46 U.S. NATIONAL MUSEUM BULLETIN 25 6 



from those of C. cactorum. Two eggsticks, containing 121 and 110 eggs 

 respectively, were observed; the individual eggs seemed to be of larger 

 diameter than typical C. cactorum material. This form would almost 

 certainly be C ronnai, described from moths reared from larvae in 

 spineless cactus in Rio Grande do Sul. In view of the wide distribution 

 of C. cactorum and of its occurrence in Uruguay, Argentina (Corrientes) , 

 and Paraguay, adjoining to the south and west the two Brazilian 

 Provinces, it seems probable, however, that the southern Brazilian 

 insect will pi'ove to be cactorum. 



The host plants are various species of Platyopuntia, with Cleistocactus 

 sp. the one exception. This rather slender Cereus is occasionally 

 attacked in localities in Santiago del Estero, Argentina, where the 

 insect is abundant in various prickly pears. Cerei and other types of 

 cacti which occur freely in northwestern Argentina are otherwise 

 immune from attack. The host prickly pears in South America include 

 the following: 



Tree pears: 0. Jicus-indica, 0. cordobensis, and young plants only 

 of 0. quimilo. 



Shrub pears: 0. brunnescens, 0. monacantha, 0. canterai, 0. delaetiana, 

 0. bonaerensis, and various similar forms of the monacantha-bonaerensis 

 group. 



Narrow-jointed pears: 0. salmiana, 0. utfiilio, 0. discolor, 0. auran- 

 iaca, 0. retrorsa, and others of the aurantiaca group. 



In fact, the insect breeds in all species of prickly pear within its 

 range of distribution, with two rather notable exceptions. The tree 

 pear 0, quimilo, a frequent plant in northwestern Argentina, appears 

 to be avoided, except in tlie case of young plants, which are often 

 destroyed by the larvae. The low-growing 0. sulphurea, a plant with 

 broad thick segments which is very common in Santiago del Estero 

 and Tucuman Provinces in areas where C. cactorum is prevalent, has 

 not been recorded as a food plant. This prickly pear is the usual host 

 plant of Cactoblastis doddi. 



In Australia C. cactorum freely attacks the North Am.erican shrub 

 pears 0, inermis and 0. stricta and the tree pear 0. streptacantha. In 

 the Mexican tree pear 0. tomentosa the larvae develop quite readily 

 under cage conditions, but in the field the moths do not oviposit 

 on this species except on very young plants, a circumstance analogous 

 to that of 0. quimilo in Argentina. 



The insect occurs generally, and often abundantly, throughout its 

 range of distribution. In February 1924 every prickly pear plant 

 around Concordia, Entre Rios, harbored colonies of larvae. It was 

 again common in this vicinity, as well as around Paso de los Libres, 

 in June 1937 and in 1958. Larvae were numerous in shrub prickly pears 



