Aj)ril, '11] • LOHRENZ: WOOLLY APHIS 167 



were thrown out in the field. Of 650 trees examined in the packing 

 house sixty were found with Aphis. This gives 9,2 per cent infested, 

 making a total of 11.2 per cent. 



NOTES ON FIELD OBSERVATION 



About the middle of June the Woolly Aphis was very numerous. 

 In some places from 20-25 per cent of the nursery stock was infested. 

 They were also very numerous on orchard trees of every age. About 

 the end of June the weather grew very warm and dry. As a result 

 the Aphis disappeared, not only the Woolly Aphis of the apple, but 

 many other kinds which had hitherto been very numerous. Very 

 close Search on older trees revealed a few on the shady sides under the 

 bark surrounding the scars. It is my opinion that many' of the 

 Aphis on the smaller trees and on the nursery stock descend dow^n to 

 the roots at the approach of the summer's heat. Later in the season, 

 as the temperature fell again, the Aphis increased in numbers, and in 

 September there were large colonies. These lasted until the cold 

 weather set in. 



Some of the infested nursery stock was sprayed with 15 per cent 

 kerosene emulsion. This killed the Aphis w^herever they came in 

 contact with the emulsion, but it is almost impossible to get the 

 emulsion into all the crevices, w^hich are the favored places of the 

 Aphis. Wherever the spraying was done properly the emulsion did 

 not injure the trees, but where too much was put on, it killed the 

 foliage. 



Several natural enemies were found to attack the Aphis. One 

 of the parasitic chalcis-flies killed off large colonies in the spring, and 

 for a while it was almost impossible to rear the Aphis in the laboratory, 

 because the parasite had been introduced with stock from the nur- 

 series. This enemy {Aphelinus mail Haldeman) was not found in 

 summer and in fall. 



In the spring there was also one of the lacewing-flies quite preva- 

 lent, the larvge of which lived on- the Woolly Aphis. The larvse of 

 a syrphus fly was busy not only in the spring, but also in the fall. 



NOTES FROM THE LABORATORY 



The Woolly Aphis of the apple has no great tendency to wander 

 about and seek new feeding grounds. This seems to be true especially 

 in the spring. At that time I had many apple twigs with Aphis 

 colonies, and in nearly every case the latter perished on the drying 

 twigs. .Observations during the month of November show that 

 they are a little more apt to wander in the fall. 



