742 Rospert MATHESON 
The summer host plants 
For many years the summer host plants have been searched for in 
vain. It remained for Ross (1915) to first record his successful transfer 
experiments to the broad- and narrow-leaved plantains (Plantago major 
and P. lanceolata). He states also that this species was reared thruout 
the summer on apple where crowding was prevented. 
The experiments of the writer prove that at Ithaca the narrow-leaved 
plantain, or rib grass (P. lanceolata), is the preferred summer host plant 
and also in all probability the necessary summer host plant. In numerous 
experiments this species of lice could be reared on P. major for only two or 
three generations, when the line would die out, due to unknown causes; 
whereas under similar conditions the insects would continue to thrive on P. 
lanceolata. The results of these experiments are in accord with the work 
of Baker and Turner (1916 b), tho not with that of Ross (1915 and 1916) 
and of Brittain (1915b). The more important reasons for believing 
that P. lanceolata is the necessary host plant, and that only here and there 
has this species of lice acquired the ability to use P. major, have already 
been pointed out in the historical discussion. Of course it is very probable 
that owing to the adaptability of Aphis sorbi and the abundance of 
Plantago major, the insect may eventually use either summer host plant 
without any marked preference as shown at present. 
Ross’s statement that this aphid can maintain itself thruout the season ff 
on apple is very important. Unfortunately, his statement is not sup-ff 
ported either by the work of Baker and Turner (1916 b) or by that of the 
writer, tho Brittain (1915 b and 1916) records experiments in which he 
carried the species thru the summer on apple in Nova Scotia. This 
important phase in the life cycle of this species needs more investigation, 
for should the species become able to thrive on apple thruout the season 
it might become a pest of the first magnitude. 
The summer forms 
The spring migrants, after settling down on the plantain, begin pro 
ducing living young within two or three days. All of their immediat 
descendants are wingless viviparous females. The young congregat 
about their mothers and are commonly found on the underside of th 
lower leaves, at the base of young, tender leaves, or on the developin 
