320 



Journal of Agricultural Research 



Vol. III. No. 4 



Fig. I. — Cross section of peach, showing egg 

 cavity of the Mediterranean fruit fly with 

 eggs. Drawing made directly after oviposi- 

 tion. Original. 



leaving the eggs well separated and with ample room, making conditions 

 favorable for the newly hatched larvae. (See figs, i and 2.) On the other 

 hand, in citrous fruits no such enlargement of the egg cavity takes place. 

 Instead there occurs a general hardening of the walls of the cavity, and 

 the eggs remain as tightly packed as when deposited. In many instances 



the cavity walls become almost woody. 

 In fact the egg cavities in all the thicker 

 skinned citrous fruits, such as grape- 

 fruit, lemons, and sweet oranges, re- 

 semble a gall the cavity of which is filled 

 with eggs and the opening more or less 

 clogged with a yellowish substance 

 from the ruptured cells, and in Hawaii 

 still further sealed by exudations of 

 gummy secretions, especially in certain 

 grapefruit, limes, and lemons. These gall-like cavities in the rind do not 

 share in the general withering of the rind that takes place in citrous 

 fruits after they have been picked for some days, but stand out from 

 the general surface as small nodosities. (See fig. 3.) It is usual in host 

 fruits of the fruit fly for the punctured surface to develop a depression. 

 These tliickened and often woody walls of the cavity no doubt offer an 



obstacle to the lar%'ae reaching the 



rest of the fruit which they can not 

 overcome; hence, the larvae are 

 forced either to die in the cavity itself 

 or to work their way out through 

 the opening of the puncture to the 

 surface of the fruit. It is probably 

 seldom that lan.'^ leave the fruit by 

 way of the opening of the puncture, 

 but a few newly hatched larvas have 

 been found by the writers with their 

 bodies half way out of the fruit. 



Larvae that succeed in getting out 

 of the cavity must burrow through 

 the rag before reaching the pulp, and 

 this is a difficult task, as evidenced 

 by the fact that out of 3,345 newly hatched larvae that succeeded in 

 reaching the rag, as shown in Table I,' 3,276, or 97.9 per cent, died in 

 the rag. The larvae, after leaving the egg cavity, burrow in all directions, 

 but seldom get more than i inch from the cavity and usually not that far. 

 Often they are able to reach the skin covering the pulp or to burrow 



FiG. 2. — Cross section of peach, showing the gen- 

 eral shriveling of the walls of the egg cavity and 

 the separation of the eggs. Drawing made i'4 

 days after oviposition. Original. 



' This number excludes shaddock No. i and sour and Chinese oranges, which are of no commercial value 

 and are more easily infe.ted than grapefruit, lemons, limes, and sweet oranges. 



