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

The most sophisticated pattern of nitrogen excretion
occurs in at least nine species in the Blattellinae (Parcoblatta,
Symploce, Paratemnopteryx), which void discrete,
formed pellets high in urate content. These pellets
are distinct from fecal waste (Fig. 5.8), suggesting that the
packaging does not occur by chance. The cockroaches
store urates internally as well (Cochran, 1979a). The level
of dietary nitrogen in relation to metabolic demand for
nitrogen is the controlling factor in whether uric acid is
voided (Cochran, 1981; Cochran and Mullins, 1982;
Lembke and Cochran, 1990). This is nicely illustrated in
Fig. 5.9, which shows urate pellet excretion in female Parcoblatta
fulvescens on different diets over the course of a
reproductive cycle. Excreted urate pellets serve as a type
of external nitrogen storage system, which may be accessed
either by the excretor or by other members of the
social group in these gregarious species. Reproducing females
have been observed consuming the urate pellets,
and they do so primarily when they are on a low-nitrogen,
high-carbohydrate diet. A female carrying an egg
case was even observed eating one, although they do not
normally feed at this time. This system allows the cockroaches
to deal very efficiently with foods that vary widely
in nitrogen content. High nitrogen levels? The cockroaches
store urates up to a certain level, and beyond that
they excrete it in the form of pellets. Nitrogen limited?
They mobilize and use their urate fat body reserves. Nitrogen
depleted? They scavenge for high-nitrogen foods,
including bird droppings and the urate pellets of conspecifics.
Nitrogen unavailable? They slow or stop reproduction
or development until it can be found (Cochran,
1986b; Lembke and Cochran, 1990).
Implications of the Bacteroid-Urate System
The bacteroid-assisted ability of cockroaches to store,
mobilize, and in some cases, transfer urates uniquely allows
them to utilize nitrogen that is typically lost via excretion
in the vast majority of insects (Cochran, 1985).
These symbionts thus have a great deal of power in structuring
the nutritional ecology and life history strategies
of their hosts. Bacteroids damp out natural fluctuations
in food availability, allowing cockroaches a degree of independence
from the current food supply. An individual
can engorge prodigiously at a single nitrogenous bonanza,
like a bird dropping or a dead conspecific, then
later, when these materials are required for reproduction,
development, or maintenance, slowly mobilize the stored
reserves from the fat body like a time-release vitamin. The
legendary ability of cockroaches to withstand periods of
starvation is at least in part based on this storage-mobilization
physiology. The beauty of the system, however, is
that stored urates are not only recycled internally by an
individual, but, depending on the species, may be transferred
to conspecifics, and used as currency in mating and
parental investment strategies. Any individual in an ag-
Fig. 5.8 “Salt and pepper” feces of Paratemnopteryx ( Shawella) couloniana; male, right; female
and ootheca, left. The pile of feces to the left of the ootheca shows the variation in color of the
pellets. Some of these have been separated into piles of the dark-colored fecal waste pellets (above
the female) and the white, urate-filled pellets (arrow). Photo courtesy of Donald G. Cochran.
MICROBES: THE UNSEEN INFLUENCE 85