214 



INSECTS AFFECTING FIELD CROPS 



recommended for cabbage maggot, page 232, can be well used 

 against onion maggots, which closely resemble cabbage maggots 

 in appearance and life history. 



INSECTS AFFECTING HOPS 



The Hop Plant Louse (Phorodon humuli Schr.). The hop 

 louse, which was introduced from Europe about the time of the 

 Civil War, is light green in color. The summer is passed on the 

 vine and both winged males and females migrate to plum trees in 

 the fall, where wingless females are produced and fertilized by the 

 males. Eggs are then deposited upon the twigs of plum and in 

 axils of buds. The " stem-mothers " hatch from these eggs in the 

 spring, giving rise to two or three broods of 

 wingless viviparous females (Fig. 229) before 

 winged migrants are produced. The mi- 

 grant flies to the hops and continues to 

 bring forth females asexually until the fall. 

 In warm parts of the country it has been 

 shown that this louse may remain the entire 

 year on the hop, and some may stay on the 

 plum during the summer. 



It will be noted that in a general way 

 this aphis follows the same general rule, as 

 regards reproduction, that is observed in 

 connection with other plant lice. For 

 further information on the reproduction of 

 In - plant lice, see page 14. 



Injury. This is probably the most seri- 

 ous pest of hops. The hop plant louse not only draws the sap 

 from the vines, but by exuding a "honey dew," which drops to 

 the leaves below, coats the surface of the leaves with a glistening 

 film, which affords an excellent medium for the growth of a fungus, 

 giving to the vines a dark, blighted appearance. 



Control. Where this pest is abundant, spraying with whale-oil 

 soap, quassia chips, or with tobacco extract gives relief if done 

 thoroughly and before the lice become too numerous. After the 

 leaves are curled as a result of their attack, it is much more diffi- 

 cult to hit them with a spray. A solution of quassia chips is made 

 by soaking eight pounds of chips in sufficient water to cover them, 

 for a few days; then boil for about one hour; add one hundred 

 gallons of water and five pounds of whale-oil soap. If the latter 



FIG. 229. Hop-plant 

 louse, female. (From 

 sect Life.") 



