16 BULLETIN" 278, U. S. DEPARTMENT OF AGRICULTURE. 



Seven days were required to kill the 20 larvae by arsenate of lead 

 paste, and the two powder forms of arsenate of lead gave almost 

 identical results. Arsenate of calcium, commercial, was one day 

 slower in killing, and slightly more foliage was consumed where this 

 material was used. The two forms of arsenate of calcium, home- 

 made, killed in 6 and 7 days, comparing favorably with the arsenates 

 of lead both in the length of time required to kill and in the amount 

 of foliage consumed. Arsenate of zinc, homemade, killed in 6 days, 

 with 0.20 to 0.29 square inch of foliage consumed. Arsenite of zinc, 

 commercial, required 8 days to kill all the larvae and 0.79 to 0.84 

 square inch of foliage was consumed. Lead chromate used at 

 increased strengths was again slow in its killing effect, and more 

 foliage was consumed than in the case of the arsenates. Three larvae 

 in one lot and one larva in the other lot of unsprayed were dead at 

 the time the experiment was closed August 4. On the two checks 

 20.17 and 20.56 square inches of foliage were consumed, respectively. 



Experiment IX. 



COMPARISON OP THE KILLING EFFECT OF ARSENATE OF LEAD, ARSENATE OF CALCIUM, 

 ARSENATE OP ZINC, ARSENITE OP ZINC, AND LEAD CHROMATE ON LARV.E OP THE 

 TUSSOCK MOTH. 



Three forms of arsenate of lead, three forms of arsenate of calcium, 

 lead chromate (commercial), arsenate of zinc, and arsenite of zinc 

 were tested against larvae of the tussock moth (Hemerocampa leuco- 

 stigma S. and A.). The experiment was started June 26 and closed 

 July 6, when all the larvae were dead except in the unsprayed lots. 

 Table IX gives the results of this test. 



The three forms of arsenate of lead killed in 4 days, except in one 

 lot of the paste form which required 6 days to kill; the amount of 

 foliage consumed for all the forms varying from 0.01 to 0.08 square 

 inch. Arsenate of calcium, commercial, required on an average more 

 than twice as long to kill as required by arsenate of lead, and consid- 

 erably more foliage was consumed. The two forms of arsenate of 

 calcium, homemade, killed in slightly less time than was required 

 by the commercial form. Lead chromate, commercial, used at the 

 strength of 8 pounds to 50 gallons of water killed in 6 to 8 days, which 

 was a longer time than required by the ordinary strength of arsenate 

 of lead. Arsenate of zinc, homemade, and arsenite of zinc, commer- 

 cial, were slower in their killing effect on this insect than was arsenate 

 of lead. Three larvae were dead in each of two lots of the unsprayed 

 and four dead in the remaining lot, and 5.55 to 7.20 square inches of 

 foliage had been consumed at the time the experiment was closed. 



