INSECTA 



479 



these eggs hatch, giving wingless parthenogenetic females which 

 produce young viviparously. A variable number of these partheno- 

 genetic generations is passed through in the summer and then winged 

 parthenogenetic females occur which migrate to another host (the 

 bean or other plants), and there reproduce, giving rise to generations 

 of parthenogenetic females which eventually produce winged females 

 which migrate back again to the primary host, the spindle tree Euony- 



Fig. 331. External anatomy of Leptocoris trivittatus with wings spread on 

 one side. After Essig. an. antenna; he. hemielytron. 



mus. This generation gives rise to oviparous females which copulate 

 with winged males, migrants from the secondary host plant. 



In other forms, such as Phylloxera vastatrix, the notorious pest of 

 vineyards, the life history is immensely complicated and involves 

 migrations between root and stem of the host plant. The reproductive 

 capacity of these insects is most remarkable and is fortunately offset 

 by the number of enemies which they possess. 



