August, '21] STEARNS: ORIENTAL PEACH MOTH 339 



During the simmier of 1920, these tests were cantinued, and on a 

 sufficiently larger scale to give results that would eliminate the chance 

 element present in tests in which only small numbers of eggs are em- 

 ployed. In this study, twenty-six experiments, comprising thirty- 

 eight tests with eighteen insecticides and involving 9894 selected eggs 

 were conducted at the Leesburg Field Laboratory. The results sub- 

 stantiate those obtained in the earlier tests. In addition, interesting 

 data were secured on the relative toxicity of different strengths of nico- 

 tine sulphate, when used alone, and also, when used in combination 

 with certain spreaders (caseinate and sea moss) and with an arsenical 

 (powdered lead arsenate). 



The method of procedure in these tests was similar to that described 

 in the previous report, The eggs deposited on the foliage of one-year- 

 old peach trees were always examined carefully with a hand lens, so 

 that only well-rounded and apparently viable ones entered into the 

 experiments. In applications, the atomizer was held at a sufficient 

 distance to prevent any drenching of the leaves; only a spray mist hit 

 them. Following apphcations, eggs were given daily binocular exam- 

 inations up to hatching, and then, the young larvae were continued 

 imder observation for 36 hours. 



Three series of tests were conducted, in all of which nicotine sulphate 

 (40 per cent) was employed at the varying dilutions 1-1600, 1-800' 

 and 1-500. In the first series, it was used alone; in the second series, 

 a spreader was added; and in the third series, both an arsenical and a 

 spreader were combined with it. Of the 9894 selected eggs, 4585 were 

 sprayed, and 5309 were reserved as a check. Although an endeavor was 

 made to distribute the eggs uniformly, a greater number were em- 

 ployed in those tests, in which applications were made at the more 

 common 1-800 dilution of nicotine sulphate. 



The efficiency, or killing power, of an insecticide is computed here, 

 by deducting the per cent of check eggs not hatching from the percent 

 of sprayed eggs not hatching, and in arsenical combinations, larvae 

 dead 36 hours after hatching. 



In the first series of tests, in which nicotine sulphate was used alone, 

 8.7, 70.3 and 80.5 per cent of the sprayed eggs did not hatch. At no 

 time did more than 10 per cent of the check eggs fail to hatch. The ac- 

 tual percentages of efficiency for the varying dilutions 1-1600, 1-800 

 and 1-500 were 3.8, 60.4 and 73.5, respectively. The greater dilution gave 

 practically no control, while the 1-800 dilution gave a little less than 

 two-thirds, and the 1-500 dilution an approximately three-fourths 

 control. 



