242 INJURIOUS AND USEFUL INSECTS 



surfaces not easily commanded by the eye, and also to illu- 

 minate dark recesses by reflected sunlight. Special knives, 

 with the end of the blade bent at an angle, were much used 

 to scrape off the clusters. Of late years spraying with crude 

 petroleum (unignited) has been found an effectual means of 

 destroying the egg-clusters in stone walls. 



2. Destruction of the larvae. — Several different methods 

 were adopted : — 



(A.) Banding. — Large trees, which are difficult to search, 

 were often kept free of the caterpillars by bands smeared with 

 a mixture of tar, printers' ink, and petroleum. The bark is 

 smoothed, enclosed by cotton waste, and this by a narrower strip 

 of tarred paper, the whole being then tied round with cord. The 

 bands should be applied shortly before the emergence of the 

 larvae, and repainted twice a week. They should be fixed at 

 such a height that they are not liable to be rubbed by cattle. 

 In Germany Raupenleim, a kind of crude vaseline, is much 

 used for smearing the bands. 



(B.) Spraying. — Paris green (aceto-arsenite of copper), finely 

 powdered, was mixed with water, in the proportion of from 

 I to 4 lbs. to 150 gallons. The weak mixture did not injure 

 foliage, but was too weak to kill many caterpillars ; the strong 

 mixture injured foliage greatly, and could not be counted upon 

 to kill older larvae. It was not expected that the larvae would 

 be killed by the direct application of the arsenical solution, but 

 by feeding on the poisoned leaves. On the whole this method 

 was pronounced "ineffective and unsatisfactory." London 

 purple (arsenite of lime) had about as much effect as Paris 

 green upon the caterpillars but injured the foliage more. 

 Arsenate of lead, mixed with water in the proportion of one 

 to five or six, was a new insecticide brought into use by the 

 Massachusetts Board. It has proved more effective than any 

 other arsenical compound, adhering better to the leaves, which 

 it does not seriously injure. All these insoluble substances 

 are difficult to apply. The mixture must be continually stirred, 

 and the nozzles of the pumps often get choked. Petroleum 

 emulsions and various soap-washes were found advantageous 

 only where the larvae were dense. In general, spraying with 

 poisonous fluids is most successful, and least injurious to 

 foliage if practised early in the season. Trees in blossom 

 should never be sprayed. The blossoms are injured, the 



