CACTUS-FEEDING INSECTS AND MITES 45 



The larvae are light orange, orange-red, or red, with conspicuous 

 transverse rows of black spots which tend to coalesce and so give the 

 appearance of cross bands. In all species the larvae are gregarious. 

 The eggs are laid in chains or eggsticks. The food plants are various 

 prickly pears (Platyopuntia), Cylindropuntia, Trichocereus, Echinopsis, 

 and Denmoza. The social habits and manner of working of the larvae 

 and the deposition of the eggs in long chains are duplicated in the 

 North American genus Melitara. 



Cactoblastis cactorum (Berg) 



This insect has won worldwide fame because of its role in the control 

 of the prickly pears Opuntia inermis and 0. stricta in Australia. First 

 introduced into Australia by the Prickly Pear Travelling Commission 

 in April 1913, it failed to become established. It was reintroduced in 

 small numbers in May 1925, and then reared and distributed in great 

 quantity. Within twelve years it solved this great weed problem of 

 Queensland and New South Wales. In approximately 30 million acres 

 that had been completely occupied by dense prickly pear, the pest was 

 destroyed by this insect, and in another 30 million acres of more scattered 

 infestations the pest was brought under control. The reclaimed land, 

 hitherto virtually valueless, has now been brought into agricultural 

 and pastoral production. 



C. cactorum occurs in the more northern Provinces of Argentina, in 

 Uruguay and Paraguay, and in the more southern portions of Brazil. 

 In Argentina it has been found in the Provinces of Entre Rios, Cor- 

 rientes, Santa Fe, the northern portion of Cordoba, Santiago del 

 Estero, Tucuman, Salta, Jujuy, and the Chaco; it has not been located 

 in the more arid western Provinces of Catamarca, La Rioja, and 

 Mendoza, where it is replaced by the allied species C. doddi; the dis- 

 tribution of these two forms overlaps in the Province of Tucuman. In 

 Uruguay, it has been recorded along the Uruguay and Plata Rivers 

 from Piriapolis in the south, northward to Salta. From Corrientes in 

 northeastern Argentina the distribution extends northward through 

 Paraguay, where the insect has been observed at Villa de Concepcion 

 and in the vicinity of Asuncion, into the Brazilian Province of Matto 

 Grosso, where larvae have been recorded at Corumba on the Paraguay 

 River. 



The range may include the southern Brazilian Provinces of Rio 

 Grande do Sul and Santa Catarina. In May 1937, at several places in 

 the former Province and at Florianopolis in Santa Catarina, newly 

 hatched to one-third grown larvae were attacking a Platyopuntia of 

 the Opuntia monacantha group. These larvae appeared to differ slighdy 



