HOMOPTERA 



normal, functional legs and are capable of movement over the host-plant 

 although the amount of movement by these forms is usually not great. 

 Jn fact some of the tortoise scales are practically fixed. 



The division into motile and non-motile forms is a purely artificial 

 one used for the sake of a clearer understanding of these important insects. 



The cottony-cushion scale, Iccrya purchasi. — This beautiful insect 

 (Fig. 200) was at one time the most dangerous insect pest in California, 

 and did a great amount of injury. It is an introduced Australian species, 

 and has been subdued to a great extent by the introduction of an Aus- 

 tralian lady-bug, Rodolia cardinalis , which preys upon it. The body of 

 the adult female is scale-like, dark orange-red, and has the dorsal surface 

 more or less covered with a white or yellowish-white powder. The insect 

 secretes a large egg-sac, which is beautifully ribbed. 



Fig. 200. — Icerya purchasi. 

 and young, on orange. 



Females, adult 



Fig. 201. — Orthezia, enlarged. 



Orthezia. — The 



■ Pseadococcus longi- 

 enlarged. 



threads like wool. 



members of this genus occur not uncommonly on 

 various weeds. They are remarkable for the 

 calcareous secretion with which the body is 

 clothed. This is in the form of long plates. Fig- 

 ure 201 represents a nymph; in the adult female 

 the secretion becomes more elongated posteriorly, 

 and forms a sac containing the eggs mixed with 

 a fine down. Later, when the young are born, 

 they remain in the sac till they have themselves 

 secreted a sufficient amount of the lamellar mat- 

 ter to cover them. 



The mealybugs. — The mealybugs are com- 

 mon pests in greenhouses all over this country, 

 especially the long-tailed mealybug, Pseudococcus 

 longispinus (Fig. 202). In California there are 

 several species which live in the open and become 

 serious pests to citrus trees. Mealybugs excrete 

 a white waxy material which may be in the form 

 of a white powder over the body or of white 



