Vergara - 1976 - Physiological and morphological adaptability of ri

348 crLnuATs AND RICE
Experimental studies on insect bioclimatics. on the other hand. are those in
which the insect in question is exposed to controlled climatic variables in the
laboratory or in the field, and conclusions about the insects bioclimatic characteristics
are drawn directly from the results of the experiments. Constant teinpcrature
incubators. environmental control chambers or bioclimatic chambers
are the principal pieces of equipment used for such bioclimatic studies. These
are the entomological equivalents of phytotrons. or plant growth chambers.
Climates are composed of a large number of factors involving aspects of atmospheric
heating and cooling (insolation, radiation); sunlight intensity". air
movement (wind); moisture content of the air (relative or absolute humidity.
saturation deficit); moisture condensation from the air (rain. snow. hail, ice.
dew); cloud and overcast; barometric pressure; percentage of sunshine. and
so on. In certain zones of the earth (temperate. subarctic, arctic). the length of
the growing season (frost-free days) is a measurable aspect of the seasonality of
climate, as are allemations of wet and dry seasons in arid, semiarid, or monsoon
regions.
Not all of these individualized factors are important to any particular form of
life or occur at dominant intensities at a particular place. Those factors considered
important in insect ecology are temperature, relative humidity, evapora~
tion. precipitation in certain respects, wind. and photoperiod. Because of its
very strong interaction with the insects physiological systems. temperature is
probably the most important and widely studied climatic factor in insect bioclimatology.
Because insects. particularly terrestrial species. always have a
problem of water balance. water retention, and evaporative water loss, relative
humidity ranks close to temperature as an important limiting factor for insects.
Photoperiod is a third, very influential factor. particularly for temperate or
subarctic or arctic species, particularly those that must withstand winter cold or
summer dryness. Thus. most experimental studies of insects and climate involve
one or more of these three major factors.
The features of insect life that respond to or are most sensitive to climatic
factors are numerous and complex. Biological systems that are influenced by
climate are physiological, behavioral. and populational. With respect to temperature.
practically every conceivable life process is affected, including development,
hatching, melting, pupation. ecdysis, diapause, spennatogenesis, and ovigenesis.
Behavioral processes affected include crawling. feeding, webbing.
cocoon spinning, flight. courtship. mating, oviposition. and nest building. At the
populational level, such aspects as birth rates. death rates, rates of increase in
numbers. dispersal. and migration are all affected by climate. Any one of these
features, physiological. behavioral. or populational. may be the single most
important feature influenced by climate.
For any one climatic factor. different factor intensities induce different
amounts of response. At extremes of factor value, the typical response may be
inhibited. This relationship has been called "Shelfords law of tolerance"
(Odum. 1971). Using temperature. for example, there is a tolerance range of