The Hop Aphis. 289 



winged parthenogenetic females continue to be developed in about the proportion 

 of one to a hundred wingless individuals until about picking time. 



Autumnal History. — After the hops were picked and the pistillate plants were 

 practically all dead, above ground, the male plants were kept under observation 

 for three weeks. The lice continued to develop and increase materially in numbers 

 upon tliese plants, yet only an occasional winged specimen was developed, as was 

 true during the summer, and these were all parthenogenetic females. By the end 

 of August or early in September the male hop plants were also all quite dead 

 above the ground, and in many instances the yards had been closely pastured off 

 by sheep Before this had occurred, however, an occasional wingless oviparous female 

 aphid was observed, and also a number of winged males ; and these were always 

 found on the lower leaves and runners of the male hop vine. 



These egg-laying females differ in appearance but slightly from the females 

 previously described, yet on examination under the microscope the eggs in them 

 can be quite readily discerned. The winged males are the offspring of wingless 

 parthenogenetic motliers. These differ from those aphids previously described 

 in being rather slimmer and longer, and in being marked with black dorsally ; the 

 whole color-effect of the bodies of these males being darker than is the case 

 with the others. 



We were unable to actually find the eggs of the hop aphis in any of the yards 

 under observation, nor upon any of the neigliboring vegetation, but the wingless 

 egg-laying females being produced on the male hop vine only is good presumptive 

 evidence that the eggs are deposited there. Tlie male hop plants on which the 

 aphids were first found in 1903 were, in tlie majority of cases, the same plants 

 on which they were found at the end of the preceding season, and in the few cases 

 where these last infested vines were not the same that were first infested they 

 were near neighbors of these vines. Our observations have been continued iuto 

 the present year, 1904, and the same liolds true, the same vines being again the 

 first to show the presence of the hop aphis, and from them the trouble has again 

 spread. 



Wintering. — The California data given above seem to indicate that the hop 

 aphis hibernates in some situation in the hop yard itself in the egg form. The 

 eggs may be placed either upon the cut stalks of the hop vines at or just beneath 

 tlie surface of the ground, or upon the roots of the plant, or even in the ground 

 contiguous to the vines. At no time have we been able to find any evidence of 

 the presence of the hop aphis on any other vegetation near to or in the hop yards. 

 This fact, coupled with their appearing first upon the same male plants year after 

 year, or at least in the same parts of the yards, and their continuance upon these 

 plants until the very end of the season, points strongly to the probability of 

 hibernation taking place in the suggested situations. That wingless oviparous 

 females and winged males are to be found upon these late-growing male vines, and 

 that these are the last forms of the aphids to be produced in the hop yards, would 

 seem to add weight to the idea of hibernation occurring in the egg form in the 

 hop yard itself. 



HISTORY ELSEWHEEB. 



The insect has an entirely different history elsewhere, and gave rise to many 

 conflicting theories by students of this interesting insect before the full life- 

 history was worked out. Probably the most complete study that has been made 

 was published by the late Prof. C. V. Riley, then entomologist of the United States 

 Department of Agriculture. This account appears in the report of that depart- 

 ment for 1888. Briefly this life-history, as given by Prof. Riley, is as follows : 

 "Hibernation takes place on different varieties and species of primus (plum), and 

 the little, glossy, black, ovoid eggs of the species are found attached to the 

 terminal twigs, and especially in the more or less protected crevices around the 

 buds. From this winter egg there hatches a stem-mother, which is characterized 

 by being somewhat stouter, with shorter legs and honey-tubes than in the indi- 

 viduals of any other generation. Three parthenogenetic generations are produced 



HOR. 19 



