The Tea insects of India. 59 



dissolved in water and sprayed in this form over the afPected plants. 

 Cakes of soap and sulphur mixed ready to be dissolved in water are said 

 to be already an article of manufacture in England (sec foot-note to 

 page 54-), This substance can therefore be easily procured and would 

 seem to be well worth trying upon an extensive scale, before rnncluding 

 definitely that the system at present adopted is incapable of further 

 improvement. 



Sulphur is one form or another at present to be the most promising 

 agent for use against mites generally, From the experiments^, however, 

 which have been made elsewhere, it is almost certain to have little effect 

 on pests which belong to the zoological group Insecta. Tn other words, 

 while mites are exceedingly susceptible to sulphur, insects (properly so 

 called) are but little affected by it. 



It must be borne in mind that in order to give satisfactory results, 

 not only must an insecticide be carefully prepared and applied in the 

 right proportions and in the proper manner, but it is necessary to ascer- 

 tain that the nature of the insect, which it is required to destroy, is 

 such as to render it amenable to the particular form of insect poison 

 employed. The necessary caution also must be exercised in cases where 

 the application is hurtful to the higher animals and man. 



From the contradictory statements which have been made by those 

 who have experimented in India with identical insecticides, it appears 

 that a good deal of misunderstanding exists with regard to the nature 

 of these substances. In particular the fact seems to be often over- 

 looked that because an insecticide is either effective or the reverse when 

 applied in a particular manner against one insect, it by no means neces^i 

 sarily follows that it will have the same effect when used, either in the 

 same or in some other manner, against a different species. 



With this preface we may proceed to consider a few of the more 

 important insecticides and mechanical appliances invented in America 

 for the destruction of insects. It will be unnecessary to repeat what 

 has already been said either about the sulphur treatment which has been 

 fully dealt with above, or concerning such methods as that of applying 

 bisulphide of carbon to root-feeding forms which has been sufficiently 

 described on page 6 under the heading Melolonthini. 



The subject may most conveniently be considered under the follow- 

 ing five headings : — 



(1) Kerosine Emulsion. 



(2) Pyrethrum. 



(3) Arsenical Washes. 



(4) Hydrocyanic Gas. 



(5) Hopperdozers. 



