APPLE INSECTS 



151 



The Apple Bud-aphis 



Siphocoryne avence Fabricius 



This green aphis is the one which most commonly infests the 

 opening apple buds in the United States and Canada. It is 

 an old European species, which has a very wide range of food- 

 plants, including apple, pear, hawthorn, quince, plum, at least 

 seven other trees, five weeds or herbs, 

 wheat, rye, oats and nine different 

 grasses. It is most injurious to the 

 apple, often nearly covering the open- 

 ing leaf -buds and blossoms, and it 

 sometimes injures young wheat in 

 the fall. 



The yellowish-green, wingless, vi- 

 viparous stem-mothers hatch from the 

 shiny, black, oval winter eggs as soon as 

 the apple buds begin to open, and most 

 of their progeny develop into winged 

 parthenogenetic, blackish females (Fig. 

 163) which leave the apple in May. A 

 few may remain on the trees through 

 two or three more generations, or 

 until July. In 1893 we found that 

 these spring migrants could be readily colonized on June and 

 meadow grasses (species of Poa), and we succeeded in following 

 the insect through thirteen parthenogenetic generations on these 

 grasses from late in May until November. Then some developed 

 into the winged return migrants, but others continued to breed 

 and finally lived through the winter on these grasses and on 

 wheat kept under outdoor conditions. Curiously enough, all the 

 generations grown on the grasses were alternately wingless and 

 winged viviparous females. They were much smaller and 



P^iG. 163. — The apple bud- 

 aphis, a parthenogenetic fe- 

 male with wing pads. 



