252 SOME ASPECTS OF ECOLOGY 



which quarantine regulations are being drawn up and enforced in 

 progressive states. While probably no quarantine regulations 

 can be devised that will wholly effect the purpose intended, their 

 maintenance has served to check or delay the introduction of 

 many noxious insects, which would have readily entered a country 

 in the absence of such restrictions. 



The strict maritime quarantine upheld at San Francisco, and 

 other Californian ports, appears to be responsible for the effective 

 exclusion of the Mediterranean fruit-fly (Ceratitis capitata) from 

 that state, and the freedom which the whole North American 

 continent has enjoyed from this widespread pest must be largely 

 attributable to similar measures. In Aj^ril, 1929, an infestation 

 of the fruit-fly was discovered in part of Florida. Fortunately 

 the application of effective measures, involving the expenditure 

 of a large sum of money, resulted in its complete eradication. 



The original home of the Mediterranean fruit-fly was probably 

 tropical Africa : from that region it has become very widely 

 spread, probably mainly through fortuitous agencies of commerce. 

 There appears to be no evidence that the insect will become a 

 serious pest in any country where the mean monthly temperature 

 falls to, or below, 10° for three or four consecutive months (Back 

 and Pemberton, 1918). As Verguin (1928) has pointed out, if all 

 the areas known to be infested by this insect be plotted on a 

 world map, they are found to lie almost entirely between the 

 January isotherms of 10° in the two hemispheres. Outside these 

 limits it appears to occur constantly only in territory bordering 

 on the northern Mediterranean coast. It has been reported as 

 causing damage in the environs of Paris, but without becoming 

 regularly established, and in this district it is stated to be capable 

 of passing through only two generations per year as compared 

 with four on the Mediterranean littoral. The available informa- 

 tion respecting this insect all points to temperature being the most 

 important of the climatic factors concerned : the optimum 

 conditions are a warm and more or less equable climate which, at 

 the same time, allows of a continuous supply of some or other of 

 the host-fruits being available throughout the year. In Europe 

 the insect is largely checked by winter temperatures which 



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