26 PROCEEDINGS OF THE THIED ENTOMOLOGICAL MEETING 



against the pest, they can be made to give good results by one thoroughly 

 conversant with the habits of the insect. 



Another difficulty arises in connection with the treatment of this 

 insect — a difficulty which is only apparent after close observation of the 

 habits of the insect. The efficacy of insecticidal treatment depends, 

 amongst other things, upon two factors — the killing power of the in- 

 secticide and the efficiency with which it can be applied. HelopeUis can 

 only be treated by means of contact insecticides, which must be applied 

 to the insect. This is in itself a difficulty except in the case of young 

 ■forms, as described above. But supposing this difficulty be overcome, 

 and that the adult tea mosquito be covered with a drop of the insecticide, 

 and a drop of such a size that it would take considerable time to evapo- 

 late. One might-, suppose that that would kill him, but it does not, 

 for the reason that he cleans it all off, just as a cat if covered with treacle 

 would clean itself. For this reason any insecticide which has not suffi- 

 cient penetrating power, even though properly applied to the insect, 

 does very little good, and since insecticides with a sufficient corrosive 

 power burn the young shoots spraying to kill the adults presents in- 

 superable difficulties. Spraying against the tea mosquito therefore boils 

 down to this, that until a substance is discovered which exerts a powerful 

 penetrating action on the insect and at the same time is harmless to the 

 young shoots, we must confine ourselves to applying spray fluids with a 

 high surf-ace tension at a time when the bulk of the insects are in the 

 young stages, and the spraying should consist of a thorough soaking of 

 the bush, to ensure that it will run down the branches and form drops 

 at all the nodes. Otherwise no beneficial results can be anticipated. 



We have another case — based on rather different lines. This is a 

 case too where an intimate knowledge of the behaviour of the insect 

 was necessary. The red spider of tea {Tetranychus bioculatus W. — M.) 

 in North-East India lives for the most part on the upper surface of the 

 leave's of the plant. Many sprays have been applied with the hope of 

 dealing with red spider without success. The reason for their non- 

 success was in many cases due to the fact that the red spider lives under 

 a web, which is very fine and almost invisible, but which is nevertheless 

 of considerable strength. It is very close to the leaf, but at the same 

 time the dimensions of the red spider are so small that nothing above 

 the net or web will touch it, and I found that after spraying for red 

 spider the insecticide rested in drops above this net while the insects 

 ran about happily underneath. In treating red spider it is 

 therefore necessary to break down this web, and we find that lime- 

 sulphur, which generally contains much suspended matter, will break 

 down this web, and in many cases differences in the action of different 



