484 



JOURNAL OF ECOXO^IIC EXTOMOLOGY . 



[Vol. 8 



Observatioxs 



Notes taken during the course of the experiments show very clearly 

 and conclusive^ that the lead hydrogen arsenate is quicker acting than 

 the basic salt and that smaller amounts are required for killing effi- 

 cienc3^ Also, that although the caterpillars on the experiments sprayed 

 with the basic form lived longer, they finalh^ died, and with strengths 

 where less than 2 lbs. to 200 gallons was used the damage done before 

 they died was not serious. These experiments further show that the 

 killing efficiency is reduced in proportion to the reduction of the amount 

 of material used, and that beyond certain strengths they lose their 

 destructive value because the caterpillars cause ver}^ serious damage 

 before the quantity of poison eaten is large enough to kill. 



A comparison of the efficiency values shows that the lead hydrogen 

 arsenate in strengths of 2 to 50 was quicker acting than the basic, but 

 the results obtained with the latter were satisfactory in that practically 

 the same amount of foliage was eaten in both xBases. In strengths of 

 2 to 100 the difference in action was greatly in favor of the lead hydro- 

 gen arsenate but only a slight difference was noticed in the amount of 

 foliage destroyed. 



In strengths of 2 to 200 similar conditions were noticed, but with the 

 basic lead arsenate the amount of foliage destroyed was increased. 

 In strengths of 2 to 400 both materials acted more slowly and a con- 

 siderable part of the foliage was eaten on the basic lead arsenate exper- 

 iment. The lead hydrogen still remained satisfactory. 



In strengths of 2 to 800 practically the same conditions existed, the 

 poison acted slower and the amount of foliage eaten increased. 



In strengths of 2 to 1200 neither form prevented serious damage and 

 with the basic form the first twigs were completely defoliated and a 

 second set partly destroyed. As shown in the table these experiments 

 were discontinued before all the caterpillars died because it was not 

 thought necessary to carry them further. 



Further comparisons showed that the lead hydrogen arsenate 2 to 

 200 was more efficient than the basic 2 to 100 and that the lead hydro- 

 gen arsenate 2 to 400 was more efficient than the basic 2 to 200 in the 

 protection of foliage. 



In the tables it will be noted that as a rule only a few died the first 

 day or two, the heaviest drop occurring within two or three days. 

 This may be accounted for in several ways. 



