32 



that these larvae feed only upon dead insects, and that they never attack 

 those still alive. 



For the destruction of the Codling Moth our growers of deciduous 

 fruits depend almost altogether upon spraying the young fruit with 

 Paris green and water. The proportions vary from 1 pound of the 

 Paris green in 160 gallons of water to 1 pound in 200 gallons. My own 

 observations and experiments indicate that the former strength is lia- 

 ble to injure the leaves somewhat, so it will be advisable to use it not 

 stronger than at the rate of 1 pound to 200 gallons of water. 

 _ On the 12th of May, 1890, I had twenty-two pear trees sprayed with 

 Paris green and water at the rate of 1 pound in 160 gallons, and to 

 this was added 4 gallons of the resin wash, composed of: resin, 20 

 pounds; caustic soda, 6 pounds; fish oil, 3 pints, and water sufficient to 

 make 100 gallons. This was added for the purpose of causing the solu- 

 tion to spread more readily over the trees and fruit. These pear trees 

 were kindly placed at my disposal by Mr. O. H. Richardson, of Pasadena. 

 They averaged about 10 feet in height, and the tops measured about 4 

 feet in diameter. Twenty eight gallons of this solution were used on 

 these twenty-two trees. I examined them at intervals throughout the 

 summer; the fruit had not been in the least injured by the solution, 

 but a very few of the leaves had small brown spots burned in them, not 

 sufficient, however, to produce any material injury. When ripe, fully 

 five-sixths of the pears on these trees were free from the attacks of the 

 larvae of the Codling Moth, whereas on adjacent trees not treated 

 nearly all of the fruit had been attacked by these larvae. 



Throughout the entire summer season these sprayed trees remained 

 free from the attacks of the Pear-slug {Eriocampa cerasi Peck), although 

 I found leaves on some of these trees in which the eggs of this insect 

 had been deposited; and upon adjacent pear, apple, and quince trees 

 that had not been sprayed these slugs were quite numerous. It would 

 well repay our growers to spray their trees with the above-mentioned 

 solution as a protection against the attacks of these slugs and other 

 leaf-eating insects. 



It is the custom of some of the growers in the northern part of the 

 State to first dissolve the Paris green in ammonia before adding it to 

 the water, but it is very doubtful that this is any improvement. 

 Ammonia is known to be very injurious to vegetation whenever brought 

 in contact with it. I am informed by Dr. H. W. Wiley, the chemist of 

 this Department, that Paris green, which ordinarily consists of a mix- 

 ture composed of one molecule of the acetate of copper and three mole- 

 cules of the arsenite of copper, is changed to an entirely different 

 chemical compound when treated with ammonia, this compound then 

 consisting of the acetate and the arsenite of ammonia combined with 

 an ammoniate of copper — a mixture much more soluble in water than 

 Paris green is. It is evident that the more insoluble the Paris green 

 is rendered the less liability there will be of its injuring the foliage of 



