32 BULLETIN 536, U. S. DEPARTMENT OF AGRICULTURE. 



oil-cells, hence the immunity of lemons is due chiefly to the imperviousness of the rag 

 and the gall-like developments about the egg cavity which make it difficult for the 

 hatching larvae to leave the cavity. 



In the laboratory a comparison was made between the infestation of the rind of 

 cured California lemons and well-grown fruits picked fresh, both green and yellow 

 in color, from the trees. About the egg cavities in freshly picked fruits infested by 

 adults in the laboratory, a hard, more or less gall-like condition of the walls and ad- 

 joining tissues develops rapidly. In the well-cured fruits no such gall-like harden- 

 ings were detected following infestation, and after hatching the larvae had little 

 difficulty in working their way out of the puncture into the rag. Thus six California- 

 grown lemons such as are found on the markets were exposed between April" 3 and 

 5, 1915, in large glass jars containing each about 200 flies. After removal they were 

 held until April 12, when an examination showed them to have been oviposited in 

 16, 26, 31, 29, 39, and 20 places, respectively. Of the 161 punctures, only 8 had been 

 made in, or through, an oil-cell and in these the ft cayitata (numbering, respectively, 

 2, 1, 1, 3, 0, 2, 5, and 8) were dead. From the remaining 153 punctures, made between 

 the oil-cells, 441 larvae had escaped into the rag beneath, where, without exception, 

 they were found dead. Other well-grown but greenish colored lemons were gathered 

 from the trees and immediately exposed to adults within similar glass jars between 

 April 14 and 16, 1915. These fruits were examined April 19-20. Before being 

 exposed in the jars all punctures in the rind, made previously in the field, were 

 covered with gummed paper. Th.e results of the examination of two of these fruits 

 are given here as typical: 



Fruit No. 1. 



Puncture 1. One dead larva in puncture located between oil-cells. 

 2. One unhatched egg in puncture in oil-cell. 

 33. Three unhatched eggs in puncture between oil-cells. 



4. Six unhatched eggs in puncture between oil-cells. 



5. Two larvae barely alive in rag beneath puncture made between oil-cells. 



6. Five unhatched eggs in puncture between oil-cells. 



7. Seven unhatched eggs in puncture between oil-cells. 



8. Four unhatched eggs in p mcture between oil-cells. 



9. Six dead larvae in puncture between two oif-cells. 



10. One dead larva in punctr n, ° between two oil-cells and one dead in rag 

 close by. 

 11-19. These nine punctures were shallow and contained nothing. 



Fruit No. 2. 



Puncture 1. Nine dead larvae in rag beneath puncture between oil-cells. 



2. One dead larva in puncture made between oil-cells. 



3. Four dead larvae in puncture made between oil-cells. 



4. Three unhatched eggs in puncture made between oil-cells. 



5. One dead first-instar larva in rag beneath puncture made between oil- 



cells. 

 These data indicate the way citrus fruits are protected from infestation of the 

 pulp, and they supplement previously published data on the development of larvae 

 within lemons. 



23. Grapefruit. x 



The ordinary types of grapefruit which have come under the observation of the 

 writers have been particularly resistant to attack up to the time when they are fit 

 for table use as indicated by the data of Table VIII. These data were secured dur- 

 ing September. Many fruits from these trees in Manoa Valley, Honolulu, which 

 were sufficiently ripe to fall to the ground, have been held over sand in the labora- 

 tory but yielded no adult flies. The writers have found other trees bearing fruits 

 with rinds of a looser texture from which they have reared adults, and in certain 

 instances have found fruits still attached to the trees, which, though much overripe, 

 were badly infested. It seems very probable, therefore, that should the fly reach the 

 citrus regions of the mainland, certain thin-skinned varieties of grapefruit might 



