272 THE PRACTICAL APPLICATION OF ECOLOGY 



not limit its attacks to any special season, and the bushes, except 

 for a brief period of respite after each pruning, are liable to 

 continuous infestation from the time of planting onwards. The 

 injuries entailed are caused by the tunnelling of the beetles, and 

 their larvae, in the stems and branches of the bushes. Most 

 experimental work in the past has been devoted to applying 

 insecticidal measures of control ; some have had obvious practical 

 disadvantages, and most of them have proved costly, since 

 treatment requires to be directed against virtually every bush 

 on an infested estate. 



An early observation made by Green, relative to the prevalence 

 of healed-over gallery entrances in well-cultivated bushes, led to 

 an investigation of the subject upon an experimental basis. The 

 most obvious damage caused to tea bushes by the attacks of the 

 shot-hole borer is the loss of branches, which break off at spots 

 weakened by the galleries of the insect. High winds, and the 

 movements of coolies among the bushes, are together responsible 

 for heavy destruction of this kind. It appeared feasible, therefore, 

 to discover whether it were possible to so improve the vigour of 

 the bushes as to induce rapid healing over of the gallery entrance 

 holes or " shot-holes," and so lessen the tendency of the branches 

 to break. 



After preliminary trials, field experiments were carried out at 

 Peradeniya during the three years 1923-1925, some forty plots 

 being utilised for the purpose. The treatments included two 

 experiments with nitrogenous manures, two with potassic, two with 

 phosphoric acid, and also one with lime. There were, including 

 controls, eight treatments, each being repeated on five separate 

 plots. The main result of the experiments was shown in the 

 accelerated healing of the galleries caused by the shot-hole borer, 

 which was most marked in those plots treated with nitrogenous 

 fertilisers. Healing was completed on these plots in 2-9 months, 

 as compared with 3-75 months in the controls. The authors 

 conclude that suitable manuring of tea bushes offers a ready and 

 satisfactory means of diminishing the effects of attack by the insect 

 in question, and that it should aim at increasing the nitrogenous 

 content of the soil. 



