WALNUT APHIDES IN CALIFORNIA. 
37 
Larva No. 1 ate on the average 17.3 "lice" per day, while larva 
No. 2 consumed 19.9 "lice" per day. The lacewing larvae appear 
in numbers toward the end of June and may be found until the end 
of October. There are probably at least three broods, the last one 
wintering in the cocoon, which is white, short oval, with a central 
brown annulation, and is spun among the leaves or under a piece of 
bark. The closely allied but smaller hemerobiid larvae also attack 
walnut plant lice. 
Syrphid Larvae. 
Next to the ladybird beetles the larvae of flies of the family 
Syrphidae are of greatest importance in the natural control of walnut 
aphides. The author has reared the following species of Syrphidae 
from larvae collected while they were feeding on walnut aphides: 
Catdborriba pyrastri Linnaeus (1911-12); SpJiseropJioria melanosa Wil- 
lis ton (Aug. 24, 1912); SpJiseropJioria sulpJiuripes Thomson (Oct. 15, 
1911) ; Allograpta obliqua Say (Aug. 6, 1912) ; Eupeodes volucris Osten 
Sac ken (July, 1911). SyrpJius opinator Osten Sacken, and probably 
other members of this genus, prey on the aphides. Catdborriba pyrastri 
is the most abundant as well as the largest of these flies. Its aphido- 
phagous capacity is almost double that of any of the other species 
enumerated above. Table XI indicates the predatory activities of 
two larvae of the last brood of this fly. 
Table XI. — Catabomba pyrastri: Predatory activities on walnut plant lice, Santa Jose, 
Cal.,1912. 
Date. 
Number of 
"lice" eaten 
by- 
Date. 
Number of 
"lice" eaten 
by- 
Date. 
Number of 
"lice" eaten 
by- 
Larva 
No. 1. 
Larva 
No. 2. 
Larva 
No. 1. 
Larva 
No. 2. 
Larva 
No. 1. 
Larva 
No. 2. 
Aug. 29.. 
0) 
4 
15 
20 
12 
11 
11 
23 
68 
0) 
4 
15 
15 
17 
17 
18 
36 
46 
Sept. 9 
53 
65 
76 
17 
70 
62 
84 
74 
71 
59 
85 
62 
20 
83 
77 
63 
83 
105 
Sept. 18.. 
92 
50 
36 
35 
2 14 
107 
30 
10 
19 
104 
31 
11 
20 
10 
Sept. 2 
12 
21 
2 13 
3 
13 
22 
4 
14 
Total 
5 
15 
959 
1,035 
6 
16 
8 
17 
Hatched on this date. 
Pupated on this date. 
The "lice" consumed were of a similar average size to those eaten 
by the chrysopid larvae (Table X) . The larva of Catabomba pyrastri 
is pale green, with three longitudinal white stripes the whole length of 
the body, and when fully extended exceeds half an inch in length. 
The anterior segments of the body are retractile, giving it a sluglike 
appearance. If food is plentiful the larva moves but little, although it 
is capable of rapid crawling over the foliage if food is scarce. A para- 
site, Bassus sp., preys upon it, often destroying as much as two-thirds 
