to 1031 days (Roth,
1981a)—nearly an order of magnitude. The number of
molts in cockroaches varies from 5 or 6 to 12 or 13, and
may or may not vary between the sexes. Within a species,
variation in cockroach development occurs primarily in
response to environmental conditions: low temperature,
minor injuries, water or food deficits, or poor food quality
(Tanaka, 1981; Mullins and Cochran, 1987). Even in
laboratory cultures in which extrinsic influences have
been minimized or controlled, however, the instar of
metamorphosis remains variable, even in nymphs from
the same ootheca (Kunkel, 1979; Woodhead and Paulson,
1983). There can be a lag of up to 9 mon between the appearance
of the first and last adult among nymphs from
the same sibling cohort of Periplaneta australasiae (Pope,
1953), and “runts”—nymphs stalled in the third or
fourth instar when all others in the cohort have matured—have
been noted in P. americana (Wharton et al.,
1968). Kunkel (1979) describes the instar of metamorphosis
in cockroaches as a polygenic trait with a great
deal of environmental input involved in its expression.
Significantly, there are records of both stationary and
saltatory molts in cockroaches (Gier, 1947; Rugg and
Rose, 1990). If the ancestor of the termites was like extant
cockroaches, then it, too, possessed a tremendous
amount of developmental plasticity prior to evolving eusociality.
Control of Development
An examination of conditions known to modify cockroach
development may provide insight into the origins
of termite polyphenism, the proximate causes of which
are still little understood (Bordereau, 1985; Roisin, 2000).
Here we focus on three extrinsic factors that may have
influenced development as the termite lineage evolved:
minor injuries, nourishment, and group effects. Each of
TERMITES AS SOCIAL COCKROACHES 155