ORCHARD INSECTS OF THE PACIFIC NORTHWEST 23 



It feeds only on apple and on its alternate summer host, the plantain 

 or ribgrass. 



LIFE HISTORY 



The aphid passes the winter in the egg stage on apple trees, and the 

 eggs hatch in the spring when the buds begin to swell appreciably. 

 The young start feeding in the unfolding fruit buds, causing the leaves 

 to curl as they develop. Several generations are produced on the 

 apple, and these feed on the leaves and the fruit. Tightly curled leaves 

 often contain hundreds of the characteristically purplish or rosy-brown 

 aphids, and the species may be distinguished readily by its color and 

 by its habit of curling the leaves and deforming the fruit. As the 

 weather becomes warmer, brownish-green, winged individuals develop 

 and migrate to the plantain. Most of the aphids have left the apple 

 by early in July. Migration to other apple trees does not occur, and 

 trees not bearing winter eggs remain free of infestation. On the 

 plantain several generations of yellowish-green aphids occur, and in 

 the fall winged forms again develop and fly back to the apple trees, 

 where they produce a wingless generation of aphids which deposit 

 winter eggs on the twigs, in the axils of the buds, and in crevices in the 

 bark. These eggs are at first pale green but later become shiny black. 



CONTROL 



Control of the rosy apple aphid should be effected before the leaves 

 have been curled, as it is very difficult to accomplish afterward. As 

 aphids are sucking insects, contact insecticides rather than poisons 

 must be used. A spray containing 4 percent of oil destroys a great 

 many of the young aphids that are gathered on the buds if it is applied 

 just after the eggs have hatched. The dormant-season application of 

 lime-sulfur solution is relatively ineffective. More thorough con- 

 trol will result from using nicotine sulfate (40 percent nicotine) in 

 the proportion of three fourths of a pint to 100 gallons of water, in 

 combination with the oil emulsion or the lime-sulfur solution. This 

 application must be completed before the tips of the leaves have 

 begun to separate (fig. 25). 



Apple Aphid 



The apple aphid (Aphis pomi Deg.), formerly known as the green 

 apple aphid, lives on apple trees throughout the year and feeds mostly 

 on the succulent terminal twigs (fig. 26), curling the leaves and 

 stunting the growing shoots. It is thus injurious chiefly to nursery 

 stock and to young trees, although it sometimes becomes sufficiently 

 numerous on bearing trees to hinder normal growth. It is occasionally 

 found on pear trees. This aphid, which came from Europe, is now 

 found in the United States wherever apples are grown. 



LIFE HISTORY 



This aphid passes the winter in the egg stage, in the same manner as 

 the rosy apple aphid, although the eggs are more likely to occur on 

 water sprouts. The eggs hatch at about the same time as do those of 

 the rosy apple aphid, and there may be from 9 to 17 generations in a 



