114 U.S. NATIONAL MUSEUM BULLETIN 256 



DIPTERA 



Only the Diptera that are primary enemies of cactus plants are con- 

 sidered in this publication. The many species of Syrphidae and Stra- 

 tiomyidae, whose larvae are scavengers or secondary enemies, following 

 up mechanical wounds, plant-disease lesions, and the injuries caused 

 by the primary cactus insects, are not discussed. 



The primary Diptera are restricted to several species of gall midges 

 of the family Cecidomyiidae, and two species of the muscoid family 

 Lonchaeidae. In view of the heavy crops of fleshy fruit produced by 

 prickly pears and other cacti, it is significant that no true cactus fruit 

 flies, family Trypetidae, have been discovered. There are a few records 

 of fruit flies having been reared from Opuntia fruit, but in each instance 

 a polyphagous species was involved. 



One incomplete observation of undetermined dipterous larvae 

 infesting prickly pear fruit was made at Anatuya, Province of Santiago 

 del Estero, Argentina. In February 1935 cream-colored larvae were 

 abundant in the fruit of Opuntia sulphurea and were found occasionally 

 in fruit of 0. utkilio. One larva occurred in the seed cavity of each 

 affected fruit, which became discolored and fell off before it ripened. 

 Sometimes the larva tunneled into the fleshy parts of the fruit. A very 

 high proportion, estimated at between 80 and 90 percent of the fruit of 

 0. sulphurea in the locality, contained larvae. Several pupated during 

 the same month but no adults were reared. 



DIPTERA: Cecidomyiidae 



Several species of gall midges have been reared from prickly pear 

 segments, but none appears to be of any importance. However, Asphon- 

 dylia opuntiae, which breeds in Opuntia fruit, has a definite controlling 

 effect, and is of unusual interest. 



ASPHONDYLIA Loew 



Three species of this large genus, A. betheli^ A. opuntiae, and A. arizon- 

 ensis, have been recorded from prickly pear. During the investigations 

 in the United States and Mexico, when particular attention was paid 

 to these fruit midges, one species only was encountered, and this 

 was invariably identified as A. opuntiae. A. betheli was described by 

 Cockerell in 1907 from prickly pear at Boulder, Colorado. A. opuntiae 

 was described by Felt in 1908. Through the courtesy of Professor 

 T. D. A. Cockerell, officers of the Board secured fruit of Opuntia torti- 

 spina infested with Asphondylia larvae from Boulder, the type locality 



