118 U.S. NATIONAL MUSEUM BULLETIN 25 6 



and falls off. The life cycle occupies 12 months, of which at least 11 

 months are spent in the larval stage; the pupal period is 5 to 10 days. 



A prime consideration involved in the experiments toward the 

 possibility of establishing this insect in Australia was that the adiolt 

 midges must emerge in September and October, concurrently with the 

 flowering of prickly pear, instead of in March and April as in North 

 America. This objective was attained by shipping the infested fruit 

 from Texas as soon as they showed the characteristic signs of attack. 

 Material dispatched in April, about four weeks after the eggs were 

 laid, reached Australia in May, and yielded adult midges from mid- 

 September to the end of October. Thus, the life cycle was shortened 

 from the normal 12 months to approximately 6 to 7 months. It should 

 be pointed out that the larvae left Texas in the spring and arrived 

 in Australia at the beginning of the Southern Hemisphere winter; 

 hence, the larvae were not subjected to summer heat, either in North 

 America or in Australia. The acceleration of the life cycle by subject- 

 ing the young larvae to comparatively cool climatic conditions, instead 

 of the normal hot summer, is a matter of considerable interest. 



On the other hand, cold temperature experiments with older larvae 

 in North America arrested or retarded development. Material placed 

 in storage at 39° F. early in February, before the larvae had entered 

 the rapidly-growing stage, showed no appreciable growth after an 

 interval of 3 months. Again, infested fruit placed in early February 

 in a cool vault, where temperatures were variable but considerably 

 below atmospheric readings, were retained at the cooler conditions 

 for 103 days; the adults emerged in June, 23 days after removal of the 

 fruit from the vault and 2K months later than emergence in the field. 



The life history has been studied at Uvalde, Texas, both in the field 

 and under cage conditions. Emergence of adults in various years in 

 the Uvalde district occurred as follows: 



1922. In the second half of March. 



1923. The only record was made on April 15. 



1925. Commenced on March 12, and was general until March 30; 

 a few adults appeared in early April. 



1926. Commenced on March 9, reached the peak on March 22, 

 and was almost complete by March 3 1 . 



1927. March 15 to 31. 



1928. At Uvalde commenced on March 20, and 25 miles south 

 of Uvalde began on March 15. At Del Rio, 80 miles west of Uvalde, 

 commenced on March 1. Continued until middle of April. 



1929. Commenced on March 8; about 50 percent had emerged 

 by March 3 1 ; continued until middle of April, 



