CACTUS-FEEDING INSECTS AND MITES 121 



is not rare. From one to several segments or from one to six fruit may 

 develop; as many as 10 fruit have been observed growing from one 

 infested example. These new fruit, which are quite normal, mature 

 before the end of summer. Although it may have acquired the growth- 

 producing function, the affected fruit invariably falls off after emer- 

 gence of the adult midges. On one occasion, near Hext, Texas, two 

 fruit growing from an infested fruit were themselves attacked by 

 Asphondylia. This phenomenon was observed in 1928, a season in which 

 emergence was prolonged over a period of several weeks; it could 

 not have happened in a normal year. 



Despite the fact that the incidence of segments and fruit from infested 

 fruit is common in 0. lindheimeri and 0. cacanapa, it has been recorded 

 with only one other Opuntia; in California affected fruit of 0. vaseyi have 

 produced both segments and fruit. This growth-forming peculiarity 

 of the fruit has never been observed among the 0. engelmannii-phaea- 

 cantha group of host plants in western Texas to Arizona; in the 0. torti- 

 spina forms in Texas, Colorado, and other places; in 0. littoralis and 0. 

 covillei in California; in 0. inermis and 0. stricta in Australia; or in 0. 

 cantabrigiensis, 0. hyptiacantha, and 0. imhricata in Mexico. 



Concerning the importance in control, since all seeds in an infested 

 fruit are rendered sterile, the potential value of this insect in reducing 

 the natural spread of prickly pear is very great. However, in most 

 districts where Asphondylia is well distributed, areas showing a heavy 

 percentage of fruit infection are scattered or are localized. Thus, one 

 may encounter plants and even stands of prickly pear with 90 percent 

 fruit infection, and yet in the same district the vast majority of the 

 plants shows no trace of attack. The midge is of real importance on 

 the central-western plateau of Texas in the region lying between 

 Rocksprings, San Angelo, Brownwood, and Austin, where the degree 

 of fruit infestation is very high and very general. It is considered that 

 the sporadic occurrence of prickly pear in the Ballinger-Brownwood- 

 Lampasas country may be due to the large-scale destruction of the 

 seeds by this insect. On the other hand, it has been reported that 

 infested fruit of 0. lindheimeri can produce as many as 12 normal fruit. 

 If this condition were general, the midges would assist the spread of 

 prickly pear through the increase in the quantity of seeds yielded by 

 each plant; but, actually, the number of additional fruit produced in 

 this manner does not nearly counterbalance the proportion of seeds 

 rendered incapable of germination. 



In some instances, the attack by Asphondylia supplies favorable 

 conditions for the entrance of plant disease organisms. Around Del 

 Rio, Texas, in April 1928 the anthracnose fungus Gloeosporium lunatum 

 was active in 90 percent of the fruit from which the midges had just 



