COMBINATIONS OF ENVIRONMENTAL FACTORS 



209 



ten this lies near the maximum temperature 

 limit and above 50 per cent relative hu- 

 midity. Optimum conditions for human 

 health are placed by Huntington (1919) at 

 a mean temperature of 64° F. and a relative 

 humidity of 80 per cent. 



The closeness with which temperature- 

 humidity means or extremes of a given 

 habitat approximate the optimum require- 

 ments and tolerations of a species is an 



other factors being equal, in a year like 

 1927 than in one like 1932. Ecological re- 

 quirements being known, prospective popu- 

 lation levels can be predicted vdth some 

 accuracy. 



The other locaUties whose temperature- 

 humidity graphs are shown in Figure 50 

 were selected to test the favorabihty of their 

 cUmatic condition for the development of 

 the Mediterranean fruit fly. Paris presents 



RELATIVE HUMIDITY IN PER CENT 



Fig. 49. Percentage of mortality of eggs of the desert locust at difFerent combinations of tem- 

 perature and humidity. ( Rearranged from Bodenheimer. ) 



important factor helping to determine popu- 

 lation density both for a given year and for 

 many years together. The Mediterranean 

 fruit fly {Cer otitis capitata) thrives best in 

 temperatures that range from 16° to 32° C. 

 and in relative humidities between 65 and 

 75 per cent. The combined range of opti- 

 mum temperature-humidity relations are 

 indicated in Figure 50 by the smallest 

 quadrangle. Conditions are favorable for the 

 development of this fruit fly in the wider 

 range shown by the middle quadrangle, and 

 the Hmits of toleration are outlined by the 

 largest one. In Tel Aviv, Palestine, these 

 climatic factors are favorable the year 

 around and may be optimal during the 

 major part of the year. As is usual in many 

 parts of the world, there is a considerable 

 variation from one year to another, and a 

 much larger population could be expected, 



relatively adverse conditions during the 

 cooler six months of the year without trans- 

 gressing the Umits of toleration. Ankara has 

 an intolerable climate for three months, and 

 Kartoum for nine months each year. Hawaii 

 is favorable, as is Tampa, Florida, (not 

 shown on the chart). Some danger of im- 

 portant outbreaks could be expected if the 

 fly gained a foothold at Los Angeles, Cali- 

 fornia, where there are nine favorable 

 months. Large populations could not be ex- 

 pected in CaUfomia's dry interior, irrigated 

 regions aside, because of a sequence of four 

 months of extremely low humidity. 



This introduces the concept of bonitation 

 (Bodenheimer, 1938). Bonitation may be 

 regarded as the state of well-being of a 

 species or community as shown by its popu- 

 lation density. Estimates of climatic control 

 of bonitation were originally based primarib' 



