INSECTICIDES. 



473 



pillars, of the fifth molt, were placed on willow branches 

 which had been sprayed with arsenate of lead, in the propor- 

 tion of 10 lbs. to 150 gal. of water. Two died the second 

 day ; three pupated the fourth day ; two died the fifth and 

 one the sixth day ; one pupated the thirteenth and one the 

 fifteenth day. 



No. 141 (field experiment) . — June 21, 1893. A branch 

 of a small oak tree was sprayed with arsenate of lead, in the 

 proportion of 10 lbs. to 150 gal. of water, and eight fifth- 

 molt caterpillars placed upon it. August 19, all were dead. 



25 lbs. Arsenate of Lead to 150 gal. Water. 



No. 142. — July 1, 1893. A small branch of oak was 

 sprayed with arsenate of lead, in the proportion of 25 lbs. 

 to 150 gal. of water, and ten large fifth-molt caterpillars 

 placed upon it. All died within one week. Foliage unin- 

 jured. 



Even larger proportions of this poison than the above 

 were occasionally used in spraying operations in the field, 

 with fairly satisfactory results. 



Comparative Effects of Paris Green, Paris Green and Lime 

 and Arsenate of Lead. 

 A careful study of the comparative effect of equal weights 

 of the three substances used in the preceding experiments 

 shows that there is practically no choice between Paris green 

 and Paris green and lime, so far as the destruction of the cater- 

 pillars is concerned. The largest amount of these poisons 

 which can be used without injuring the foliage is about 1 lb. 

 to 150 gal. of water, and at this, or even a much larger rate, 

 the percentage of caterpillars destroyed is not satisfactory. 

 Since arsenate of lead in almost any strength is not injurious 

 to foliage, a much larger amount can be used than of any of 

 the more soluble arsenical compounds ; thus the superiority 

 of this poison as an insecticide is at once evident. While 

 arsenate of lead may be considered the best insecticide for 

 destroying the gypsy moth In the caterpillar stage, even this 

 poison is of small value in exterminating this insect, since 

 many of the caterpillars survive after feeding upon leaves 

 sprayed with large proportions of this poison. 



