Studies on Eggs of Apple Plant Lice 23 



have some knowledge of the chemical nature of the layers about 

 the egg. A few qualitative tests have been conducted with this 

 point in view, but as yet nothing definite has been determined. 

 From a physical standpoint the effect of certain substances has 

 been observed and these will be discussed briefly. 



In order to control the aphid in the egg stage the material used 

 must prevent the nymph from hatching or it may be of such a 

 nature as to kill the nymph as it hatches. The preventive may act 

 in several ways. Any substance which will harden the outer semi- 

 transparent shell and thus makes it impossible for the nymph to 

 emerge would be satisfactory, or the material used could have the 

 opposite effect, that is, soften or dissolve the outer layer and thus 

 expose the inner, pigmented layer to evaporating factors such as 

 wind, heat or low humidity. Furthermore, many substances are 

 splendid dessicating 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. Again, the use of any 

 toxic substance which will penetrate the egg coverings and attack 

 the living embryo would naturally be a control measure. Another 

 possible means of control Avould be the discovery of some chemical 

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

 ground. 



Dormant lime-sulfur apparently hardens the outer covering, 

 at least it was noted that a number of treated eggs did not com- 

 pletely collapse and in many eases the outer layer retained its 

 normal shape while the black pigmented layer and the contents of 

 the embryo within were completely shriveled. Such eggs are easily 

 recognized in that they are lighter in color because of the air space 

 within. Besides this hardening effect, lime-sulfur seems to act as a 

 dessicating agent and it may also actually penetrate all the layers 

 and serve as a toxic substance on the embryo. 



So far as could be seen with a microscope, no decided visible 

 effect was evident in eggs treated with other common contact in- 

 secticides such as nicotine, soap solutions and miscible oils. In some 

 cases where eggs were treated with miscible oil, particularly oils 

 which possess some crude carbolic derivatives, they appeared to be 

 more glossy. So far as is known, the above substances probably 

 act as toxic agents which kill by penetrating the layers of the egg 

 and attacking the embryo. 



. A weak solution of crude carbolic acid will soften and ap- 

 parently disintegrate the outer shell of the aphid egg. In several 

 experiments the eggs of A. aveim and A. pomi were sprayed with a 

 1 per cent and a 2 per cent solution of crude carbolic acid, and with 

 varying strengths of cresol (U. S. P.) plus enough laundry soap 

 to break the surface tension. In a few minutes after treatment 



