60 U.S. NATIONAL MUSEUM BULLETIN 256 



The newly hatched larvae are most active, wandering rapidly over 

 the prickly pear plants in search of young growth. For successful 

 breeding work, the provision of young segments of 0. aurantiaca was 

 essential. They seemed unable to penetrate the cuticle of older growth. 

 Under field conditions mortality among the young larvae must be 

 high, for during dry periods new growth may be absent or very limited. 

 Even where special attention has been paid to the question of pro- 

 viding the most suitable food supply in rearing cages, the proportion 

 of pupae obtained from the eggs has rarely exceeded 15 percent. 

 The average cocoon return from accommodated eggs during 18 

 generations in Argentina and Australia has been 12 percent, while 

 the highest figure in any one generation has been 30 percent in Argen- 

 tina and 29 percent in Australia. These results compare unfavorably 

 with those secured from C. cactorum, and indicate the normally high 

 mortality during the larval stage. 



The larvae are solitary and tunnel freely, often vacating one segment 

 to enter another. Although newly hatched larvae need to enter young 

 growth, older larvae are usually found in segments close to the ground 

 and may penetrate into the underground bulbs of 0. aurantiaca. It 

 has been observed both in Argentina and in Australia that a communi- 

 cation channel of webbing mixed with soil is often constructed from 

 the prickly pear segment into the soil for a maximum depth of several 

 inches, and that on hot days or when disturbed the larva retreats 

 underground; this habit has not been recorded among other cactus 

 phycitids. The frass is not discharged from the plant. One larva is 

 capable of destroying several segments of 0. aurantiaca and 0. discolor, 

 reducing the slender joints to thin shells. In large segments of 0. 

 inermis the damage is minor. 



The rather flimsy silken cocoons occur in the dry segments hollowed 

 out by the larvae, among debris, or just beneath the soil surface. The 

 duration of the pupal stage is generally from 12 to 17 days during 

 the summer months, November-March; the shortest recorded period 

 has been 10 days. The time increases to 30 days in autumn and to 

 90 days in winter; thus from a number of larvae that pupated in April, 

 the first moth emerged after 50 days and the last after 85 days. 



Owing chiefly to the irregular development of the larvae, the life 

 cycle varies considerably, even when the eggs have been deposited on 

 the same day. For example, in one lot of summer generation material 

 in Argentina, 90 moths emerged over a period of 54 days, from late 

 January until after the middle of March. The life cycle between March 

 and October is very inconstant; thus at Sherwood, Queensland, 

 eggs laid in February and March produced moths from late March 

 to the end of November, a variation of more than 8 months. The 



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