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



ripened when infested show none of the usual signs of attack until 

 the larvae have begun to work. It is due to this failure of fruits to 

 record their infestation by some external sign, other than the incon- 

 spicuous puncture, that so much fruit is purchased as sound in the 

 markets, or shipped from orchards, or taken on board ships. 



As the larvae hatch and begin their work of destruction within the 

 host, the signs of infestation increase rapidly. The sunken areas 

 about the punctures of tender-fleshed fruits may increase until the 

 entire fruit has a collapsed appearance. 



In all fruits well infested within there is a "give" to the area be- 

 neath the puncture, indicating destroyed tissues beneath. In hard- 

 fleshed fruits such as some varieties of apples (PI. XI, fig. 2), pears, 

 and quinces there may be no external evidence of larval work except 

 a ring of dark decay about the puncture, and yet the outer portion of 

 the pulp alone may be unaffected. Peaches are often thoroughly 

 infested within and still maintain their normal shape and give evi- 

 dence of infestation only by a dull and slightly darkened color of the 

 skin. A hole in the rind, no larger than the lead of a pencil, from 

 which juice exudes when the fruit is compressed, may be the only 

 indication of infestation in oranges and grapefruit, although rings of 

 decay usually develop in infested citrus fruits containing numerous 

 larvae. Fruits of the elengi tree (Mimusops elengi), which have an 

 orange shell-like exterior (PI. VIII, fig. 2), may appear normal, but 

 on being broken open are found to be literally packed with well- 

 grown larvae. It is never possible for the average man to examine 

 casually any host fruit and state conclusively that it is not infested. 



METHODS OF SPREAD. 



There are numerous records on file which demonstrate clearly 

 the methods by which the Mediterranean fruit fly is spread, not only 

 between widely separated countries, but about land areas. The 

 development of rapid transit and cold storage and the increase in 

 tourist travel have been the greatest factors in dissemination in more 

 recent times. Geographical isolation is no longer a protection 

 against introduction, as has been proved almost monthly by the 

 interception of fruit flies at the ports of entry of the United States 

 by the agents of the Federal Horticultural Board. 



SHIPS. 



The unrestricted consignments of fruit and ships' stores have 

 been responsible for much of the spread of C. capitata between coun- 

 tries. MacLeay, as early as 1829, records the importation at 

 London of cargoes of oranges from the Azores that contained larvae, 

 and Middleton, in- 1914, states that in the same city hundreds of 

 larvae and pupae are imported every j^ear from Spain and destroyed 



