VI. DESERT ARTHROPODS
331
In many vertebrates the water content and volume of urine is under
endocrine control, particularly by the antidiuretic hormone from the neurohypophysis of the pituitary gland. In insects too there is growing evidence
of hormonal control of urine production. One of the earliest demonstrations was that of Nunez (1956) who found neuro-endocrinal control in
Anisotarsus; but recently, particularly following the work of Maddrell
(1962) and Berridge (1965, 1966), the field has been very active and,
as an almost inevitable consequence, conclusions have been tentative and
sometimes conflicting. Good reviews by Maddrell (1967, 1970, 1971) exist, and I shall do no more than draw attention to certain aspects of the
work which are of interest in the present context.
It seems that both diuretic and antidiuretic factors exist. The former
are more commonly observed, but the latter have been demonstrated in
Periplaneta (Wall and Ralph, 1964; Wall, 1967; de Bessé and Cazal,
1968; Mills, 1967), in Locusta and Gryllus (de Bessé and Cazal, 1968),
and perhaps in others. The sites of production and release of the factors
are various: the protocerebrum and corpora cardiaca of the stick insect,
Carausius (Pilcher, 1970a,b), the corpora allata in Periplaneta (Mills,
1967; Wall and Ralph, 1964), the mesothoracic ganglia of Rhodnius
(Maddrell, 1964), and the terminal abdominal ganglion of Periplaneta
(Mills and Whitehead, 1970).
Pilcher (1970a) points to a number of interesting adaptive differences
between the systems in Rhodnius and Carausius. The former feeds infrequently on blood, while the stick insect feeds continually on green plant
material. In Rhodnius, diuretic hormone is released only after a meal, and
the Malpighian tubules respond fully even to a low concentration, while
in Carausius, hormone is produced continuously in small quantities, and
the tubules respond only to rather high concentrations. Rapid onset of
diuresis is ensured in Rhodnius by release of the hormone close to the
site of action by peripheral abdominal nerves (Maddrell, 1966), but in
Carausius, where disturbance of water balance is less sudden or large, the
hormone is released anteriorly, perhaps by the corpora cardiaca, and is
conveyed to the tubules by hemolymph.
Mordue (1969) has used the desert locust (Schistocerca gregaria)
to demonstrate the interesting fact that, in this insect at least, a diuretic
factor from the corpora cardiaca exerts its effect in two different ways on
two separate target organs: urine production by the tubules is increased,
while résorption from the rectum is inhibited.
Exploration of this fast growing and fascinating field of hormonal control of water balance in arthropods is only just beginning. The processes
are of the greatest significance in the lives of desert forms, and there can
331
In many vertebrates the water content and volume of urine is under
endocrine control, particularly by the antidiuretic hormone from the neurohypophysis of the pituitary gland. In insects too there is growing evidence
of hormonal control of urine production. One of the earliest demonstrations was that of Nunez (1956) who found neuro-endocrinal control in
Anisotarsus; but recently, particularly following the work of Maddrell
(1962) and Berridge (1965, 1966), the field has been very active and,
as an almost inevitable consequence, conclusions have been tentative and
sometimes conflicting. Good reviews by Maddrell (1967, 1970, 1971) exist, and I shall do no more than draw attention to certain aspects of the
work which are of interest in the present context.
It seems that both diuretic and antidiuretic factors exist. The former
are more commonly observed, but the latter have been demonstrated in
Periplaneta (Wall and Ralph, 1964; Wall, 1967; de Bessé and Cazal,
1968; Mills, 1967), in Locusta and Gryllus (de Bessé and Cazal, 1968),
and perhaps in others. The sites of production and release of the factors
are various: the protocerebrum and corpora cardiaca of the stick insect,
Carausius (Pilcher, 1970a,b), the corpora allata in Periplaneta (Mills,
1967; Wall and Ralph, 1964), the mesothoracic ganglia of Rhodnius
(Maddrell, 1964), and the terminal abdominal ganglion of Periplaneta
(Mills and Whitehead, 1970).
Pilcher (1970a) points to a number of interesting adaptive differences
between the systems in Rhodnius and Carausius. The former feeds infrequently on blood, while the stick insect feeds continually on green plant
material. In Rhodnius, diuretic hormone is released only after a meal, and
the Malpighian tubules respond fully even to a low concentration, while
in Carausius, hormone is produced continuously in small quantities, and
the tubules respond only to rather high concentrations. Rapid onset of
diuresis is ensured in Rhodnius by release of the hormone close to the
site of action by peripheral abdominal nerves (Maddrell, 1966), but in
Carausius, where disturbance of water balance is less sudden or large, the
hormone is released anteriorly, perhaps by the corpora cardiaca, and is
conveyed to the tubules by hemolymph.
Mordue (1969) has used the desert locust (Schistocerca gregaria)
to demonstrate the interesting fact that, in this insect at least, a diuretic
factor from the corpora cardiaca exerts its effect in two different ways on
two separate target organs: urine production by the tubules is increased,
while résorption from the rectum is inhibited.
Exploration of this fast growing and fascinating field of hormonal control of water balance in arthropods is only just beginning. The processes
are of the greatest significance in the lives of desert forms, and there can