Vergara - 1976 - Physiological and morphological adaptability of ri

EXPERIMENTAL APPPMLACH TO INSECT-FLIMKYFE RELNflONSI-IIPS 357
actual temperature and humidity patterns recorded with hygrothennographs in
the field (see also Flitters et al.. 1956).
Early studies with this bioclimatic equipment involved a comprehensive investigation
of the potential favorabilitv of the climates of various agrieulrurally
important areas in the continental United States for the establishment of the fruit
flies D. tiorsafis, D. cucurbftae, and C. capitata (Hitters and Messenger, 1953;
Messenger and Flitters. 1954'. Messenger, 1941). In each climate simulation.
which ran for one full year so that all of the climatic seasons could be examined.
cultures of the different fruit fly species were maintained and all aspects of development.
reproduction. survival, longevity". and population increase and
decrease were observed. For experimental controls. several climates recorded
for places in the Hawaiian Islands were also simulated and fly responses therein
noted and compared with actual population activity‘ in the field.
These studies showed that the species exhibited slightly different tolerances to
heat and cold. The two Dacus species were more tolerant of high temperatures.
while C. cap/ram was more tolerant to cold than the others. 'l'hc overall results
suggested that the species should only find year-long favorable climates in
Florida, southern Texas, and coastal southern Califomia (Messenger and
Flitters. 1.954). All other climatic habitats in the continental United States were
either too cold in tvinter or too hot in summer, or both.
A similar study. conducted with the Mexican fruit fly. A. ludens, led to a somewhat
similar result (Flitters and Messenger. 1965). The Mexican fruit 11y occurs
in Mexico on the east and west coasts almost as far north as the [ntemational
Border. Occasionally the species is trapped in citrus groves in the southem Rio
Grande River valley of south Texas. but the fly is unable to establish there permanently.
The studies led to the conclusion that this species is more tolerant to
both heat and cold than the three Hawaiian species. and that this species should
be able to establish itself successfully in the southeastem and southwestern
United States. including Florida, the coastal zone of the Gulf of Mexico from
Florida west and south to southem Texas, southern California from the International
Border as far north as Riverside. Los Angeles. and Santa Barbara. In
most of these regions. particularly in southem California. while winter cold
would interfere with continuing reproduction (the ovipositional threshold is
12°C). immature stages within the fruit should be able to tivenvinter while
still developing at a very slow rate. The overivintering duration of successful
development could last 5 months.
Since these studies with the various fruit flies. other researchers have acquired
and used similar devices for reproducing climatic patterns. Specht (1972). using
similar equipment tvhich could provide c_vclical temperatures. reproduced the
climatic patterns of apple orchards in Nova Scotia. Canada, in order to observe
the effects of climate on the population dynamics and morphological changes of
the apple aphid, Aphis pomi DeGeer. As already mentioned, Baker (1971, 1972)
used similar equipment to measure the thermal responses of a number of moth
species to British climates to predict potential for invasion.