752 BKroRT — 1887. 



7. The eleventh or twelfth generation will produce winged females (from the 

 middle to the end of August), which will deposit their young upon the Plum ; and 

 these will become the only sexed iudi\'iduals of the year — the male winged and the 

 female wingless, the latter after coition consigning a few impregnated or- winter- 

 eggs to the twigs. 



8. At the date of writing (August 5th) the first females on Hop were still alive 

 and breeding, having existed two months. There is, consequently, an increasing 

 admixture of generations from the first on Hop until frost overtakes the species in 

 all conditions and sweeps from the hop-yards all individuals alike, perpetuating in 

 the egg state those only which reach the sexual condition on the Plum. 



9. Each parthenogenetic female is capable of producing on an average one hun- 

 dred young (the stem-mother probably being more prolific) at the rate of One to 

 six, or an average of three per day, under favourable conditions. Each generation 

 begins to breed about the eighth day after birth, so that the issue from a single 

 individual easily runs up, in the course of the summer, to trillions. The number of 

 leaves (700 bills, each with two poles and two vines) to an acre of Hops, as grown 

 in the United States, will not, on the average, much exceed a million before the 

 period of blooming or burring ; so that the issue from a single stem-mother imaj, 

 under favouring circumstances, blight hundreds of acres in the course of two or 

 three months. 



10. While meteorological conditions may materially affect the increase and 

 power for mjury of the species, these are far more truly predetermined and 

 influenced by its natural enemies, many of which have been studied and will be 

 described. 



11. The slight colorational differences, as also the structural differences, includ- 

 ing the variation in the cornicles on head and basal joints of antennaj, whether 

 upon Plum or Hop, are peculiarities of brood, and have no specific importance what- 

 ever. 



12. The exact knowledge thus gained simplifies the protection of the Hop-plant 

 from Phorodon attack. Preventive measures should consist in destroying the 

 insect on Plum in early spring where the cultivation of this fruit is desired, 

 and the extermination of the wild trees in the woods wherever the Hop interest is 

 paramount ; also in avoiding the introduction of the pest into new Hop countries 

 in the egg state upon plum cuttings or scions. Direct treatment is simplified by the 

 fact that the careful grower is independent of slovenly neighbours, infection from 

 one hop-yard to another not taking place. 



Experiments still under way have shown that there are many effective remedies, 

 and that the ordinarj' kerosene emulsion diluted with 25 parts of water and 

 sprayed with the cyclone nozzle ; or a soap made by boiliiig 1 lb. of pure potash 

 in 3 pints of fish oil and 3 gallons of water, and tbis dissolved in S gallons of water, 

 and sprayed in the same way — are thoroughly effectual remedies, and leave the plant 

 uninjured. The former costs 75 cents, the latter 30 cents, per acre, plus the time 

 of two men for three hours, plus appliances. The object of further'experimentation 

 now being carried on is to simplify and reduce the cost of Ihese last to a minimum. 

 As they consist, however, essentially of a portable tank and a force pump with hose 

 and spraying attachment which, together, need not involve a greater first outlay 

 than jS'o to ^10, and as every American Hop-grower can afford to expend the larger 

 sum for the protection of a single acre, there is no longer any excuse for allowing 

 this pest to get the better of us. 



It is not my purpose, however, to enter into aphidicide details in this commu- 

 nication, which I will conclude by brief reference to the bearings of these 

 discoveries in America on the problem in Great Britain. The most comprehensive 

 and satisfactorv review of the knowledge possessed on the subject in England that 

 has come to my notice, is that by my esteemed friend and correspondent, Miss 

 Eleanor A. Ormerod, consulting entomologist of your lloyal AD:ricultural Society, 

 in her 'Report of Observations of Injurious Insects,' &c., made in 1885. So far 

 as her own careful observations are concerned they fully accord with the facts 

 here set forth ; but on the authority of others, and especially on the evidence of 

 Mr. C. "NV hitehead, who reported finding young lice and large viviparous females on 



