SOLUBILITY OF THE .SCALE OF LEPIDOSArHES ULMI, LINN. 269 



The Spiracles of the Insect. 



It is a generally accepted view that contact insecticides kill insects bv acting 

 detrimentally on the respiratory system. It will be sufficient for the purposes of 

 this paper to indicate the position of spiracles of this insect, because they are the 

 orifices through which the insecticides must act. There are two pairs of spiracles on 

 the ventral side of the insect. In the larva the first pair is situated on the prothorax 

 just behind and outward from the bases of the anterior legs, the second pair between 

 the meso and metathorax behind and outward from the bases of the middle legs. 

 The position of the spiracles of the adult female is shown in the accompanying 

 drawing ; in this stage the insect loses its antennae, legs, etc. The spiracles being 

 on the ventral side they are more or less protected by the body of the insect, and 

 this fact lessens the chances of the spraying fluid reaching them. 



Treatment. 



I am inclined to suggest the following method of dealing with this pest. The insect 

 confines itself mainly to the trunk, though it may spread a little way up the larger 

 branches. Taking advantage of this fact, scrubbing the trunk and the bases of the 

 larger branches with a hard brush and hot water is an excellent remedy. This should 

 be done in winter when the eggs are dormant. Too nnich emphasis cannot be laid 

 on the necessity for thoroughness in this operation. lathe following May and June 

 a close watch ought to be kept to find out when the insects are hatching out, because, 

 however thorough the scrubbing may be, some eggs are sure to be left untouched. 

 In order to kill these a weak solution of paraffin emvdsion is quite suitable. They 

 ought to be killed before they settle down. As the insects keep hatching out for 

 more than a couple of weeks, several spraying operations are necessary, only those 

 trees being sprayed which have insects on them. This involves a certain amount of 

 observation on the part of the person in charge of the orchard. I have not touched 

 on the subject of checks by natural enemies in this paper, because, I understand, 

 the ((uestion forms the subject of investigation by someone else. 



Conclusions. 



1. The scale is most probably not a wax. 



2. The ingredients of the spraying fluids in use have no solvent action on the scale. 



3. Any good residt obtained with these fluids depends on the physical property of 

 the paraffin oil contained in them. 



4. Scrubbing the trunks with a hard brush and hot water in winter, and then 

 spraying with weak kerosene emulsion in the following spring oidy those trees which 

 show newly hatched insects on them, are better methods of checking the spread of 

 the pest. 



I take this opportunity of thanking Prof. H. M. Lefroy, of the Imperial College of 

 Science, for suggesting to me this subject. My thanks are also due to Prof. Schrj^er 

 for assistance in the Bio-Chemical Laboratory of the College. 



