CACTUS-FEEDING INSECTS AND MITES 119 



It is evident that the temperature and atmospheric conditions that 

 stimulate the after-winter growth and flowering of prickly pear 

 influence both the rapid development of larvae at the end of the winter 

 and the emergence of the adult midges. For example, at Del Rio in 

 1928 midge emergence was 3 weeks earlier than at Uvalde, and the 

 flowering of prickly pears in the vicinty of Del Rio showed approxi- 

 mately the same period of advancement. In 1926 interesting records 

 were made of the effect of temperature on the emergence of adults 

 from field-collected fruit. Emergence commenced on March 9; until 

 March 18 the daily number of midges varied between and 36; during 

 this period shade temperatures varied between 54° and 79° F. max- 

 imum, and 37° and 57° F. minimum. Thereafter the following data 

 were secured: 



26-31 55-70 35-50 153 



Thus, of 1658 midges that emerged in the period March 9-31, 1222, 

 or almost 75 percent, appeared during the 5-day period, March 20-24, 

 inclusive, of relatively high temperatures. 



In addition to observadons at Uvalde, emergence has been noted at 

 other localities as follows: 



Marathon, western Texas: mid-March 1925. 



Navidad River, eastern Texas: March 25, 1928. 



Boulder, Colorado: May 2-3, 1925. 



Mormon Lake (7000 ft.), northern Arizona: June 9, 1925. 



San Luis Potosi, Mexico: March 2, 1928, about 50 percent had 

 emerged. 



Aguascalientes, Mexico: Emergence had commenced on March 

 11, 1928. 



Tehuacan, southern Mexico: First week of March 1927. 



The appearance of adults from one fruit usually extends over several 

 days, and even over 12 days in extreme cases. The time of emergence 

 varies considerably. At Uvalde, in March 1925, 75 percent of the 



