22 THE HOP APHIS IN THE PACIFIC KEGION. 



severely injured that they were not worth picking, and they were left 

 in the field. (See PI'. IV, figs. 1, 2.) 



Where control work is attempted the infestation seldom becomes so 

 severe as to retard the growth of the vines, and it is the late injury — 

 the accumulation of honeydew upon the cones and the resulting 

 growth of the black fungus — which is most to be feared. 



HONEYDEW AND ITS EFFECT ON THE HOPS. 



Honeydew is a substance which is excreted from the anal opening 

 of the aphides. It is composed largely of gums and sugar and is 

 sticky and sweet to the taste. On warm afternoons it may be seen 

 falling as a mist from severely infested vines. 



Hops covered with honeydew are sticky, do not have the normal 

 amount of crispness, and when pressed between the fingers remain 

 flattened out. Honeydew may under some circumstances increase 

 the weight of the crop. One grower estimated that he made SI, 000 

 on honeydew in 1911. However, the quality of the crop was greatly 

 injured, and had the demand for hops been less the grower would not 

 have been able to sell, and his crop would have been a complete loss. 



Even though under certain uncontrollable circumstances the pres- 

 ence of honeydew may increase the income from a crop of hops, their 

 quality is injured, and the hone}^dew is the medium for the black-smut 

 fungus, which will, in ninety-nine cases out of one hundred, so injure 

 the quality of the crop that it will be unsalable. 



BLACKENING OF HOPS. 



Neither the honeydew nor the aphides are directly responsible for 

 the blackening of the hops. The blackening is due to a smut fungus 

 (Cladosporium sp.) commonly called "mold," which grows upon the 

 honeydew. If the honeydew happens to be upon the hop cones, this 

 fungus gives the hops a black, moldy appearance, which is extremely 

 undesirable. 



NATURAL ENEMIES. 



Several predaceous insects have been observed attacking the hop 

 aphis at Perkins and at Santa Rosa, Cal. The ladybirds Hippodamia 

 convergens Guer., Coccinella calif ornica'M&Tmh.., Coccinella aodominalis 

 Say, and Chilocorus orbus Cas. were frequently found among the 

 aphides. Some eggs of Hippodamia convergens deposited among the 

 hop aphides are shown in Plate V, figure 1. CJirysopa calif ornica 

 Coq. was always abundant in the hop fields, and the larvae were 

 very active in feeding upon the aphides. 



The larvae of syrphus flies (PI. V, fig. 2) were abundant in the 

 hopyards. Syrphus opinator O. S. and Syrphus americanus Wied. 

 were reared from the larvae which were collected from hop leaves. 



