142 



is also associated ^vith it. The insects attracted by its secretions 

 include many flies of the families Muscidae, Anthomyiidae, Oscinidae, 

 and Sykphidae, and many bees, besides Pompilidae, Ichneumonidae, 

 Braconidae and numerous smaller forms of insect life. 



Monellia caryella cannot be distinguished from M. caryae except 

 under a lens. In California, the normal food-plants of this species are 

 Juglans californica (the Cahfornia black walnut) and hybrids derived 

 from this tree. 



Walnut aphids have many natural enemies, all predatory, which 

 reduce their numbers from June to September. Unfortunately, they 

 do not appear in sufficient numbers until the nuts have been injured ; 

 artificial measures are therefore necessary. Should they appear in 

 early spring they would quickly wipe out the few aphids then present 

 and their progeny would starve to death. The commonest spider 

 predaceous on walnut aphids is Theridium placens, Keyserling, but it 

 is of little importance. Both mature and immature individuals of 

 the small black Capsid, Camptobrochis brevis, Uhler, attack this pest, 

 but they only appear in numbers in August and disappear in Septem- 

 ber. An Agromyzid, Leticopis sp., in icis larval state preys upon the 

 lice from June to August, but is never abundant enough to be of im- 

 portance. The larvae of two Chrysopids, Chrysopa majuscula, Banks, 

 and C. californica, Coq., are of economic value in California in this 

 respect. The closely allied, but smaller Hemerobiid larvae are also 

 predaceous. Next to the CoccineUids, Syrphid larvae are of greatest 

 importance in control. The following Syrphids have been reared 

 from larvae collected while feeding : — Catabomba pyrastri, L. ; 

 Sphaerophoria ynelanosa, Wilhst. ; *S. sulphuripes, Thoms. ; Allo- 

 grapta obliqua, Say, and Eupeodes volucris, 0. S, Syrphus opinator, 

 0. S., and probably other members of this genus, prey on the aphids. 

 Catabomba pyrastri is the most abundant as well as the largest of these 

 flies. Its aphidophagous capacity is almost double that of any of 

 the other species enumerated. Its economic value is reduced by a 

 parasite, Bassus sp., which often destroys as much as two-thirds of a 

 brood. The following CoccineUids have been found feeding on these 

 aphids : — Olla abdominalis, Say ; Adalia melayiopileura, Lee. ; Cocci- 

 nella Juliana, Muls. ; Hippodamia convergens, Guerin ; H. ambigua, Lee. ; 

 Coccinella californica, Mann.; Adalia bipunctata, L. ; A. bipunctata 

 var. humeralis, Say ; and Chilocorus orbus, Casey. The adults 

 of the last-named occasionally attack the winter-eggs on the branches, 

 while all the others, both in the larval and adult stages, feed on the 

 aphids on the leaves. The first four are the most persistent enemies, 

 the others only appearing spasmodically. Winter-spraying directed 

 against the eggs is the easiest form of artificial control. Lime-sulphur 

 and crude-oil emulsion are effective, especially the former. The spray 

 should be directed all over the branches and twigs so as to cover every 

 part. For spring or summer spraying a " combination of 2 per cent, 

 distillate-oil emulsion and commercial tobacco extract No. 2 (1 ta 

 1,500) " will prove effective. This tobacco extract contains 40 per 

 cent, nicotine. The application must be made under a pressure of at 

 least 150 pounds and it must be directed on the nuts and underside 

 of the leaves. Details are given of the many experiments in winter 

 and summer spraying from which the above conclusions are drawn. 

 A bibliography of 22 works is given. 



