The Mexican fruit fly infests both grapefruit and oranges, but shows a 

 strong preference for grapefruit. Lemons, interestingly enough, are too 

 sour. In Mexico it also attacks such deciduous fruits as peaches, pears, 

 and apples. Its favorite subtropical hosts are mango, white sapote, and the 

 wild yellow chapote. 



LONG A NUISANCE FOR TEXAS CITRUS 



While this is the first known appearance of the Mexican fruit fly in Cal- 

 ifornia, citrus growers in the Rio Grande Valley of Texas have known it well 

 since 1927. Beginning very late in the fall or in the winter, the fly moves 

 into the valley from its native northeastern Mexico to infest the grapefruit 

 and orange groves. Few other host plants grow in the valley. The infesta- 

 tion usually reaches a peak in March or April, then disappears by early 

 summer after the citrus crops are harvested. Because of the new invasions 

 each year, eradication in the Rio Grande Valley is impractical. 



TEXAS LOSSES COMPARATIVELY LIGHT 



The Mexican fruit fly usually causes comparatively light damage in 

 Texas, in part because of the absence of certain wild fruits that serve as 

 reservoirs of infestation in some parts of Mexico, in part because of the 

 lack of a succession of favored cultivated fruits, and in part because the 

 citrus crop is harvested each season usually before the pest has a chance 

 to build up a heavy infestation in the crop through successive generations. 



Texas citrus growers, however, are required by quarantine regula- 

 tions to apply a vapor-heat treatment to much of the fruit, especially grape- 

 fruit, after infestations have been found, to prevent the pest from spreading 

 to other fruit-growing areas. The treatment, devised by U.S. Department 

 scientists, kills any overlooked larvae or unhatched eggs. As a rule this ex- 

 tra handling of the fruit costs more than the damage done by the insect, and 

 becomes an additional marketing expense. Under some conditions of fruit- 

 handling processes, the vapor-heat treatment has been reported to cause 

 some damage to the fruit. 



DIFFERENT IN CALIFORNIA 



If the pest should become established in northwestern Mexico and south- 

 ern California, both U.S. Department and California control officials believe 

 that losses would be much greater than those sustained in Texas, because 

 conditions in California are more similar to those in Mexico where the fly is 

 most destructive. 



Unlike the Rio Grande Valley, California produces citrus the year around 

 and grows a wide variety of other fruits, such as apples, pears, and peaches, 

 that might prove attractive to the pest. Valencia oranges in particular could 

 support a fruit fly population at a time when the pest normally is building up 

 to a peak infestation. Valencias mature in May but often stay on the trees 

 through late fall awaiting a favorable market. 



