68 



leaves (seven hundred hills, 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 burning ; so that the issue from a single stem-mother may, under 

 favouring circumstances, blight hundreds of acres in the course of two or three months."* 



Fig. 38. 

 Winged male enlarged. 



The foregoing account of the life-history of the Hop Aphis is so wonderful and inter- 

 esting that we feel sure the readers of our reports will be glad to have it brought before 

 them. It is also of great value, as it enables hop growers now to apply remedies and use 

 methods of prevention that could not have been devised when the true habits of the insect 

 were unknown. 



The first and most obvious preventive measure is the destruction of the Aphis on the 

 plum trees in early spring before they have migrated to the hop. This can be done by 

 syringing the trees with a strong tobacco or soap wash, or more effectively still, by 

 using a weak kerosene emulsion. Receipts for making this were given in our report 

 for 1886, but for convenience sake we quote a simple method recommended by 



Professor A. J. Cook, of the Agricultural College of 

 Michigan ; he says : " I have found nothing so satis- 

 factory in treating plant-lice as the kerosene and 

 soap mixture. To make this I use one-fourth of a 

 pound of hard soap, preferably whale-oil soap, and 

 one quart of water. This is heated till the soap is 

 dissolved, when one pint of kerosene oil is added, 



/!// * /, -// and the whole agitated till a permanent emulsion or 



mixture is formed. The agitation is easily secured 

 by the use of a force pump, pumping the liquid 

 with force into the vessel holding it. I then add 

 water so that there shall be kerosene in the pro- 

 portion of 1 to 15.'"' This mixture has been found 

 most efficient as a remedy for plant-lice, and may be used against them wherever they 

 are found — upon the plum, or hop, or anywhere else. 



* We have to thank Dr. Riley for his kindness in permitting us to use the above illustrations of the 

 Hop-Aphis. They were orginally drawn by him to illustrate his paper on the subject in "Insect Life." 

 vol. i., pp. 133-136. 



Fig. 39. 



Eggs and shrivelled skin of female 



which laid them, enlarged. 



