[66 



THE STUDY OF INSECTS. 



poisonous gas (hydrocyanic-acid gas) is generated within the 

 tent. 



A number of useful insects belong to this family. Several 

 species furnish dye-stuffs. The best known of these is 

 Coccus cacti, the dried bodies of which are known as Cochi- 

 neal. The stick lac of commerce, from which shell-lac or 

 shellac is prepared, is a resinous substance excreted by 

 a species, Cartcria lacca (Car-ter'i-a lac'ca), which lives on 

 the young branches of several tropical trees, and the bodies 

 of these insects, which are obtained from the stick lac, furnish 

 the coloring agents known as lac dye. China wax is another 

 substance for which we are indebted to this family. It is the 

 excretion of an insect known as Pe-la, Ericcrns pe-la (E-ri- 

 ce'rus). In fact many species of this family excrete wax in 

 considerable quantities. 



Among the more prominent members of this family are 

 the following : 



The Cottony-cushion Scale, Icerya purcliasi (I-ce'ry-a 



pur'cha-si). — This beautiful in 

 sect (Fig. 203) was at one time 

 the most dangerous insect 

 pest in California, and did a 

 great amount of injury. It is 

 an introduced Australian spe- 

 cies, and has been subdued to 

 a great extent by the intro- 

 duction of an Australian Lady- 

 bug, Vcda/ia (V e-da.'\i-a) y which 

 preys upon it. The body of 

 the adult female is scale-like, 

 dark orange-red, and has the 

 dorsal surface more or less 



Fin .203.- Icerya purchasi Females, adult COV ered with a white Or yel- 

 and young-, on orange, (From the Author s J 



Report for 1880.) lowish-white powder. The in- 



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

 The Mealy-bugs, Dactylopius (Dac-ty-lo'pi-us). — The 



