Vergara - 1976 - Physiological and morphological adaptability of ri

352 CLINIATE AND RICE
Scamens (1923, 1935) ShOWCd that Cooks conclusions relating cutworm outbreaks
and rainfall were not just correlative. but actually based on causal
grounds. Wet spring-summer years raised the level of soil moisture to such a
degree that the normally’ subterranean CUIWOITII larvae were forced to come up
and fied above ground. This resulted in large increases in predation by birds and
mice. as well as increased mortality due to desiccation. which thereby suppressed
the populations to subcconomic levels.
Moisture relations. rather than temperature. have also been shown to be the
limiting factors in the case of the luccrne flea, Sznynrhurirs vrridis (L) in Australia
(1 loldaway‘, 1927), and the Japanese beetle, Popililajaponica Newman.
in the eastern United States (Fox, 1939).
EXPERIMENTAL INSECT BIOCLIMATOLOGY
Because of the marked response of insects to temperature. relative humidity’. and
photoperiod, it is not surprising that early experimental efforts to investigate
climatic relations of important species centered on the use of controlled temperature
and humidity incubators. The first such incubators were only capable of
providing constant conditions of these two climatic factors. Such devices were
fairly easy to construct and use. as they still are at the present time. The first
studies focused on measurement of the effect of constant temperatures on
development (Peairs. 1927'. Uvarov‘, 1931). While many such studies were used
simply to explore the relation of temperature to development as an end in itself,
some few investigators attempted to use their findings to evaluate insect performance
in nature. Such investigations took one of two approaches. In one
approach, the subject insect was exposed to different levels of temperature, relative
humidity. and light. such that pretty‘ much the full range of conditions
within which development could proceed to completion was explored. From
this set of responses the performance of the species in nature where climatic
records were available was then predicted. 1n the other approach. rather than
carry out tests throughout the ranges of the climatic variables, fixed combinations
of the climatic factors in direct correspondence with actual climatic
records were simulated and the responses of the subject insect to these combinalions
were then measured.
One of the early and most ambitious attempts using the first approach referred
to above was that of Bodenheimer (1925. 1938. 1951) who studied the phy-‘siological
life historyj of the Mediterranean fruit fly. Ceratitis capirata (Wiedemann)
at numerous different levels of temperature and relative humidity. He studied
developmental rates, strrvival, and reproductive performance of the fruit fly as
affected by these climatic variables. Then, by means of the equilateral hypcrbola
relation between temperature amd developmental time, he predicted the number
of successive generations that could take place throughout the year at any
selected place. He concluded that those places with climates allowing a large
number of generations per year to take place were more favorable than places
with climates allowing fewer generations per year.