146 U.S. NATIONAL MTJSEUM BTJLLETm 25 6 



a vascular bundle, and that the tissue immediately surrounding the 

 apex of the organ dies and becomes filled with a pink substance. 

 It is thought that the action of cochineal is toxic in character and is 

 carried from the point of attack through the plants by the vascular 

 system. 



Vigorous plants of prickly pear are often able to resist the attack 

 by forming a layer of cork around the insect's proboscis. This develop- 

 ment must either cut through or at least injure the delicate organ 

 to bring about the death of the insect. 



Dactylopius coccus Costa 



In January 1 929 cultures of a large-bodied cochineal were found on 

 . ficus-indica at Tarma and Huanuco, Peru; this record is held to repre- 

 sent the above species. No other observations were made of the existence 

 of cochineal in Peru and Ecuador. 



It seems strange that D. coccus has not been discovered in our exten- 

 sive field work in Mexico and other prickly pear areas. The species is 

 established in South Africa on the spiny prickly pear, an 0. streptacantha 

 type of which the identification is uncertain. The usual host plants of 

 the commercial cochineal are Nopalea cochenillijera and 0. ficus-indica. 

 In Australia (1921-1930) it was reared successfully on 0. tomentosa. 



Dactyhpius opuntiae Lichtenstein 



This form attacks prickly pears throughout Mexico and in the southern 

 portions of Texas, New Mexico, and Arizona. In the northern parts 

 of Texas, New Mexico, and Arizona, and northward through to 

 Kansas and Wyoming, D. confusus appears to be dominant, but it 

 is possible that the range of D. opuntiae overlaps that of D. confusus. 

 On the gulf coast of Texas, D. opuntiae is found from Brownsville 

 north to Victoria, but has not been observed in the vicinity of Galveston. 



On the whole, cochineal is not prevalent in the southern United 

 States, although it occurs in all districts from the Texas coast to the 

 Californian coast. The extensive fields of 0. lindheimeri in Texas are 

 often free from infestation; occasionally, however, the insects become 

 numerous in local areas. The same remarks are true of New Mexico 

 and California, but in southern Arizona this species occurs more 

 generally. In Mexico the distribution extends from the northern 

 border to Oaxaca in the south; the species is found freely and often 

 in great abundance on the Central Plateau at such points as Aguas- 

 calientes, San Luis Potosi, and Queretaro. 



The host plants include practically all species of Platyopuntia 

 growing within its range and are mainly shrub pears in the United 



