420 THE INVERTEBRATA 



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 Euonymus. 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. The repro- 

 ductive capacity of these insects is most remarkable and is fortu- 

 nately offset by the number of enemies which they possess. 



The following summary will assist in the understanding of the life 

 cycle of Aphis rumicis : 



Fertilized eggs laid in autumn 



I 

 Viviparous parthenogenetic females > Euonymus 



I 

 Winged migrant parthenogenetic females 



I 

 Wingless parthenogenetic viviparous females \ 



I \f r Viciafaha 



I Winged viviparous females (autumn) J 



Winged males x Wingless oviparous females \ 



\ \ Euonymus 



Eggs laid in autumn J 



Though the order contains insects for the most part harmful to 

 man and his property, a few are useful in that they yield the dyestuffs 

 Kermes (females of Kermes ilicis) and Cochineal {Dactylopius coccus), 

 and the resin stick-lac {Tachardia lacca). The usually harmful 

 plant-sucking habit is being put to good use in Queensland where the 

 coccid bug, Dactylopius tomentosus, is employed against the prickly 

 pear cactus with considerable success. 



Order EPHEMEROPTERA (Mayflies) 



Vestigial mouth parts reduced from the biting type; wings mem- 

 branous with a reticulate venation ; the hinder pair small ; caudal fila- 

 ment and cerci very long (Fig. 311). The nymphs are aquatic and 

 an active winged stage known as the subimago occurs before the last 

 moult yields the adult. 



The eggs are laid in water, either scattered over the surface or 

 attached to stones, etc., by the female, which enters the water for the 

 purpose. 



