Vergara - 1976 - Physiological and morphological adaptability of ri

358 CLIMAJE AND RICE
BIOCLINLNPIC
INDEX
1t has been seen from the review thus far that insects respond differently to such
factors as temperature and relative humidity according to what vital process is
under observation. Development. reproduction, survival. and adult longevity
are the processes that have most frequently been measured. l-lourever. at a
quantitative level. these responses are not all the same. Hence for the spotted
alfalfa aphid. T. tnfofii, the optimum temperature for development is different
from that for reproduction. and both are different in relation to longevity’ and
survival. The tolerance ranges for these different processes are also different.
with development usually showing the widest tolerance to temperature, and
reproduction the IIQITOHItISI.
What is wanted is some single index that could reflect all or many of these
different responses at one and the same time. Then a single index of climatic
favorability or unfavorability’ could be used. Such an index has been proposed in
the form of the intrinsic rate of numerical increase r.._ (Messenger, 1964b). This
parameter. the growth constant in the equations for exponential and logistic
population grovt-‘th. is a weighted measure of rate of development. rate of reproduction,
and rate of survival (Andrewartha and Birch, 1954). Any extrinsic
factor of the environment that affects any of these three rates will also affect r...
The effects of fluctuating and constant temperatures and humidities on T.
trgfblii‘ have been determined (Messenger. 1964a). The optimal temperature for
n. is 295°C. the lower thermal limit is 8°C. and the upper thermal limit is 322°C.
Climatic factors affect the growth constant in a graded way. and therefore there
is a temperature-tolerance relationship for this parameter just as there is for the
different vital processes of development, reproduction, and survival taken separately.
One could then say that for any given climate, an index of favorabilitv
could be the intrinsic grotirth rate parameter.
constant. the more favorable are the environmental circumstances, climate for
example. within which the population resides.
Other investigators of the effects of climatic factors on insect ecology have
also used this index. Siddiqui and Barlow (1972, 1973a, 1973b) in bioclimatie
studies of the pea aphid, the vinegar fly“. and the Mediterranean flour moth. use
the intrinsic grotvth rate as an indicator of response to temperature. for example.
As will he described in detail in the following section. this parameter has also
been used to evaluate parasitoid performance and potential effectiveness in
relation to climate (Messenger. 1964a‘. Force and Messenger, 1964b; Messenger,
1970).
BIOCLIMATTC STUDIES WITH INSECT PARASITUIIJS
It is only natural that bioclimatic techniques of study which have customarily
been applied to phy-‘tophagotts insect species should also be used in investigations
of the physical eeologies of insect parasitoids. lndeed. many introductions of