Jan. 15. 1915 Citrous Fruits and Mediterranean Fruit Fly 327 



The general effect of retarded development of the fruit fly due to cold 

 weather is to increase the mortality among all stages. Even pupse are 

 subject to an increasing rate of mortality the longer they are subjected 

 to lower temperatures. Adults seem more able to withstand prolonged 

 cold weather than any of the other stages. One individual was kept 

 alive bv daily feeding for 4K months during a Hawaiian winter and 

 spring. However, during the cooler months the adults are more sluggish 

 and fall more easily a prey to adverse climatic conditions, such as heavy 

 winds and rains, and to predaceous insects. Mr. George Compere reports 

 having seen adults sunning themselves on orange trees in Spain after a 

 night during which the temperature dropped to freezing, thus showing 

 that adults can withstand temporarily any cold snap likely to occur in a 

 citrous section. However, the fact that adults do not succeed in thriving 

 during the winter temperatures of southern Spain and Italy and in 

 Sicily seems to be well proved by the fact that it is only during the 

 summer and early fall that the fruit fly becomes a serious pest in favored 

 host fruits and in overripe citrous fruits. If this were not so, fruits 

 would become badly infested much earlier in the season than they do. 

 The number of adults surviving the winter must be very small. Even 

 the mild winters of Hawaii at Honolulu have a very noticeable effect 

 upon the numerical abundance of the adult flies, as shown by trap experi- 

 ments extending over one full year. 



In addition to this beneficial effect of lower winter temperatures, both 

 California and Florida growers will receive further protection as a result 

 of the conditions surrounding the growing of Citrus as a commercial 

 proposition. In the Hawaiian Islands, especially about Honolulu, citrous 

 fruits are subjected to the most severe attack imaginable under field 

 conditions. They are attacked over long periods by an abundance of 

 fruit flies that mature in many host fruits ripening at intervals through- 

 out the year on all sides of isolated citrous trees. The number of wild 

 fruits in which the fruit fly can breed in the citrous regions of California 

 and Florida is, in comparison with Hawaii, so extremely small that the fly 

 would find conditions unfavorable for rapid increase, even if weather condi- 

 tions were more favorable. In many instances large acreages of Citrus oc- 

 cur where vegetation is normally decidedly stunted unless irrigation is prac- 

 ticed. With the excellent work of the horticultural inspectors in California 

 a reduction of the noncitrous host fruits in and about citrous groves is a 

 practical proposition. Even near-by orchards of drupe fruits are not 

 the menace that they seem to many, inasmuch as their crops are unsuit- 

 able for fly attack except during short periods of the year. The very 

 scarcity of vegetation that can not be destroyed which produces fruits 

 subject to fruit-fly attack makes it possible to attach a far greater impor- 

 tance in California and Florida than in the Hawaiian Islands to the 

 excessive mortality of the fly discussed in this paper. It has been shown 



