DRYOBIUS CROATIOUS. 77 



tliat the insects named by him D. rohoris are really 

 D. Groaticus of Koch. But Mr. Walker's description 

 in the 'Ann. of Nat. History' is very obscure, and 

 the sense of the latter part involved. Koch does 

 not appear to make any very marked distinctions in 

 his diagnosis between the two species, but they amount 

 to this, that the insects differ in their general tones 

 of red, and the form of brocading on their wings. He 

 states that his description and figure of D. Groaticus is 

 borrowed, but he does not say from whom. He notes 

 that the eggs of D. rohoris are deposited on twigs, 

 peduncles of leaves, and on fruit capsules (" Trieben, 

 Blattstielen, Fruchtkapseln "). 



The tinctorial character of some Aphides has been 

 before noticed. The English specimens of B. Groaticus, 

 in a very marked degree, stain Canada balsam, disul- 

 phide of carbon, alcohol, &c., of a fine port-wine red. 

 I do not notice this peculiarity in the examples of 

 D. rohoris sent me by M. Lichtenstein. 



Lichtenstein adds another reason for believing D. 

 rohoris and Groaticus distinct, viz. that the males vary 

 as to their wings, and that the sexual forms of the 

 former appear about a fortnight later in the autumn 

 than the latter. 



In France the egg of B. Groaticus laid on Quercus 

 ilex hatches in April, and the mother Aphis produces 

 young which assume wings and then they migrate, 

 but to what tree it does not appear. Lichtenstein 

 thinks they go to Quercus rohur and Q. puhescens, and 

 that they eventually come back again to the ilex. 



In countries like England, where Quercus ilex is not 

 indigenous, we must suppose there is some modifica- 

 tion both of food plant and nidus, for oviposition. 



The genus Dryohius does not appear to be repre- 

 sented in America by any described species. Wherever 

 the common Oaks of the old world, Quercus rohur, Q. 

 pedunculata, and Q. sessiliftora are found, the Aphides 

 peculiar to these trees may pretty generally be met 

 with. Although these trees extend over the whole of 



