December, '17] PETERSON: aphid egg susceptibility 559 



were sprayed with a 2 per cent solution of crude carbolic acid plus 

 enough laundry soap to break the surface tension of water and then 

 placed in a moist chamber. In an hour or more after treatment the 

 brittle outer layer was soft and wrinkled and could be easily removed. 

 The general decidedly glossy black appearance of all eggs treated with 

 crude carbolic acid in the various experiments and their manner of 

 shriveling also indicated a disintegration of the outer brittle layer. 



Furthermore many substances are splendid desiccating agents and 

 any material possessing this quality might be able to extract the water 

 content of the ovum or embryo and thus prevent further development. 

 Lime-sulphur, so far as observed, seems to have some desiccating 

 effect and possibly crude carbolic may likewise act in this way. 



Any toxic substance which will penetrate the egg coverings and 

 attack the living embryo would naturally be an important agent in 

 control and probably more direct in its eff set than the foregoing ways. 

 The extent of this penetration by various substances is difficult to 

 distinguish and as yet no technic has been found which might be used 

 in determining this point. 



Another possible means of control would be the discovery of some 

 chemical which will loosen the egg from the twig and cause it to fall to 

 the ground. There is some indication that sodium-hydroxide tends 

 to produce this result. 



The more important and common contact insecticides and various 

 chemicals have been tried on the eggs of all three species, in the green- 

 house with A. avence, out-of-doors at the laboratory with A. avencc, A. 

 pomi and A. sorhi, and in the orchard (hme-sulphur, nicotine sulphate 

 and "scalecide" only) with A. avence and A. sorhi. In all cases some 

 or all of the eggs are susceptible to any contact insecticide or other 

 chemical used in the various experiments. Of the three species, A. 

 avencc is apparently more susceptible than A. pomi or A. sorhi to the 

 various substances. 



The following table gives a brief summary of a large series of experi- 

 ments conducted with various insecticides and other chemicals. The 

 percentage of kill is figured on the basis of considering the number of 

 eggs hatched in the check as 100 per cent. If all the eggs were taken 

 into consideration each of the following percentages would be closer to 

 100 per cent; an 80 per cent kill would be 90 per cent or even greater 

 in the average experiment. 



Material Used Percentage Killed 



Lime-sulphur, 1-8 or 1-9 85%-100% 



Lime-sulphur, 1-8 plus "Black-leaf 40," 1-500 97% 



"Black-leaf 40," 1-500 plus laundry soap, 2 lb. to 50 gal. 45% 



Laundry Soap, "Fels Naphtha," 2 lb. to 50 gal 5%- 33% 



"Scalecide," 1-15 25%- 65% 



