CACTUS-FEEDING INSECTS AND MITES 49 



colony, the two or more groups each entering at a separate point on 

 the plant. In the fourth and fifth instar, at the one-half- to two-thirds- 

 grown stage, the breaking up of the original colony appears to be a 

 natural procedure; at this time the larvae issue from segments that still 

 contain a suitable food supply, and divide into from two to several 

 smaller groups. When full-grown the larvae make their exist from the 

 plant separately, drop to the ground, and find pupation sites. 



The shortest larval period of 27 days was secured in February and 

 March with an individual of the partial autumn generation. In the 

 summer generation the minimum duration has been 33 days, but 

 the average period is 50 days. In the winter generation the average 

 duration is 180 days, the larvae hatching in March and pupating 

 in September, but development from late-hatching eggs may be ac- 

 celerated and the larval period reduced to 120-130 days. 



The pupa is enclosed in a fine white silk cocoon which consists of 

 a loose outer covering and a more compact and closely woven inner 

 cocoon. Pupation sites occur among debris at the base of the plants, 

 between dead collapsed segments, inside dried eaten-out cladodes, 

 under stones, logs, and bark, and just beneath the surface of the soil. 

 The average length of the pupal (including the prepupal) period is 

 21 to 28 days during January and February and 35 to 42 days during 

 September-November. The minimum record is one of 1 3 days duration 

 in January, and the maximum is 90 days between early August and 

 early November. 



Parasites. — In Argentina the braconid Apanteles alexanderi is a common 

 enemy of Cactoblastis and Tticumania. Two ichneumons, Cryptus sp. 

 and Podogaster sp., have been reared from pupae of C. cactorum from 

 Entre Rios Province. 



Cactoblastis doddi Heinrich 



Although it was discovered in 1920, this species was confused with 

 C. hucyrus Dyar and hence remained unnamed until 1939. It is a native 

 of the more arid portions of western Argentina, the distribution ex- 

 tending tlirough the Provinces of Mendoza, San Juan, La Rioja, and 

 Catamarca to the northern section of Tucuman, and eastward into 

 the northwestern comer of Cordoba. Extensive investigations have 

 not revealed its presence in Santiago del Estero, although Opuntia 

 sulphurea, the usual host plant, occurs widely in that Province. Larvae 

 presumably representing tliis form have been found at Maimara in 

 the Province of Jujuy, while lar\'al tunnels in 0. sulphurea at Tapiza 

 in southern Bolivia suggest a further extension of its range. The dis- 

 tribution of C. doddi overlaps that of C. cactorum in the northern section 

 of the Province of Tucuman. 



263-417—68 5 



