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

Barth, 1985). In some blattellids the internal glandular
apparatus is enormous. Blattella meridionalis has glands
that form elongate sacs extending well into the next abdominal
segment (Roth, 1985). In the panteli group of
Phyllodromica the internal reservoirs consist of two pairs
of long tubular pouches (Fig. 6.8). The anterior pair is
thick, branched in some species, and open to the exterior
via an open bowl or pocket. The posterior pair of tubules
is very thin and unbranched, with small openings that lie
behind the larger openings of the anterior glands (Bohn,
1993).
Functional Significance
External pits, “bowls,” or depressions function as reservoirs
for the tergal secretion oozing up from underlying
glandular cells (Roth, 1969; Brossut and Roth, 1977;
Sreng, 1979b). In some instances, drops of liquid can be
seen forming at the opening of the gland as the female
feeds (e.g., R. maderae—Roth and Barth, 1967). The secretion
produced by the tergal glands is a mixture of
short-range volatile and non-volatile fractions, the latter
including protein, lipids, and carbohydrates (Brossut et
al., 1975; Korchi et al., 1999). The best-studied, that of B.
germanica, is a complex synergistic mixture of polysaccharides,
17 amino acids, and lipids, including lecithin
and cholesterol. Maltose, known from baiting studies to
be a potent phagostimulant for the species, is one of the
primary sugars (Kugimiya et al., 2003; Nojima et al.,
1999a, 1999b). There is little relationship between response
to the secretion and sexual receptivity. Both sexes
and all stages are attracted (Nojima et al., 1999b). Because
tergal secretions exploit a female’s underlying motivation
to feed, they can be classified as “sensory traps” (Eberhard,
1996). They mimic stimuli that females have
evolved, under natural selection, for use in other contexts.
It is uncertain to what degree tergal secretions provide
a nutritional boost to grazing females. The behavior is
most often described as “licking” or “palpating,” but the
action of the female’s mandibles and the manner in which
she presses her mouthparts against the male’s gland indicate
that she actually eats the secretion. The male typically
lets her feed 3–7 sec before attempting to make genitalic
connection (Roth and Willis, 1952a; Barth, 1964; Roth,
1969). Females of Eurycotis floridana may graze for nearly
a minute, longer than any other studied species (Barth,
1968b). Feeding may also be “quite prolonged” in Periplaneta
spp., with the female vigorously biting the tergite.
The male gland in Rhyparobia maderae can be extensively
scarred (Simon and Barth, 1977b), attesting to female enthusiasm
for the fare. Roth (1967c) suggested that in
species with very deep, well-developed tergal glands located
near the base of the male’s wings, females may feed
on tergal secretions during the entire period of copulation,
that is, they may not rotate off the male’s back into
the opposed position. The extent to which tergal glands
provide females with a significant source of nourishment
is in need of examination, particularly in species with
large glandular reservoirs. In many insects with courtship
feeding the food gift provides no significant nutritional
benefit to the female (Vahed, 1998). The amount of secretion
ingested by B. germanica does seem negligible. On
the other hand a female may feed on the tergal secretion
of the male 20 times in a half hour without resultant copulation
(Table 6.2), and courtship activities can deplete
the gland (Kugimiya et al., 2003).
Blattella germanica is a good example of the concept
that in species utilizing sensory traps, males are selected
to exaggerate the attractiveness of the signal while minimizing
its cost (Christy, 1995). The German cockroach
has double pouches on the seventh and eighth tergites,
with the ducts of underlying secretory cells leading to the
lumen of the pouch (Roth, 1969). During courtship, the
female feeds on the secretions in the cavities on the eighth
tergite. After 2–5 sec, the male slightly extends his abdomen,
causing the female to switch her feeding activities
to the gland on the seventh tergite, triggering genitalic extension
on the part of the male. The female can contact
the tergal secretions with her palps, but the cuticular
openings of the glands are too small to permit entry of the
mandibles and allow a good bite. She plugs her paraglossae
into the cavities and ingests the tiny amount of glandular
material that sticks to them. The forced lingering as
she repeatedly tries to access the secretions keeps her positioned
long enough for a copulatory attempt on the part
of the male (Nojima et al., 1999b). The tergal glands in B.
germanica are akin to cookie jars that allow for the insertion
of your fingers but not the entire hand. The design
encourages continued female presence, but frugally dispenses
what is presumably a costly male investment.
Males of other species may take a more direct approach
to “encouraging” females to maintain their position. In a
number of Ischnoptera spp., the tergal gland is flanked by
a pair of large, heavily sclerotized claws, each of which has
four stout, articulated setae forming the “fingers.” When
the female is feeding on the tergal gland she must place
her head between these claws “and probably applies pressure
to the articulated setae” (Roth, 1969, Figs. 47–53;
Brossut and Roth, 1977, Figs. 18–19). These structures,
however, are quite formidable for simple mechanoreceptors,
and may function in restraining the female rather
than for just signaling her presence.
Because tergal secretions are sampled by the female
prior to accepting a male or his sperm, they may provide
a basis for evaluating his genetic quality, physiological
condition (Kugimiya et al., 2003), or in some species, his
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