CACTUS-FEEDING INSECTS AND MITES 53 



Mexican States of Sonora, Chihuahua, Neuvo Leon, as far as San 

 Luis Potosi. It was found in almost every district throughout this 

 extensive territory where Cylindropuntias occurred, abounding in 

 many places, notably the Big Bend country of west Texas, in southern 

 New Mexico, and in southern California. Heinrich records specimens 

 from localities in the southeastern comer of Nevada. 



The food plants are various Cylindropuntias; other hosts have not 

 been observed. Throughout its range in Mexico, Texas, New Mexico, 

 and Colorado, Opuntia imhricata, the dominant Cylindropuntia of this 

 region, is selected. Other plants known to be attacked are 0. whipplei 

 in Utah, 0. echinocarpa, 0. serpentina and 0. parryi in California, and 

 0. spinosior, 0. arbuscula, and 0. acanthocarpa in Arizona. Thick-jointed 

 species such as 0. prolifera and 0. Julgida seem to be avoided, while 

 the slender-jointed 0. leptocaulis does not appear to be a host plant. 



The larvae are wholly white or grey-white and are solitary in habit. 

 They infest the terminal segments and the fruit. The larva enters the 

 fruit a little to one side of the crown and later tunnels through into the 

 segment. It is thought that the newly hatched larva attacks the flower 

 head. The entrance hole in the fruit is not kept open, shows no webbing, 

 and is marked by a dark spot. The fruit turns yellow on one side, then 

 somewhat black, and finally dries up, it remains attached to the seg- 

 ment but is easily detached, since there is no webbing. When fruit 

 are absent the larva enters a terminal segment near its apex; in this 

 case the entrance hole is kept open and is surrounded by a certain 

 amount of webbing in which pellets of frass are mixed. As the larva 

 develops the segment may wither completely. Damage to the plant is 

 rarely of greater extent than the destruction of occasional apical joints, 

 but, if the larvae are numerous, many segments may be killed. The 

 insect is of greater importance as a fruit enemy. Many instances have 

 been reported in which more than 50 percent of a heavy fruit crop on 

 large plants has been destroyed. 



Unlike most cactus phycitids, the larva of C ponderosella does not 

 vacate the plant to pupate, nor does it form a proper cocoon. The pupa 

 lies free within the larval excavation; a pad of loose silk around the 

 head suggests an unfinished cocoon. It is usually located at the apical 

 end of the infested segment near the larval entrance hole. In the fre- 

 quent cases where the larva has not maintained an opening, the 

 emerging moths must push off the loosely attached dead fruit. 



The adult has a wing expanse of 1 )^ inches and is rather more slender 

 in appearance than the various species of Olycella, Melitara, and Cacto- 

 hlastis. The forewings are grey with two long and several shorter 

 black longitudinal lines; the hindwings are white. The white eggs are 

 deposited singly on the spines of the host plants. 



