PETROLEUM-SOAP EMULSIONS. 305 



more resistant. According to Marlatt and Slingerland, 33 per cent 

 emulsions do not act on the eggs, besides they resist pure petroleum, 

 benzene, spirits of turpentine, carbolic acid, and liquid soda. Winter 

 treatment with 25 per cent emulsions destroys the hibernating adults. 

 Spring treatment with 2 per cent emulsion, at the time of the hatching 

 of the larviB, destroys 90 per cent (Slingerland). Fischer recommends 

 the extract of quassia emulsion. 



Psylla mail, Forst (the apple chermes). — Winter treatment is 

 without effect, for it is not the adults that hibernate but the eggs. It 

 is better, therefore, to treat the larvae in the springtime, some days 

 after hatching, to obtain appreciable success. The more frequent 

 victims of petroleum are the Aphides (lice), for the insects of that 

 family are the most delicate. They are easily destroyed by emulsions 

 when they are not sheltered in a fold of the leaf in galls (Tetraneura) 

 or in cankers (Schizoneura) inaccessible to sprays. It is well, there- 

 fore, to proceed with the treatment before the louse has assumed a 

 great extension, at .the moment when it is discovered. In these con- 

 ditions the destruction succeeds, and even the Delacroix 1 per cent 

 emulsion. Nevertheless, Muhlberg Barnard, Fleischer, Koebele, and 

 Alvood recommend a 3-4 per cent emulsion against the living lice 

 in the open, as those of the rose. When the lice are protected under 

 a curled leaf, as in the case of the apple, peach, and gooseberry, 

 the treatment does not succeed; 6-6 per cent emulsion only killed 25 

 per cent of the gooseberry aphis. Ki'uger's emulsion, consisting of 

 equal parts of soft soap, petroleum, and water, is most used in Germany 

 and diluted so as to make a 1-6 per cent emulsion ; in France it is- 

 Delacroix's containing 2 per cent of soft soap,*l per cent of petroleum, 

 and 1 per cent of carbonate of soda. The winter treatment of trees 

 with concentrated emulsions, containing 25-30 per cent of petroleum, 

 cannot act except on species which hibernate in the state of apterous 

 females, for these emulsions are, according to Goff, incapable of killing 

 the winter eggs. 



Schizoneura lanigera, H. (woolly aphis). — The woolly aphis forms 

 big cankers on the bi-anches on which the colonies vegetate indefinitely. 

 These lice form hiding-places there, where it is almost impossible to 

 reach them, and as they are, moreover, covered with a sort of down, 

 aqueous insecticides have no action on them, for they neither reach 

 nor penetrate them. The moment must be chosen when the winter 

 egg is hatched, for at birth the insects have no down, are delicate and 

 frail. Concentrated emulsions containing as much as 66 per cent 

 petroleum can then be used on the cankers, preferably after excising 

 the ligneous portion. Success is absolute, yet Delacroix and Fischer 

 remark that an ordinary 3 '5 per cent emulsion, and even with 1 per 

 cent of petroleum and 1 per cent of carbonate of soda, acts on all the 

 lice it touches. Failures only occur with too thick colonies that cannot 

 be penetrated by the insecticide. In Sw^itzerland, petroleum and salt 

 water emulsions are used with success. According to Stedman 

 (Missouri Experimental Station), the ravages of the woolly aphis also 

 affect the underground portion of the apple-tree. He succeeded in 

 disinfecting the young trees without injuring their health, by uplifting 



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