36 BULLETIN 100, U. S. DEPARTMENT OP AGRICULTURE. 



Spiders. 



The commonest spider predaceous on walnut plant lice is The- 

 ridium placens Keyserling. This spider may be found on the trees 

 during the months of August and September and has a habit 

 of curling around itself the edge of the leaf under the protec- 

 tion of which to deposit its egg sac. This species was determined 

 by Mr. Nathan Banks, of the Bureau of Entomology, who says of it 

 "* * * a gpecies found on the Pacific coast. They do not 

 choose their food, but from location of web are apt to get many 

 plant lice." This and other spiders are of comparatively small 

 economic importance in the control of aphides. 



Camptobrochis brevis Uhler. 



Camptobrochis brevis Uhler, which was determined by Mr. Otto 

 Heidemann, of the Bureau of Entomology, is a small black capsid, 

 measuring in the adult stage 4.2 by 1.9 mm. Its larva is white, with 

 conspicuous black markings. Both immature and mature individ- 

 uals were observed actively and abundantly attacking plant lice 

 during August, 1912. They do not occur in numbers earlier in the 

 year and disappear in September. Thus their beneficial work is 



limited. 



Leucopis sp. 



A fly of the family Agromyzidae, Leucopis sp., in its larval state 

 preys upon walnut plant lice from June to August. The small 

 yellow maggots superficially resemble syrphid larvae. They are 

 never very abundant and are not a great factor in the control of the 

 "lice." The life cycle in summer is completed in 24 days or less 

 and there are several broods in California. 



Chrysoped or Lacewing Flies. 



Of scarcely less importance economically than the ladybird beetles 

 and sjrphid maggots are the active reddish-brown larvae of the "lace- 

 wings." GfirysoxxL majescula Banks and C. calif ornica Coq. are two 

 species of economic importance in California. Table X shows the 

 predatory activities of two larvse of the latter species hi the fall of 

 1912. The aphides consumed by these larvae were of all sizes and 

 averaged about 1.5 by 0.5 mm. 



Table X. — Chrysopa calif ornica: Predatory activities on walnut plant lice, Walnut 



Creek, Cal., 1912. 



Larva 

 No. 



Date of— 



Number 

 "lice" 



eaten to 

 moltl. 



Date of 

 molt 2. 



Number 

 "lice" 

 eaten, 



molt 1 to 

 molt 2. 



Date of 

 spinning 

 cocoon. 



Number 

 "lice" 

 eaten 

 from 

 molt 2 

 to pupa- 

 tion. 



Total 

 "lice" 

 eaten. 



Num- 

 ber 

 days 

 feed- 

 ing. 



Hatch- 

 ing. 



Molt 1. 



1 

 2 



Sept. 18 

 18 



Sept. 22 

 21 



11 

 22 



Sept. 27 

 20 



70 

 57 



Oct. 8 



265 

 300 



346 

 379 



20 

 19 



