288 Appendix. 



pound ; whale-oil soap, 7 cents per pound. The labor and the expense of a horse 

 were the same as in the first described experiment. Figuring from this basis we 

 find the cost of spraying with this material to be somewhat less than with the 

 kerosene emulsion and tobacco decoction, amounting to between .$4.50 and $5.00 

 per acre for the season's work. The aphids were well controlled by the spraying 

 with this material in this yard, and no loss was caused by them here. Again, 

 the near-by hop vines and yards not treated had the value of their product 

 reduced fully one-half by the aphids. 



The experimental work in these two yards indicated that both the extract 

 of quassia and the tobacco decoction were effective in destroying the aphids. 

 They did not, however, spread out over the leaves in a satisfactory manner when 

 used alone. It was also shown that neither the kerosene emulsion nor the solution 

 of whale-oil soap, at the strength at which it was safe to use them, were alone 

 suflficient to effectively control the aphids. By combining the tobacco decoction 

 with the kerosene emulsion, or the quassia extract with the whale-oil soap, the 

 insecticidal value of both materials is fully utilized and the spreading of the liquid, 

 so necessary for satisfactory work, is accomplished. 



Though many other spray materials were experimented with, none of them 

 controlled the aphis nearly so well as the two above described. 



Probably the ease of obtaining either the tobacco waste or the quassia chips, 

 and the cost of these ingredients of the spray at the time when purchased, will 

 determine which of the two materials is to be used by the hop-grower. 



In the treated yard the yield in hops in 1903 was about 1,700 pounds per 

 acre, and in the untreated yards the yield was on the average only 900 pounds 

 on the same area. The fact that by treatment such as has been indicated 

 growers have been able to double the returns'^on each acre of hops amply proves 

 that careful spraying for the hop aphis pays well. 



DESCRIPTION AND METHOD OF GEOWTH OF THE HOP APHIS. 



In our California yards the first hop aphids to appear in the spring, as 

 mentioned above, are wingless females, which produce living young parthenogenet- 

 ically ; that is, without the male aphids being present. These were probably 

 produced from eggs in which the insect had passed the winter, and correspond 

 with what is called the "stem mother." These females when full grown are from- 

 one and one-half to two millimeters (one-eighteenth to one-twelfth of an inch) in 

 length. They vary in color from very pale green to dark green. They are provided 

 with rather long antennae set on frontal tubercles, which are toothed internally. 

 The first joints of the antennae are similarly toothed. This character of the 

 frontal tubercles and first antennal joint serves well to identify the species. The 

 honey-tubes or nectaries which are located on the distal portion of the abdomen, 

 one on either side of the medial line of the dorsum, are quite prominent. The 

 young are similar in appearance to the adults, but are smaller. The mother aphids 

 produce their young at the rate of from four to six a day, and specimens kept 

 under observation by us continued this rapid production of young for twelve days. 

 A total of sixty-six young were produced by some of these females. These young 

 aphids in their turn begin to reproduce their kind on about the fourth day after 

 their birth. The rapid increase in the numbers of the aphids found upon the hop 

 vines in infested fields is easily understood when we consider the rapidity of 

 reproduction shown by these creatures. 



In from two to three weeks after these wingless parthenogenetic females first 

 appear, winged aphids will occasionally be found. These differ from the first 

 chiefly in having two pairs of relatively large wings, which are quite delicate in 

 structure and almost transparent. The fore wings are much larger than the hind 

 wings, and both are rather sparsely veined in a manner characteristic of the 

 group. These winged aphids, which produce living young in the same manner as 

 do the wingless ones, first described, fly sufiiciently well to spread the attack to 

 other vines. Thus in a very short time what was at first a local infestation of 

 small moment may become an attack involving large areas of the hop yard. The 



