394 



[Nov. 1906. 



PLANT SANITATION. 



Entomological Notes. 



By E. Ernest Green, Government Entomologist. 

 ' Shot-hole-borer ' (Xyleborus fornicatus) remains a serious matter of con- 

 sideration with tea planters,— more particularly within a radius of ten miles around 

 Kaudy. The question is being complicated by the occurrence of wound-fungi 

 invading the galleries of the borer, and the attacks of white ants (termites) upon 

 the fungus-infested tissues. I have reports from certain estates that, owing to 

 the combination of these three evils the bushes are steadily deteriorating, and there 

 is a general cry for a radical cure. I may say, at once, that I can offer little hope 

 of such a cure. Though nothing must be left untried, (and I have a further series 

 of experiments in hand), I am not sanguine of finding any external application 

 that will exterminate the borer and be at the same time practicable (from the point 

 of cost) and harmless to the tree. It would be possible to coat the stems and 

 branches with some viscid material that would prevent both the egress of the 

 beetles then inside and the ingress of fresh insects from outside. I have already 

 tried two such materials,— coal-tar and ' smearoleum.' The former completely 

 killed the parts to which it was applied, while the latter effectually checked the 

 development of any new shoots upon the treated surface. Such treatment fails 

 also on the point of cost. Viscid mixtures cannot be applied by spray but must 

 be painted on with a brush, and to answer the purpose every inch of the surface 

 of the bark must be treated— a process occupying so much time that the cost of 

 the work has been found to be prohibitive, even if otherwise satisfactory — which 

 it is not. Any application that is of the nature of an air-tight coating must be 

 injurious to such a plant as tea, in which the living tissues of the bark are un- 

 protected by any corky superficial layer. If the stem of a healthy tea bush is 

 even lightly scraped with the finger-nail, the green, living tissues are at once 

 revealed. This bark contains lenCicels which are functional in the respiratory 

 processes, and any interference with their functions must injuriously effect the 

 health of the plant. It may be said that there are possibly other mixtures that 

 could be applied without interrupting the passage of the necessary gases, I have 

 as yet, failed to find any such mixture that will at the same time either act as 

 a deterrent or form a barrier against invasion by the borer. If an active poison' 

 such as arsenic, is employed, it would be necessary that an appreciable quantity 

 should be ingested by the insect. But the actual superficies of the exposed surface 

 that is operated upon by the beetle is very minute, and the perforation is very 

 generally made in the hollow of an old leaf -scar— just the very place which would be 

 most liable to escape the action of the poison. It is, moreover, extremely doubtful 

 if the material excavated by the beetle is taken into its alimentary system. It is 

 more probably merely pulverized and rejected. 



But though a direct cure has thus been shown to be improbable, I am fully 

 convinced that the pest may be not only kept in check but rendered negligible 

 by indirect cultural methods. Indeed, I have been assured that upon one estate 

 where such methods have been systematically employed, a field of tea that has 

 been continuously infested by the borer since the year 1892, is now giving larger 

 yields than it ever did before. This system is simply high cultivation, resulting 

 in a continuous healthy flow of sap throughout the plant— a condition most un- 

 favourable to the increase of the borer. In my circular on the ' Shot-hole-borer,' 



