October, '15] 



MELANDER: SAN JOSE SCALE 



477 



At intervals of two or three weeks, sample branches were pruned 

 from each test and the condition of the sprayed scales was noted by 

 dissection under the prism binocular microscope. The numbers of 

 living and dead scales were recorded by means of a pair of tally reg- 

 isters operated by the examiner's feet. Here, naturally, enters the 

 personal element in forming a decision in the case of dying or just 

 dead scales. Practically all the counts were made by A. L. Melander 

 and M. A. Yothers checking against each other from different samples 

 of each test, and in the following tabulations the percentages given 

 are the average of their two counts. Not only is it extremely difficult, 

 if not impossible, to decide just when a scale insect dies, but the last 

 counts were further vitiated by certain scales dropping from the 

 branches. This seemed to be particularly true where the stronger 

 sulphur sprays were used, and forms a factor that should not be 

 neglected when discussing the insecticidal properties of these sprays. 

 It seems that a polysulphide spray changes the waxy covering so as to 

 render it difficult for the awakening scale to attach its spring secre- 

 tions. Thus in some instances the body of the insect grows beyond 

 the scale-covering, loosening and raising it from the plant epidermis 

 so that ultimately it falls off. Such unprotected individuals perish 

 and drop from the branches. While this mode of death is more or 

 less of a factor in sulphur-lime treatment, yet it is not of great impor- 

 tance unless the spray is used unduly strong. 



Sulphur-lime is supposed to kill principally by chemical suffocation, 

 due to its strong affinity for oxygen. During the reaction the pro- 

 toplasm of the insect changes in appearance, becoming viscous and in 

 color luteous yellow until further change darkens the protoplasm to a 

 brown and changes its consistency to an oily meal. Just when the 

 transition point occurs where this reaction ceases to be reversible and 

 death ensues is unknown, but in interpreting results the insect at the 

 viscous, luteous stage is considered dead. During warm weather the 

 moisture of the protoplasm quickly disappears as soon as the insect 

 dies, and hence when scales die from the first shock of deoxygenation, 

 their dead condition can be interpreted within a few days or weeks. 

 Furthermore, in making these counts, only the small blackish over- 

 wintering scale insects are considered, since overwintering adults are 

 of extremely rare occurrence. After the males had emerged, their 

 empty shells were rated as living insects in order not to disturb the 

 balance of the sexes at the last count. Whatever element of uncer- 

 tainty might appear in making determinations of doubtful cases is 

 largely offset by the large numbers counted, for during the season 

 over 170,000 scales were individually dissected from the branches and 

 their condition recorded. 



