364
E. B. EDNEY
ment, perhaps, is the remarkable ability of desert species to undergo long
periods of starvation. Dinothrombid mites feed only once a year, scorpions
can exist for months without food, and the beetle, Blaps requieni, lived
for 5 years without food according to Cloudsley-Thompson and Chadwick
(1964). In addition, many species enter diapause during difficult periods:
the red locust, Nomadacris, for example, diapauses as an adult in the dry
season. The desert locust, Schistocerca, is delayed in reaching sexual maturity if it feeds on senescent vegetation (Ellis and Carlisle, 1965), a striking adaptation which has the effect of coordinating oviposition and the
appearance of young hoppers with the onset of rains and the growth of
green vegetation.
A. PHENOLOGY OF LOCUSTS
Locust eggs require water to develop, nymphs require plentiful green
vegetation to feed on, and adults need fresh food to develop sexual maturity and moist ground in which to lay eggs (Woodrow, 1965a,b). Yet
these insects live in deserts. This underlines several important points about
the relationship of arthropods and deserts : ( 1 ) that deserts are not always
dry, (2) that in areas which are by and large very dry, humid niches exist,
(3) that physiological mechanisms which combine to time the occurrence of
the various stages of development are important, and (4) that behavioral
mechanisms (including the formation of swarms) may permit survival in
an otherwise impossible environment.
The story of locust migrations has been well told by Rainey and others
(Rainey, 1951; Rainey et al., 1957). The direction in which flying swarms
move is determined by the prevailing wind, and since these winds usually
blow into areas of convergence of air masses where rain falls, locust
swarms by and large are also conveyed to places where conditions are
admirably suited for egg laying and hopper development.
The changes in behavior, physiology, and morphology which occur as
locusts pass from the "solitary" phase, where they are no more than grasshoppers, to the "gregarious" phase, when they swarm and inflict so much
damage, are fascinating examples of adaptations to desert conditions. The
buildup, from September through November, 1967 of an outbreak of the
desert locust in the Tamesna area of Mali and Niger Republics has been
vividly described by Roffey and Popov (1968). These authors recognize
three stages in the process—concentration, multiplication, and gregarization—and they stress that by observing different groups of insects in
different localities, examples of all three stages in the process could be
found at any one time, although concentratioon was more frequent early
on and gregarization later.
E. B. EDNEY
ment, perhaps, is the remarkable ability of desert species to undergo long
periods of starvation. Dinothrombid mites feed only once a year, scorpions
can exist for months without food, and the beetle, Blaps requieni, lived
for 5 years without food according to Cloudsley-Thompson and Chadwick
(1964). In addition, many species enter diapause during difficult periods:
the red locust, Nomadacris, for example, diapauses as an adult in the dry
season. The desert locust, Schistocerca, is delayed in reaching sexual maturity if it feeds on senescent vegetation (Ellis and Carlisle, 1965), a striking adaptation which has the effect of coordinating oviposition and the
appearance of young hoppers with the onset of rains and the growth of
green vegetation.
A. PHENOLOGY OF LOCUSTS
Locust eggs require water to develop, nymphs require plentiful green
vegetation to feed on, and adults need fresh food to develop sexual maturity and moist ground in which to lay eggs (Woodrow, 1965a,b). Yet
these insects live in deserts. This underlines several important points about
the relationship of arthropods and deserts : ( 1 ) that deserts are not always
dry, (2) that in areas which are by and large very dry, humid niches exist,
(3) that physiological mechanisms which combine to time the occurrence of
the various stages of development are important, and (4) that behavioral
mechanisms (including the formation of swarms) may permit survival in
an otherwise impossible environment.
The story of locust migrations has been well told by Rainey and others
(Rainey, 1951; Rainey et al., 1957). The direction in which flying swarms
move is determined by the prevailing wind, and since these winds usually
blow into areas of convergence of air masses where rain falls, locust
swarms by and large are also conveyed to places where conditions are
admirably suited for egg laying and hopper development.
The changes in behavior, physiology, and morphology which occur as
locusts pass from the "solitary" phase, where they are no more than grasshoppers, to the "gregarious" phase, when they swarm and inflict so much
damage, are fascinating examples of adaptations to desert conditions. The
buildup, from September through November, 1967 of an outbreak of the
desert locust in the Tamesna area of Mali and Niger Republics has been
vividly described by Roffey and Popov (1968). These authors recognize
three stages in the process—concentration, multiplication, and gregarization—and they stress that by observing different groups of insects in
different localities, examples of all three stages in the process could be
found at any one time, although concentratioon was more frequent early
on and gregarization later.