PHYLLOXERIDJE. 67 



The European representatives of the genus Phyl- 

 loxera were limited about fifty years ago to one single 

 species, named by Boyer de Fonscolombe Phylloxera 

 quercus. This author mentioned the insect as feeding 

 on Quercus pubescens and Q. cocci/era. His observa- 

 tions on the insect were correct, and I can establish 

 the evolution of the species as follows : 



1. Egg deposited in the bark crevices of Quercus 

 coccifera. 



2. Foundress, or Pseudogyna fundatrix, feeds on the 

 same tree. 



3. Pseudogyna migrans, as larva and nymph, feeds 

 on the same tree, but after getting wings emigrates 

 to Quercus pubescens. 



4. Pseudogyna gem/mans feeds under the leaves of 

 Quercus pubescens. 



5. Pseudogyna pupifera feeds, as larva and nymph, 

 on the same tree ; but after getting wings flies back 

 to Quercus coccifera to deposit on the leaves the pupae 

 out of which the males and females issue. 



6. These last, after union, deposit their single egg 

 in the bark crevices, where it passes the winter. 



When I first published the above observations many 

 able entomologists doubted their correctness ; but 

 shortly after me Prof. Targioni Tozzetti, of Florence, 

 found that the same cycle of life occurred in another 

 species of Phylloxera, that is to say, Phylloxera 

 florentina, Targioni. This insect is born on Quercus 

 ilex, the evergreen oak, and passes the summer on 

 Quercus sessilijlora. 



Thus, two species of Phylloxera have been proved 

 to migrate from the deciduous to the evergreen oak ; 

 but, as the ilex group is a southern species, it is 

 probable that neither Phylloxera quercus nor P. 

 florentina occurs in Great Britain. 



The following four species appear to undergo their 

 whole biological evolution on Quercus robur or its 

 varieties : 



