April, ’18] 
BECKER: WOOLLY APHIS 
249 
Table III 
Exp. No. 
Duration of 
Experiment 
Trans 
No. 
'ers 
Total Aphids 
Applied 
Results 
• 
Ca-Cl. 
7/2-10/15 
1 
5 
Colony 
Oa-C2. 
7/2-11/1 
1 
5 
Colony 
Ca-C3. 
7/2—8/5 ' 
6 
30 
Colony 
€a-C4. 
7/6—8/7 
9 
45 
Colony 
Ca-C5. 
7/18-8/1 
9 
45 
None established 
Ca-C6. 
7/18-8/1 
10 
50 
None established 
€a-C7. 
7/18-8/1 
10 
50 
None established 
Ca-C8. 
7/18-7/21 
2 
10 
Established 
Ca-C9. 
7/18-7/21 
3 
15 
None established 
Ca-CIO. 
7/18-8/1 
10 
50 
None established 
Ca-Cll. 
7/18-8/1 
10 
50 
None established 
Ca-C12. 
8/1-8/17 
12 
60 
None established 
€a-Cl3. 
8/1-8/17 
9 
45 
None established 
Ca-C14. 
8/1-8/17 
11 
55 
None established 
Ca-C15. 
8/1-8/17 
9 
45 
None established 
Ca-C16. 
8/1-8/17 
9 
45 
None established 
Ca-C17. 
8/3-9/14 
6 
30 
None established 
Ca-Cl8. 
8/3-8/15 
1 
5 
One established 
Ca-C19. 
8/3-9/14 
12 
60 
None established 
Ca-C20. 
8/3-8/15 
1 
5 
Five established 
Ca-C21. 
8/3-9/14 
5 
25 
None established 
Ca-C22. 
8/3-9/14 
14 
70 
None established 
Ca-C23. 
8/3-9/11 
5 
25 
None established 
Ca-C24. 
8/23-9/14 
1 
5 
Colony 
€a-C25. 
8/23-9/14 
2 
10 
None established 
€a-C26. 
8/23-9/14 
7 
35 
None established 
From these experiments and from our general experience with the 
species we conclude; 
(1) That through being continuously subjected to the attacks of the 
woolly aphis Crataegus has acquired a strong immunity against this 
pest. 
(2) That this immunity is inherent or it may be conditional, de¬ 
pending upon factors which influence the character of its growth. 
Experiments in Transferring Crataegus Aphids to Apple and 
Vice Versa 
As early as 1910 Hay hurst, thinking that there might be two races 
of lanigera, one on apple and one on Crataegus, made attempts to es¬ 
tablish the Crataegus forms on apple and vice versa. His results were 
all negative. The writer repeated the experiments in 1911 with the 
same results and in 1913 Mr. Quick, a student assistant, made the same 
attempt and succeeded in getting a few Crataegus aphids to establish 
imperfectly on apple. In view of the immunity of most Crataegus 
seedlings at the time (in late summer), when all of these tests were 
made, the results were not surprising. 
In 1917 Mr. William Lee, a student assistant working under the 
writer’s direction, repeated the tests and included in his experiments 
Crataegus seedlings which he had previously found to be congenial 
to Crataegus aphids. His results are given in Table IV. Aa-C17 to 
