38 



BULLETIN 100, TJ. S. DEPARTMENT OF AGEICULTUEE. 



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^e). 



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) CoccineUa Juliana Mulsant; (4) Adalia Jkumeralis Say; 

 (5) Hippodamia convergent Guerin; (6) Hippodamia ambigua Le 

 Conte; (7) Coccinella calif ornica 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 lad}' 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 ivalnat 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 

 "lice" 

 eaten. 



Date of 

 adult 



Xo. 



hatching. 



molt 1 . 



eaten 



molt 2. 



eaten, 



molt 3. 



eaten, 



pupation . 









to molt 





molts 1 





molts 





emer 









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 larvae (Table X). It was noticed that before the 

 first molt the ladybird larvae would eat only very small aphides. 



The f ollo\ving is a brief account of the stages of the ashy-gray lady- 

 bird {Olla abdominalis) (PL III). The egg: Yellow, later becoming 



