THE PHYLLOXERA OF THE VINE i6i 



which enlarge at successive moults until the fore pair project 

 far beyond the body ; the hind pair are shorter and narrower ; 

 both are delicate and transparent, like the wings of an Aphis, 

 but lie flat over the back when at rest, instead of being 

 erected. The Phylloxera of this second stage can fly, but its 

 migration is probably due to transport by wind as much as 

 to its own exertions. After the flight, by which the important 

 advantage of dissemination in fresh localities is gained, the 

 winged insects come to rest, and each lays about four eggs 

 on the leaves, buds, and bark of the vine, or in the surface 

 soil above the roots. These eggs are of two sizes ; the larger 

 ones produce females, the smaller ones males of the third 

 form or stage. 



In this third stage, and here only, individuals of different 

 sex appear. The true males and females are developed rather 

 late in the season, and possess neither wings, beak, nor 

 alimentary canal. Being unable to feed, they last only a 

 few days. The female, after being fertilised, lays one 

 enormous winter-egg, which is generally attached to the bark 

 of the vine by a hooked spine, and is protectively coloured. 

 The winter-egg hatches in spring, and there issues from it 

 a female, differing a little in shape and size from the first 

 form; this is distinguished as the "stock-mother." She may 

 produce parthenogenetically — i.e. without fertilised eggs — gall- 

 forming insects, which infest the leaves, and after one or more 

 generations, lay unfertilised eggs, from which root-infesting 

 Phylloxera of the first type proceed, or she may produce 

 root-infesting forms only. The gall-forming Phylloxera may 

 be distinguished from the other by wanting the tubercles on 

 the skin, which are found on the adult root-parasites. In 

 America the gall-formers appear to be regularly developed in 

 considerable numbers, while the root-infesting form is less 

 frequent ; in Europe the gall-formers are often not developed 

 at all, so that they cannot be considered as essential stages 

 in the life-history. 



The cycle may be shortly summarised as follows : — 



1. Parthenogenetic, wingless, suctorial females, chiefly (in 

 Europe) infesting the roots, but also making galls on the 

 leaves. There are several generations of these. 



2. Parthenogenetic, winged, suctorial females, which lay 

 two kinds of eggs, .from which are hatched : 



