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: 

 Catabomba pyrastri Linnaeus (1911-12); SpTiseropTioria melanosaWil- 

 listbn (Aug. 24, 1912); SpTiseropTioria sulpTiuripes Thomson (Oct. 15, 

 1911) ; Allograpta obliqua Say (Aug. 6, 1912) ; Eupeodes volucris Osten 

 Sacken (July, 1911). Syrplius opinator Osten Sacken, and probably 

 other members of this genus, prey on the aphides. Catabomba 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. 



1 Hatched on this date. 



2 Pupated on this date. 



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 



C 1 ) 

 4 

 15 

 20 

 12 

 11 

 11 

 23 

 68 



4 

 15 

 15 

 17 

 17 

 18 

 36 

 46 



Sept. 9 



53 

 65 

 76 

 17 

 70 

 62 

 84 

 74 

 71 



59 

 85 

 62 

 20 

 S3 

 77 

 63 

 83 

 105 



Sept. 18 



92 

 50 

 36 

 35 

 214 



107 



30 



10 



19 



104 



31 



11 



20 



10 



Sept. 2 



3 



12 



21 



2 13 



13 



22 





4 



14 



Total 





5 



15.. 



959 



1,035 



6 



16 





8 



17 











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 



