MEXICAN FRUIT FLY -- A SITUATION REPORT 



First evidence that the Mexican fruit fly, a pest that prefers citrus but 

 attacks other fruits as well, had moved into southern California came the 

 second week in August when a live female fly was trapped in San Ysidro,San 

 Diego County. San Ysidro adjoins the Mexican city of Tijuana, Baja Cali- 

 fornia. 



Soon after the flv was found, the California Department of Agriculture 

 placed apart of San Diego County under quarantine. (See map.) No fruit 

 that might be infested by this pest can be moved from the area without the 

 approval of California Department of Agriculture plant pest control officials. 

 The quarantine action is one phase of the defense against the further spread 

 of the Mexican fruit fly. 



The discovery of the fly at San Ysidro was not surprising. Federal and 

 State control officials had been alert to a possible invasion since January, 

 when the first of several flies was discovered across the border near 

 Tijuana. Promptly following the initial finding in Tijuana, the United States 

 Department of Agriculture's Plant Pest Control Eranch, which was already 

 carrying on a cooperative control program with Mexico, concentrated traps 

 containing a lure on the Mexican side of the border. Similar action in co- 

 operation with California and Arizona Departments of Agriculture was inau- 

 gurated north of the border. Several flies were caught, most of them in 

 the Tijuana area. Others were trapped, however, across the border from 

 Calexico, Calif. , at the southern entrance to the Imperial Valley, and at 

 Ensenada, about 100 miles south of Tijuana. 



In the meantime, additional inspectors had been added to the plant 

 quarantine inspection staff at border ports of entry; pest survey work was 

 intensified on both sides of the border, and spray programs aimed at erad- 

 icating the pest were begun. 



Repeated surveys in the immediate areas where the flies were trapped 

 failed to reveal the presence of larvae. However, three empty pupal cases 

 were found in soil screenings, which indicated that some flies had gone 

 through at least part of their life cycle there. U.S. Department entomolo- 

 gists then assumed the presence of a light infestations in the border area. 



The mature Mexican fruit fly is considerably larger than the housefly. 

 The female has a sharp ovipositor about as long as its body. This needle- 

 like organ deposits eggs beneath the rind of the host fruit. Larvae hatched 

 from these egg clusters do the damage, feeding upon the fruit for about 6 

 weeks. Infested fruit shows premature color and breaks down internally as 

 the growing larvae feed. Heavily infested fruit usually drops to the ground 

 before the larvae mature. The larvae go underground to pupate and emerge 

 as flies. The fly can produce four generations a year or more under favor- 

 able conditions. 



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