368 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 12 



tied together and then suspended in a perpendicular position on two 

 wires which ran across the upper portion of a large empty wooden 

 box. The large boxes were located out-of-doors in an open spot near 

 the laboratory, and thus the twigs were exposed to all weather con- 

 ditions, similar to that of the orchard. The above laboratory method 

 of spraying and caring for the eggs is somewhat ideal, yet the results 

 obtained for the past three seasons have been very satisfactory in 

 ascertaining the exact effect of each spray and their comparative values. 

 The results of this laboratory method have exactly duplicated the 

 results obtained in the orchard where lime-sulfur 1-9, lime-sulfur 1-9 

 plus nicotine 1-500 and "Scalecide" 1-15 have been used. During 

 1918-1919 the above out-of-door laboratory method for determining 

 the value of various sprays in killing the eggs has been relied upon almost 

 entirely. In several orchards a few observations were made on the 

 effect of lime-sulfur, 1-9 plus nicotine, 1-500 and the results corre- 

 sponded with results of similar experiments at the laboratory. 



Contact Sprays 



Previous morphological and ecological studies on the eggs of plant 

 lice found on apple trees show conclusively that they may be killed 

 by various contact sprays. It has been shown that the eggs are most 

 susceptible to environmental factors and various chemicals just pre- 

 vious to the hatching period. The period of susceptibility commences 

 about the first week in March with A. avence and probably a week or 

 ten days later with A. pomi. At this time the eggs are commencing 

 to rapidly split their outer coats. The maximum susceptibility of 

 the majority of the eggs probably occurs just at the time the eggs are 

 starting to hatch in large numbers because at this stage the largest 

 percentage have split their outer shells preparatory to severing the 

 inner black membrane. This season's results indicate that the sus- 

 ceptibility of the eggs of A. avence and A. pomi to various sprays are 

 approximately the same while observations made in 1917 indicate that 

 the eggs of A. sorhi and A. pomi are somewhat more resistant to various 

 sprays than eggs of A. avence. Undoubtedly the different sprays act 

 on the eggs in various ways. Some may act as desiccators (probably 

 lime-sulfur and others) which harden the outer shell more or less or 

 extract the water content from the embryo (especially if applied after 

 the outer layer has split). Other substances soften and disintegrate 

 the outer highly impervious layer (crude carbolic acid), thus exposing 

 the inner layer to evaporating factors. The physical reaction of con- 

 tact insecticides may be important, but it is probable that the toxic 

 effect of various insecticides upon the embryo is much more important. 

 This is a point that is diffcult to determine. 



