336 SCIENCE FROM AN EASY CHAIR 



migrants produce wingless females on the plum tree. 

 They are followed to the plum trees by a final migrant 

 brood from the dying hops which are males the first yet 

 seen (Fig. 56). The males fertilise the wingless females 

 born on the plum tree and the latter lay each one 

 fertilised egg in the crevices of the bark of the plum tree 

 near the young buds. Winter now sets in : all are dead 

 except the eggs. In the following late spring a foundress 

 hatches out from each egg so deposited. The " foundress " 

 (Fig. 58) in this species, the hop aphis, is wingless. She 

 produces parthenogenetically and viviparously a brood of 

 wingless females. They similarly produce on the plum 

 tree a third generation of virgin females, but these have 

 wings! (Fig. 55). They fly back to the hop-vines, which 

 are now well risen from the ground and offer abundant 

 juice to the wingless virgin brood which escapes from the 

 winged migrants as soon as they have settled on the hop, 

 and feed and grow and produce new wingless broods 

 (Fig. 57) in rapid succession. 



The phylloxera of the vine is a plant-louse or aphis, 

 which exhibits an interesting adaptation of winged and 

 wingless broods to the requirements of the insect's nutri- 

 tion and multiplication. A " foundress " hatches from an 

 egg on the bark of the vine where it has passed the winter. 

 It proceeds to attack the young leaves and to produce a 

 brood of young. The leaves of the vine when thus attacked 

 swell up and produce galls, in which the young phylloxera 

 are enclosed, and there the phylloxeras continue to 

 multiply, producing more galls and thus destroying the 

 leaves. Some of the young broods now crawl down the 

 vine to its roots ; others stay on the leaves and continue 

 their destructive work there. There are several varieties 

 of form and size amongst these broods. Those which go 

 to the roots attack the rootlets and produce knobs and 

 swellings on them, leading to their destruction as feeding 



