ARTHROPODA 



305 



promised at one time to destroy totally the orange industry. The Australian 

 ladybug, which keeps it within bounds in its native home, was imported, and the 

 increase of the ladybugs was such that the cushion-scales were all but destroyed. 

 This species of ladybug feeds exclusively on the cottony-cushion scale, and there- 

 fore the destruction of the latter led in turn to the rapid decline of the ladybugs 

 from the loss of their food supply. Indeed it was necessary to keep colonies of 

 the scale insects protected in order to furnish food and to prevent the entire 

 destruction of the imported beetle by starvation. In Australia where both are at 



FIG. 148. 



FIG. 148. Swallow-tail Butterfly (Pafiilio machaon), larva, pupa, and adult. From Nicholson. 



Questions on the figure. Which is the larva and which the pupa? Which 

 of these is the earlier stage? What are the chief characteristics of the three stages 

 in the metamorphosis of butterflies, the larva, the pupa and the imago? 



home the natural conditions and the adjustment of the two species are such that 

 this scale-insect does not become a pest. The discovery of the biological relations 

 of these species, and the relief of the orange industry furnish a sample of the ex- 

 cellent work being done by the U. S. Department of Agriculture in connection with 

 the economic aspects of biology. 



Order Hymenoptera (membrane-wings}. Hexapoda with four membranous 

 wings; mouth appendages adapted for sucking or for biting; metamorphosis com- 

 plete. This is the most highly developed division of Insecta, and embraces such 



