TREATMENT FOR CONTROL OF APPLE APHIDS. 51 



pubescence over them in such a manner that the delicate insects were 

 apparently unable to force their way from the eggs. This fact — that 

 the action of lime-sulfur against the unhatched eggs appears to be mainly 

 mechanical — presents an element of great uncertainty concerning results 

 that would obtain under field conditions. For instance, the occurrence 

 of a rain between the time of application and the normal hatching time 

 for the eggs might alter results to a great extent, as many of the eggs 

 which are stuck down and potentially unable to hatch would probably 

 thus be liberated, so that hatching might result. This contingency 

 emphasizes the desirability of making the application of the lime-sulfur 

 at the late dormant period if success against the aphid eggs is aimed at, 

 in order to make the space of time between treatment and the normal 

 hatching period as brief as possible, and to eliminate anj^ unfavorable 

 meteorological factors that might lessen the efficiency. As will be shown 

 later the various elements that combine to make aphid control by lime- 

 sulfur treatment against the eggs during the dormant or late dormant 

 periods a matter of much uncertainty, as compared with other practices 

 discussed later, miUtate against its use at either of these periods, unless 

 no other treatment against the aphids is intended, in which case the late 

 dormant treatment should give the most satisfactory results. No such 

 mechanical action was evident in the case of the miscible oils, so that 

 whatever kilUng of the eggs may have resulted from the use of these 

 insecticides was undoubtedlj^ of a chemical nature. 



Comparative Tests for the Destruction of the Living Apple 

 Aphids. 



These tests were made against living apple aphids on twigs whose 

 foliage showed varying degrees of expansion from just after the splitting 

 open of the buds, the real delaj^ed dormant period, up to a development 

 of three-fourths of an inch or more, the latter being tested mainly to 

 determine the extent of foliage injury likely to result from the treatment. 

 Full dormant-season strength of lime-sulfur and miscible oils was used 

 and this same strength of lime-sulfur in combination with nicotine sul- 

 fate, observations being made both as to their killing power and their 

 effect upon the foliage. Careful counts were made of the number of 

 living plant lice present upon the twigs before and after the dipping 

 treatment, and from this the killing efficiency of each material could be 

 readily estimated. The results follow: — 



