414 



AN INTRODUCTION TO ENTOMOLOGY 



with it. This honey-dew is fed upon by bees, wasps, and ants. The 

 bees and wasps take the food where they find it, paying Uttle if any 

 attention to its source ; but the ants recognize in the plant-Hce useful 

 auxiharies, and often care for them as men care for their herds. 

 This curious relationship is discussed later, under the head of Ants. 

 In addition to honeydew, many aphids excrete a white waxy sub- 

 stance. This may be in the form of powder, scattered over the 



Sc^R^M+Cu,^lstA 



Fig. 489. — The wings of Eriosoma americana. (From Patch.) 



surface of the body, or it may be in large flocculent or downy masses; 



ever}^ gradation between these forms exists. 



The superfamily Aphidoidea includes two families, the Aphididas 



and the Phylloxeridas. These two families differ in the life-histories 



of their species and in the venation of the wings of the winged forms, 



as follows : 



A. Only the sexually perfect females lay eggs; the parthenogenetic forms give 

 birth to developed young, which, however, in some cases, are each enclosed in a 

 pellicle. The radius of the fore wings is branched; and the outer part of the 

 stigma is bounded behind by vein Ri (Fig. 489) Aphidid^ 



AA. Both the sexually perfect females and the parthenogenetic forms lay eggs. 

 Vein Ri of the fore wings is wanting; and the outer part of the stigma is 

 bounded behind by the radial sector (Fig. 490) Phylloxerid.,e 



Sc^R^M^Cu 



+ istA 



Fig. 490. — The wings of Adelges. (From Patch.) 



