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

Fig. 4.2 Feeding and drinking cycles in relation to the reproductive
cycle of the wood cockroach Parcoblatta fulvescens.
Filled circles, water consumption; open squares, food consumption;
EC, egg case formation; ECD, egg case deposition.
From Cochran (1986b), courtesy of Donald G. Cochran, with
permission from Elsevier Press.
but no water, they lived for about the same period of time
as those deprived of both. If they are provided with water,
most lived longer. Some species can live for 2 to 3 mon
on water alone, and others significantly longer. Virgin females
of Eublaberus posticus live an average of 360 days on
water alone, whereas starved but mated females can live
an average of 8 mon and are even able to produce 1 or 2
litters, yielding about 26 young. One female mated at
emergence was starved for 252 days, during which time
she produced 2 litters totaling 50 nymphs. She was then
given food on day 252 (and thereafter), mated again 4
days later, and lived an additional 525 days, producing 5
more oothecae from which 24, 18, 5, 1, and 0 nymphs
hatched. Although this female had been starved for the
first 8 mon of adult life, after food was made available she
managed to give birth to a total of 98 offspring, which is
about normal for this species (Roth, 1968c).
There is a significant difference in starvation resistance
between males and females in cockroach species exhibiting
sexual dimorphism in body size. In Table 4.3, males
and females are of similar size only in Neostylopyga rhombifolia,
Eurycotis floridana, and Nauphoeta cinerea; in
these cases, survival of males and females is similar. In the
remaining species males are significantly smaller than females
and are more vulnerable to starvation. A larger
body size is correlated with bigger fat bodies and their accumulations
of carbohydrates, lipids, and uric acid; these
reserves can be rapidly mobilized on demand (Mullins
and Cochran, 1975b; Downer, 1982). The nutrients and
water housed in developing oocytes are additional resources
available to starving females. The strategy for a
food-deprived female of P. americana seems to involve resorption
of yolk-filled eggs, storage of their yolk proteins,
and then rapid incorporation of protein into eggs when
feeding re-ensues (Roth and Stay, 1962b; Bell, 1971; Bell
and Bohm, 1975).
A variety of digestive attributes help cockroaches
buffer food shortages. The large crop allows an individual
to consume a substantial quantity of food at one time.
This bolus then acts as a reservoir during periods of fasting.
When fully distended with food, the crop is a pearshaped
organ about 1.5 cm in length and 0.5 cm at its
widest part (in Periplaneta australasiae). It extends back
to the fourth or fifth abdominal segment, crowding the
other organs and distending the intersegmental membranes.
A meal may be retained in the crop for several
days (Abbott, 1926; Cornwell, 1968). Solid food is also retained
in the hindgut of starving P. americana for as long
as 100 hr, although the normal transit time is about 20 hr
(Bignell, 1981); this delay likely allows microbial biota to
more thoroughly degrade some of the substrates present,
particularly fiber. The functional significance of intestinal
symbionts increases in times of food deficiency and helps
to maintain a broad nutritional versatility (Zurek, 1997).
A starving cockroach is thus indebted to its microbial
partners on two counts: first, for eking out all possible nutrients
in the hindgut, and second, for mobilizing uric
acid stored in the fat body (Chapter 5). When food is
again made available, starved P. americana binge. After
starving for 13 days the amount of food consumed rose
to five times the normal level, then leveled off after approximately
20 days. Greater consumption was accomplished
by larger and longer meals, not by increasing the
number of foraging trips (Rollo, 1984a).
PLANT-BASED FOOD
There is little evidence that any cockroach species is able
to subsist solely on the mature green leaves of vascular
plants. There are reports of occasional herbivory, such as
that of Crowell (1946), who noted that the small, round
leaves of the aquatic plant Jussiaca are included in the diet
of Epilampra maya. Often, cockroaches that appear to be
feeding on green leaves are actually eating either a small,
dead portion at the leaf edge or around a hole, or other
material on the leaf (WJB, unpubl. obs.). To test the extent
to which tropical cockroaches include fresh vegetation
in their diets, WJB set up a series of two-choice tests
in laboratory cages at La Selva Biological Station in Costa
Rica. Ten species of cockroaches were tested: Capucina
sp., Cariblatta imitans, Epilampra involucris, Ep. rothi, Ep.
unistilata, Latiblattella sp., Imblattella impar, Nahublattella
sp., Nesomylacris sp., and X. hamata. The insects were
offered a choice of green leaves versus dead leaves of the
same plant species; only leaves eaten readily by local Or-
66 COCKROACHES