PROCEEDINGS OF THIRTY-SIXTH FRUIT-GROWERS ' CONVENTION. 125 



substantial armor. On the other hand it is less virulent, seldom becom- 

 ing numerous enough to form a continuous crust. Also, it is less 

 poisonous to the host, not producing a colored stain or killing the 

 attacked parts. The injury appears to be confined to the stunting of 

 the growth, in the worst cases, and dead leaves may hang over winter 

 on infested trees. Without causing serious injury to the tree this insect 

 may bring about considerable financial loss through its habit of locating 

 on the fruit. The presence of the greedy scale on the fruit causes 

 rejection in some markets. 



To successfully combat scale with sprays it is necessary to use some 

 wash which will kill by contact with the surface of the insect's body. 

 Poisons taken internally are not effective because the habits of feeding 

 prevent the imbibing of such substances applied to the surface of the 

 bark as a spray. On the other hand contact with the bodies is rendered 

 difficult because of the armored protection, and strong penetrating 

 washes must be used. Sprays capable of killing scale are too caustic to 

 permit of use on foliage, and so must be applied while the trees are 

 dormant or before many leaves have developed. 



A list of scaleicides will include the lime-sulphur solution, rosin soap, 

 whale-oil soap, distillate oil, and mixtures of oil- emulsions with lye. 

 For general purposes the lime-sulphur solution should be chosen. 



To continue with the discussion of insect pests, the plant lice or 

 aphids still remain to be considered in the class which are not controlled 

 by stomach poisons. The aphids feed in the same way as the scales, 

 but differ in some other respects. They are larger, and not protected 

 by a scale or armored covering, but in the case of the woolly aphis a 

 wool-like substance acts in much the same way. The aphids can change 

 position at any time, but if not disturbed may not do so. Propagation 

 is by means of both eggs and living young, and the unrestricted rate 

 of increase is stupendous ; but aphids have many enemies including 

 insects and fungus diseases. Weather conditions also have a great 

 influence on them, and the combined effects of all may be so great as 

 to almost exterminate the plant lice. 



The woolly aphis is the most persistent species attacking the apple, 

 and, perhaps, the world over, causes as much damage as any of the 

 scales. This aphid infests both the tops and the roots, and under Cali- 

 fornia conditions one form is always present, that is, females which 

 give birth to living young. Contrary to the general impression, the top 

 infestations are practically independent of those occurring on the roots. 

 In soils of light or sandy texture the roots may not be attacked, but 

 frequently abundant development occurs on the tops. Wintering-over 

 above ground is easy, in this mild climate, and small ones are often 

 found under the protection of rough places in the bark. The woolly 

 aphis multiplies rapidly in the spring and soon infests many of the 

 twigs, forming compact colonies, which become conspicuous by the 

 development of the white woolly covering. The same increase occurs 

 on the roots, but the subterranean form usually has its greatest develop- 

 ment later in the season. The toxic substances injected into the tissues 

 of the tree produce disturbances in cell growth resulting in the develop- 

 ment of galls and warts. On the roots, these galls frequently interrupt 

 sap flow and bring about decay. The tops are also stunted in the same 

 manner. In addition to the poisoning, a large quantity of sap may be 



