38 
BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
of a brood and thus reducing its economic value. The maggot of the 
fly pupates commonly among fallen leaves or rubbish at the base of 
the tree, forming a light brown puparium (sometimes dark purplish- 
brown, in which case the specimen is parasitized), with a paler 
median longitudinal stripe. The adult fly is a large, shining black 
form, with three interrupted, pale-yellow, arcuate cross-bands 
(rarely wanting), and is 12 mm. long. Syrphid larvae may be found 
preying upon walnut plant lice from May to November, although 
they are quite scarce in the two extreme months. 
Ladybird Beetles (Family Coccinellid^). 
Ladybird beetles are the principal enemies of aphides affecting 
walnuts. The author has observed the following species feeding on 
these aphides: (1) Olla abdominalis Say; (2) Adalia melanopleura 
Le Conte; (3) Coccinella Juliana Mulsant; (4) Adalia liumeralis Say; 
(5) Hippodamia convergens Guerin; (6) Hippodamia ambigua Le 
Conte; (7) Coccinella calif omica Mannerheim; (8) Adalia bipunctata 
Linnaeus; (9) CMlocorus orbus Casey. Nos. 1 to 8 in both adult 
and larval stages feed on the plant lice on the leaves, while the adults 
of the CMlocorus occasionally attack the winter eggs on the limbs. 
Nos. 1 to 4 are the most persistent enemies of the aphides, the others 
only appearing spasmodically on the trees. The Hippodamia group 
of lady birds seems to prefer such intensely gregarious plant lice as 
the plum louse (Hyalopterus arundinis Fabricius) or the bean aphis 
(Aphis rumicis Linnaeus) and pay much less attention to the more 
sporadic varieties such as the aphides on walnuts. 
Table XII indicates the predatory activities of five larvae of Olla 
abdominalis (the ashy-gray ladybird.) 
Table XII. — Olla abdominalis: Predatory activities on walnut plant lice, San Jose, 
Cal, 1912. 
Num- 
Num- 
Num- 
Larva 
Date of 
Date of 
ber of 
"lice" 
Date of 
ber of 
"lice" 
Date of 
ber of 
"lice" 
Date of 
Total 
Date of 
adult 
No. 
hatching. 
molt 1 . 
eaten 
molt 2. 
eaten, 
molt 3. 
eaten, 
pupation . 
eaten. 
to molt 
molts 1 
molts 
1. 
and 2. 
2 to 3. 
1 
Aug. 27 
Aug. 30 
29 
Sept. 2 
36 
Sept. 5 
91 
Sept. 13 
477 
Sept. 22 
2 
31 
Sept. 5 
38 
9 
30 
12 
45 
19 
417 
25 
3 
31 
5 
24 
9 
33 
12 
50 
18 
237 
25 
4 
31 
5 
35 
9 
27 
12 
59 
18 
234 
25 
5 
31 
5 
39 
9 
31 
12 
53 
18 
320 
25 
In all, 1,685 "lice" were eaten in 90 days, or 18.7 "lice" per day 
per larva. The "lice" were of similar average size to those consumed 
by the lacewing larvse (Table X). It was noticed that before the 
first molt the ladybird larvae would eat only very small aphides. 
The following is a brief account of the stages of the ashy-gray lady- 
bird (Olla abdominalis) (PI. III). The egg: Yellow, later becoming 
