56 Bulletin 332 



various cliecks corresponds with the percentage of hatch where the 

 laundry soap was used at the rate of 1 gm. to 200 cc. 



The results of the experiments with a 1 per cent solution of the 

 various acids are not very conclusive, and they are also somewhat 

 inconsistent. This is probably due to the fact that a 1 per cent 

 solution is not strong enough to produce an appreciable amount of 

 actual kill, especially when applied early in the season. A 2 per 

 cent solution probably would have given better results, at least the 

 experiments conductetl in 1917 indicate as nnu-h. Even though the 

 1 per cent solution did not produce a great amount of kill, neverthe- 

 less the smallest percentage oT li;itched eggs occurred when the spray 

 was applied in the latter part of ^March near the time when the 

 nymphs emerge. 



In order to determine the etfectiveness of the varying strengths 

 of crude carbolic acid, cresol U. S. P., and phenol C. P. with fish- 

 oil soap, a large number of experiments were conducted out-of-doors 

 at the laboratory throughout tiie month of March, 1918. The acids 

 were used in three different strengths 0.5, 1, and 1.5 per cent, and 

 the fish-oil soap solutions (made from solid soap) in two strengths: 

 1 gm. to 100 cc. (= 1 pound to 12 gallons) and 1 gm. to 50 cc. 

 (= 1 pound to 6 gallons). All possible combinations were made 

 l)etween the three strengths of each acid and the two strengths of 

 the fish-oil soap. Table ]5 shows in condensed form, similar to 

 foregoing tables, the treatment given, time of application, source of 

 the eggs, number of hatched eggs (h), total number of eggs and the 

 percentage of hatch. 



A general survey of the results of the experiments in table 15 

 again brings out the point that a contact insecticide applied late 

 in March just before the nymphs emerge will kill the greatest 

 number of eggs. In the four trials with each strength of acid on 

 March 1, 5, 14 and 23 the smallest percentage of hatch occurred 

 where the applications were made on March 14 and 23, and in most 

 cases when applied on March 23. These results indicate that the 

 acid can more readily penetrate to the embryo through the pig- 

 mented layer alone (after the outer shell splits) than through 

 both layers when the outer covering is whole. The greatest number 

 of eggs showed a split outer covering on March 23. 



A comparison of the effectiveness of the three acids at similar 

 strengths shows that crude carbolic acid killed the largest per- 

 centage and phenol the least while cresol U. S. P. was almost as 

 effective in some experiments as crude carbolic acid. A comparison 

 of all the experiments, where the acids composed 1.5 per cent of 

 the spray, brings out the rcs])ective effectiveness of the three acids. 

 Why the ciiide carbolic acid should be the most effective is nn- 



