700 PROCEEDINGS OF THE THIRD ENTOMOLOGICAL MEETING 



A second possibility of control lies in the conduct of thinnings : — 



(1) In order to kill the borers present in infested trees, the most 

 favourable time to fell is in November or December. The feUing of 

 trees should therefore be carried out shortly after marking. 



(2) We have discovered that the liabiHty to attack is proportional 

 to the girth of the tree and is independent of its state as a dominant, 

 dominated or suppressed tree. 



The incidence of the borer can be reduced, therefore, by felhng all 

 suppressed trees marked in a sylvicultural thinning instead of leaving 

 them to die. 



(3) The more frequently thinnings take place and the greater the 

 proportion of large-girthed trees removed the more marked is the reduc- 

 tion in the absolute numbers of the borer. Beyond a certain point, 

 however, these two factors are adverse to the development of the maxi- 

 mum yield in the crop. We have now to determine the point at which 

 the advantages in one direction balance the disadvantages in the other 

 direction. 



A third control measure lies in the isolation of pure stands of teak 

 by belts or blocks of other species in order to delay the introduction of 

 the borer and to restrict its subsequent development. Here again we 

 have methods which favour the control of the hoiei opposed to 

 sylvicultural and economic principles. 



The collection of statistical data is at present directed to the elucida- 

 tion of these points. 



The beehole borer is an example of a pest with an annual hfe-cycle 

 and one known food-plant ; the next type to be considered is that of a 

 pest with several generations in the year and several host-plants. 



2. The Shoot and Fruit borer of Toon. 

 The shoot and fruit borer of toon, Hypsipyla robusta, Moore. (Fam. 

 Pyralidse), has an annual cycle of five generations. The caterpillars 

 of the first generation feed on the flowers of the tree ; those of the second 

 generation on the fruits, and the remaining three generations bore 

 inside the green shoots of the current year's growth. Its importance 

 as a pest lies in the damage done by the broods attacking the shoots. 

 The leading and lateral branches of young trees and saplings are killed 

 ofi to so complete an extent that the season's growth is entirely nulli- 

 fied, and the development of the sapling is checked for many years. 

 Eventually one or two leaders in the bushy broom-like formation escape 



