HABITS. 19 



would deposit young thereon. The deposited young, because of 

 climatic and succulent food conditions, might become viviparous 

 instead of oviparous, causing a continuous increased infestation of 

 the hop vines. 



At Perkins and Santa Rosa, Cal., in 1912, a hot, dry wind early in 

 the season destroyed practically all of the aphides which came from 

 the alternate host, and it was the progeny of the later migrants 

 which became winged. 



These data have not been proven, but remain as the only explana- 

 tion of the presence of winged aphides between the spring and fall 

 migrations. 



Since the first insects that migrate to the hop are probably the 

 progenitors of the winged forms that occur during midsummer, it is 

 evident that the control of the aphis early in the season will tend to 

 reduce the numbers of the winged insects and therefore lessen the 

 chance that thoroughly sprayed yards will become reinfested. 



HABITS. 

 HABITATION. 



Hop aphides are usually found on the underside of the leaves 

 (PI. II, fig. 1), but in cases of severe infestation they may be found on 

 the upper surface as well. They gradually work up the vines, and 

 when the hops have formed many of them may be observed inside 

 of the cones. 



PROTECTION. 



Many of the aphides, especially in cases of slight infestation, will 

 be found close to the veins and in the hollow parts of the leaves. 

 Here, besides being protected by the sheltering leaf, they are partially 

 protected by the surrounding wall of leaf. Other than the natural 

 formations of the leaves the hop aphis has no protection from wind, 

 rain, or enemies. 



RELATION OF ANTS TO THE HOP APHIS. 



At Perkins, and especially at Santa Rosa, Cal., a large black ant, 

 Formica subsericea Say, was continually observed among the aphides. 

 The habit of the ants in caring for plant lice that they may feed 

 upon the honeydew excreted by them is historical. These ants 

 carry the aphides to the newly expanded leaves, thus spreading the 

 infestation. They were so active at Santa Rosa that it was found 

 necessary to put tree tanglefoot on the vines that were used for the 

 experiments, to prevent the ants from reinfesting them. 



