Jan. .5. 191S Citrous Fruits and Mediterranean Fruit Fly 329 



CONCLUSION 



Citrous fruits are not the favored host fruits of the Mediterranean 

 fruit fly (Ceratiits capitata Wied.) that the earlier writers thought. 

 While grapefruit, oranges, lemons, and many limes may become quite 

 badly infested with well-grown larvae if allowed to remain on the tree 

 long after they become sufficiently ripe for the market, nature has so 

 well equipped them to withstand attack that larva; are seldom found in 

 their pulp imtil they are much overripe. Oranges and grapefruit are 

 generally eaten and found uninfested if gathered as they ripen. Indeed, 

 in Honolulu, where conditions are very favorable to early infestation of 

 the pulp, owing to the excessive numbers of adult flies breeding in a 

 large number of host fruits ripening in rapid succession, it is doubtful 

 whether grapefruit, oranges, and lemons would ever become infested 

 until long after becoming overripe if the female fly formed a fresh egg 

 cavity for each batch of eggs deposited, for the reason that the eggs and 

 the young larvse found in the egg cavity and in the rag of the rind would 

 then be forced always to face well-nigh insurmountable difliculties. 

 The oil of the cells ruptured in the formation of the egg cavities kills a 

 large percentage of the eggs and newly-hatched larvae. Larvae that 

 succeed in entering the rag from the egg ca\ity are able to reach the 

 pulp in astonishingly small numbers because of the imperviousness of 

 the rag. It is only the persistent attack of successive lots of larvas 

 hatching from different batches of eggs laid in the same puncture in 

 which the oil has become inoperative that finally breaks down the barrier 

 between the young lar\'ae and the pulp. 



The Mediterranean fruit fly is quickly affected by low temperatures. 

 A temperature of about 56° F. has lengthened the time required by the 

 fly to pass from the egg to the adult stage from 14K to 91 davs. A tem- 

 perature ranging from 50° to 55° F. will either seriously check devel- 

 opment or kill large numbers of the immature stages of the fly. The 

 winter monthly mean temperatures of California and Florida are so 

 similar to those of the citrous regions of southern vSpain and Italy and of 

 Sicily that it is to be expected that the fruit fly, if introduced to the 

 mainland, would not become a serious pest to Citrus spp. It happens 

 that the very cold temperature necessary to bring citrous crops to that 

 degree of perfection in which they are most susceptible to fruit-fly 

 attack likewise renders the fly so inactive or sluggish that it may be 

 disregarded as a pest for that period of the year. 



In addition to the assistance of adverse climatic conditions during 

 that ])art of the year when they are most needed to protect citrous 

 crops, the growers of California and Florida are still further protected — 

 and most admirably so — from attack by the very scarcity of wild host 

 fruits that can not be destroyed. It will be found a practicable under- 

 taking to remove such a number of noncitrous host plants at present 

 697.33°— 15— 1 



