EXPERIMENT STATION BULLETINS. 571 



•-one plant (in this case on the plum), while the young migrate to some 

 • other plant in the spring. The hop-aphis migrates from the plum to hop- 

 vines and passes the summer there. 



Aphids are sucking insects, taking their food through a slender tube 

 which is thrust deep into the tissue of the' plant. For this reason any 

 arsenical poison that may be deposited on the surface of the plant will 

 do them no harm; they will thrust their beaks clear through the 

 poison into the plant and will suck the sap from beneath the sur- 

 face. To kill these little robbers it is necessary to use contact poisons, 

 such as kerosene-emulsion, whale-oil soap, tobacco-water, Pyrethrum, 

 or some application which kills by closing up the pores or by irri- 

 tation, or else to use some vapor, smoke, or gas, such as tobacco- 

 smoke or carbon bisulphid. In exceptional instances, as in the case of 

 •lice that live underground, it is necessary to use some special treatment. 



APHIDS OF PLUM, CHERRY, AND APPLE. 



(Aphis prunicola, Myzus cerusi, Aphis mail.) 



During the spring and early summer, few days pass without bringing 

 some inquiry as to the method of getting rid of the lice on one of these 

 trees. As these three species of lice all yield to the same treatment, it 

 seems expedient to discuss them together. 



The apple-louse passes the winter in the form of an egg. These oval 

 eggs are very characteristic; they are black in color after they have been 

 laid for some time, and are usually crowded together in large numbers. 

 These are very difficult to destroy, and thus far nothing has been found 

 which will do any good without killing the tree as well. As soon as the 

 buds burst in the spring, the young lice crowd on to them and commence 

 to suck. They remain on the leaves for some time, but usually disappear 

 in the early summer to reappear again in the fall at the time of deposit- 

 ing eggs. 



The plum and cherry aphids differ in some respects, but the life-history 

 in general is similar. They may be easily killed by a spray of kerosene- 

 emulsion (Hubbard formula), diluting the emulsion ten times, or by a 

 spray of whale-oil soap, using one pound of the soap to six gallons of 

 water. In the case of the cherry-aphis it is best to apply it a little 

 stronger, as this louse is able to stand more than the others. Tobacco-tea, 

 made strong, is used by many with success, but whatever is used must 

 •"be applied thoroughly, for each louse must be hit to be killed. 



