HOMOPTERA 



449 



period begins v^aries greatly. Thus, while in the mealy-bugs the 

 cocoon is made during the second stadium, in Icerya it is not made till 

 near the end of the third. In the Diaspidinse the formation of the scale 

 begins either at the close of the first stadium or immediately after the 

 first molt. With the molt at the beginning of the quiescent period 

 the male loses its legs, antennae, and mandibular and maxillary setae. 

 The setae are not replaced; and, consequently, the adult males can 

 take no food. The legs and antennas of the adult are developed from 

 histoblasts, as in insects with a complete metamorphosis; the wing- 

 buds appear in the last nymphal stadium; but they are developed 

 externally, as in insects with a gradual metamorphosis. The type of 

 metamorphosis of the male coccid is, therefore, neither strictly com- 

 plete nor gradual. This illustrates the difficulty of attempting to 

 make sharp distinctions; for in nature all gradations exist between 

 the different types of structure and of development. 



The classification of the CoccidcE. — The different writers on the 

 Coccidae have grouped the genera into a variable number of sub- 

 families. In the classification by MacGillivray ('21), this author 

 recognizes seventeen subfamilies, and gives two tables for separating 

 them, one based on the characters presented by the first nymphal 

 instar, and one on those of adult females. Tables are also given for 

 separating the genera and species of the different subfamilies. 



The following are a few of the better-known representatives of 

 this family found in this country. Several subfamilies not mentioned 

 here are represented in our fauna. 



Subfamily MONOPHLEBIN^ 



The Giant Coccids 



The common name of this family 

 was suggested by the large size of 

 many of the exotic species. The 

 best-known species found in North 

 America is of moderate size; this is 

 the cottony-cushion scale, Icerya 

 pUrchasi (Fig. 524). The adult fe- 

 male measures from 4 to 8 mm. in 

 length, is scale-like, dark orange- 

 red, and has the dorsal surface more 

 or less covered with a white or yel- 

 lowish white powder. It secretes a 

 large, longitudinally ribbed egg-sac, 

 which is white tinged with yellow 

 This beautiful insect was at one time 

 the most dangerous insect pest in 

 California, and did a great amount of 

 injury. It is an introduced Austra- 

 lian species, and has been subdued 



Fig. 524.- 

 adults, 



-Icerya purchasi: females, 

 and young on orange. 



