CACTUS-FEEDING INSECTS AND MITES 141 



and the low-growing 0. inamoena in December 1928. The cultures 

 were numerous in many places and caused appreciable damage to the 

 younger growth of 0. palmadora. 



Cochineal insects of one species or another occur from the northern 

 portions of the United States to Argentina ; but investigations in several 

 regions where prickly pears flourish did not reveal their existence, viz., 

 Cuba, Venezuela, Curagao, northern Colombia, Ecuador, Honduras, 

 San Salvador, and Guatemala. However, the surveys conducted in 

 these areas were more or less hurried, and may have overlooked the 

 presence of these insects. The cochineal found in Peru was almost 

 certainly Dactylopius coccus, which may have been artificially established 

 in that country. 



HOST SPECIFICITY 



One of the curious features of cochineals is the range of host plants 

 in the genus Opuntia. As far as we are aware, no species of Dactylopius 

 is restricted to any one host plant. In fact each form attacks a variety 

 of prickly pears, including types that are not closely related. On the 

 other hand, cochineal insects exhibit varying degrees of preference for 

 or, at least, ability to thrive on, allied Opuntias. Their behavior 

 in this respect suggests that, in addition to recognised taxonomic 

 species, there are biological strains, or perhaps biological species. 

 The subject is discussed more fully, under the separate species, but 

 one point might be mentioned here: D. opuntiae on 0. lindheimeri in 

 Texas, and on various shrub pears from Texas to California, is con- 

 sidered to be identical taxonomically with D. opuntiae on 0. strepta- 

 cantha in Mexico. In Australia tlie Texas, Arizona, and California 

 strains of D. opuntiae could not be induced to attack 0. streptacantha, 

 but in Australia material on 0. streptacantha from Mexico readily 

 transferred to the same plant. 



ENEMIES 



In North and South America, wherever cochineals have been studied, 

 predacious enemies have exercised a very marked degree of control. 

 The relative scarcity of D. opuntiae in Texas and Arizona is almost 

 certainly due to the prevalence of various attacking insects. In Argen- 

 tina, where D. indicus and Dactylopius sp. near confusus occur freely, 

 and in Florida, where D. confusus is abundant, the cochineal infestation 

 is reduced periodically to light dimensions. 



Natural enemies include the adults and larvae of many species 

 of coccinellid beetles and larvae of several phycitid moths, of syrphid 

 and agromyzid flies, and of brown lacewings (Neuroptera) . 



