April. '21] 



parrott: dusts for sucking insects 



209 



were thoroughly dusted with preparations containing 0.5, 1.0 and 2.0 

 percent, nicotine. As previous experiments had indicated that there 

 was ver\' Httle difference between the three species wdth regard to their 

 susceptibihty to the dust, and since the majority of the nymphs belonged 

 to avencE, the counts were made without any attempt to distinguish 

 the different species. The eft'ects of the dusting on the aphids are given 

 in Table III. 



Table III — Results of Dusting Against Apple Aphids 



Treatment 



Dust 0.5 percent, riictire.. 

 Dust 0.5 peicent. nirotine. . 



Check 



Check 



Dust, 1 percent, nicotine. 

 Dust. 2 percent, nicotine.. 



Check 



Dust, sir-slacked lime 



lime-sulfur ard nicotine... 

 ChecV 



Average No. 

 Aphids per Bud 



3.02 



2.5 



2.56 



2.2 



2.4 



2.14 



2.3 



2.4 



2.03 



1.78 



Percent, dead 

 after 4 Days 



91.7 



98.7 

 27.1 

 65.5 

 87.6 

 97.2 

 47.8 

 78.6 

 97.5 

 60.0 



At the time of the opening of the apple buds the extent of infestation 

 by aphids may be greath^ influenced by such factors as driving rains, 

 sleet storms, high winds and low temperatures. The reduction in the 

 num.ber of insects on the checks by natural m_eans was considerable 

 in seme instances, and it is reasonable to suppose that similar influences 

 operated on the sprayed and dusted series. A study of the data shows 

 that, on the whole, dusting compared quite favorably with spraying in 

 insectic'dal efficiency. It should also be noted that a heavy application 

 of air-slaked lime resulted in a loss of 78.6 percent, of the aphids. 



One of the interesting results of the season's activities with aphids is 

 that different species are apparently not equally susceptible to dust 

 mixtures with the sam.e nicotine content. The fact that seme aphids 

 are more resistant than others was most clearly demonstrated in some 

 tests wnth M. solanifolii and 5. lanigera, which proved very much less 

 susceptible to treatment than the commion apple species, such as pomi, 

 avencB or sorbi. 



The Apple arid Grape Leajhoppers 



In the experiments against the apple redbugs, to which attention has 

 previously been called, the nymphs of Empcasca unicolcr and Empca 

 roiCB proved very susceptible to dust mixtures containing 0.5 and 1.0 

 percent, nicotine and fell completely paralyzed in large numbers on the 

 collecting sheets. As the control of these species was not contem^plated 

 when the work was undertaken, no attempt was made to determine the 

 effectiveness of the treatment in protecting apple trees. 



In an experiment with grapes, an application of dehydrated copper 

 sulfate and lime containing 2.0 percent, nicotine destroyed eighty 

 percent, of the nymphs of the leaf hopper. 



