CACTUS-FEEDING INSECTS AND MITES 51 



are truly gregarious. The cocoon is of rather stouter texture than that 

 of cactorum and is usually spun just beneath the surface of the soU, parti- 

 cles of which become mixed with the outer layer of silk. At pupation 

 time tlie larvae wander freely; dius the cocoons are not readily found, 

 as they do not occur in numbers at the base of, or in the immediate 

 vicinity of, the host plant. 



In the adult stage, males are rather more numerous than females, 

 the general average being approximately 48 percent females. Under 

 cage rearing conditions, however, the proportion of females is often 

 much lower, i.e., 34 to 38 percent. The females are almost as prolific 

 as those of C. cactorum; the following records furnish typical examples of 

 the average egg production: 



There are two generations annually, the adults emerging from late 

 January to early March and again in October and early November. 

 Emergence is less protracted than for C. cactorum, and is generally com- 

 pleted widiin 20 to 27 days at both seasons of the year; on occasion, 

 emergence of several hundred moths started and terminated within 16 

 days, both in October-November and January-February. The eggs 

 hatch in 26 to 32 days in October and November and in February 

 and March. The larval period occupies 5 to 6 weeks in midsummer; 

 in the winter generation the duration of the larval life is approximately 

 170 to 190 days. The pupal period in January and February varies 

 between 26 and 46 days, with an average of 35 days; in August- 

 October the time is longer, 49 to 67 days, the average being about 

 56 days. 



The larvae live in large colonies and tunnel through the host plant. 

 They are very destructive to 0. sulphurea, the plants of which are often 

 completely destroyed. Like C. cactorum larvae, they are comparatively 

 inactive during the height of winter, resuming active feeding for a 

 short period prior to pupation. 



Parasites. — The most common enemy is the braconid Apanteles 

 alexanderi. The tachinid parasite Epicoronimyia mundelli is of some impor- 

 tance. The chalcid Brachymeria cactoblastidis and an undetermined 

 ichneumonid are other pupal parasites. 



