740 RoBEeRtT MATHESON 
the number of generations of the latter that were reared. In the spring 
of 1915 the main migration at Ithaca consisted of the adults of the fourth 
generation, tho a large proportion of the third generation also migrated 
to the summer food plants. In 1916 there was only a slight infestation 
about Ithaca and practically all of the third generation consisted of the 
winged migratory forms. 
The factors which influence the early or late production of migratory 
forms have not been suggested by any worker. The necessity of investi- 
gating the influence of climatic factors is urgent. As has already been 
pointed out, this is a very interesting problem to the biologist, and to the 
fruit grower it is one of paramount importance. In 1915 there was a 
serious outbreak of Aphis sorbi in New York State and the amount of 
damage done was very great. This was largely due to the fact that 
a comparatively small proportion of the third generation produced 
migrants. As a result the enormous numbers of the third generation 
produced young at a very rapid rate, resulting in the most serious infesta- 
tions. The writer saw an orchard which, about the early part of June, 
showed only the usual marginal infestation in the lower branches. In this 
case the third generation (young) was appearing in large numbers and it 
was thought most of them would become migrants. For some unknown 
reason scarcely any of these produced winged forms, and as a result the 
trees became so infested that scarcely a leaf or a fruit could be found 
that was not crowded with the lice. When this generation (the fourth) 
became nearly mature there was not sufficient nourishment for them 
and they migrated in thousands to the branches and trunks, while th 
ground under the trees was literally swarming with them. As this orchar 
was well cultivated, the majority of the aphids died, tho thousands reache 
maturity and migrated to adjacent fields where the narrow-leaved plantai 
was growing in abundance. In this one small orchard the owner estimate 
his loss at from $800 to $1000. If the factors involved in the earl 
or the late production of the winged migrants could be determined 
this would be a Jong step in solving some problems in insect control. 
There is another important point which cannot be overlooked at thi 
time. Ross (1915) reports that he succeeded in rearing this species thruou 
the season on apple in Ontario, Canada, tho he presents no definite data 
If this condition should become prevalent, there would be an instane 
