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

Table 3.4. Water balance in Arenivaga. Data are in mg/100 mg/
day at 25°C for a 320 mg nymph. From Edney (1966).
Dry air
88% RH
Water loss
Feces 0.19 0.19
Cuticular and spiracular 5.43 0.65
Total 5.62 0.84
Water gain
Food 0.22 0.44
Metabolism 0.87 0.87
Vapor absorption 0 2.14
Total 1.09 3.45
Fig. 3.11 Morphological structures associated with capturing
atmospheric water in Arenivaga investigata. Top, photograph of
head showing the two dark, spherical bladders protruding
from the mouth. Note hairs around edge of pronotum. From
O’Donnell (1977b), courtesy of M.J. O’Donnell. Bottom, sagittal
view of the head with portions removed to show details of
structures; redrawn from O’Donnell (1981), with permission
of M.J. O’Donnell. The frontal body secretes a fluid that
spreads over everted hypopharyngeal bladders. Atmospheric
water condenses in the fluid and both liquids then flow toward
the esophagus and are swallowed. Arrows indicate route of
fluid movement from site of production in the frontal bodies
to the esophagus.
bladders, one on each side of the mouth (Fig. 3.11). These
are coated with a thick layer of cuticular hairs that hold
and distribute the fluid via capillary action. The fluid is
supplied to the bladders by two glands located on the inside
of the labrum and embedded in a massive muscular
complex that can be seen oscillating when the glands are
secreting fluid. Atmospheric water condenses on the
bladders and is then transferred to the digestive system,
where it is absorbed. The capture of atmospheric moisture
is a solute-independent system, based on the hydrophilic
properties of the cuticular hairs on the bladders
(O’Donnell, 1981, 1982). As a result of this water uptake
system, A. investigata can maintain water balance even if
no free water is available and food contains only 20% water,
provided that air at 82% RH or above is available
(Table 3.4). Females and nymphs are capable of absorbing
water vapor, but males are not (Edney, 1967). Females
are apterous, but males are winged and may be capable of
seeking out free water and higher humidity surface habitats.
The Egyptian species Heterogamisca syriaca is similarly
adapted to desert life. A lipid layer effective up to 56C
protects against evaporation, and the cockroach can extract
water vapor from unsaturated air between 20 and
40C and RH 75% (Vannier and Ghabbour, 1983). Humid
air is available at a depth of 50 cm and at the surface
during the night. Water absorption presumably occurs
via hypopharyngeal bladders, as these have been observed
in H. chopardi (Grandcolas, 1994a). Under the harshest
conditions of water stress, H. syriaca may fast to generate
metabolic water from fat reserves, which are abundant
during the summer months (references in Vannier and
Ghabbour, 1983).
Cockroaches that live in arid zones are rich in potential
for research into behavioral ecology and physiology.
Thorax porcellana living in suspended litter in dry forests
of India, for example, do not actively seek or drink water
56 COCKROACHES