62O RUBBER 



valuable memoirs on the subject, and it is to their writings 

 that I am indebted for my information. 



It appears that T. gestroi is chiefly dependent upon 

 dead and decaying timber for its maintenance, but 

 that from these centres it will extend its ravages to 

 living trees of certain species, of which Hevea is, unfor- 

 tunately, one. Even in such cases it attacks only the 

 inert heart-wood, hollowing out the larger roots and the 

 base of the stem, but leaving the functioning outer tissues 

 intact. Damage to the tree is consequently the result 

 of a weakening of its natural support, leaving it powerless 

 to resist any external strains. Affected trees are broken 

 off or overturned by the slightest excess of wind pressure. 

 The only fact that lends some supposition to a theory of 

 primary infection by fungus is that a certain selective 

 action appears to occur, individual trees being neglected 

 in the midst of thickly infested areas. But against this 

 suggestion is the statement that the bark and functioning- 

 tissues of the tree remain healthy, even when the heart- 

 wood has been more or less completely destroyed. The 

 extent of the damage that can be effected by this pest 

 is shown by a statement of Mr. Pratt, who reports that 

 within a certain area of fifty acres 70 per cent, of the 

 trees had been attacked by T. gestroi. In another case, 

 from fifteen to twenty trees in the immediate vicinity of 

 a nest had been destroyed. The work of T. gestroi is 

 most insidious, the trees being usually injured beyond 

 recovery before there are any outward indications of the 

 presence of the enemy. Queens of this species are very 

 rare, or extremely difficult to find. The main centre of 

 the colony is usually at a considerable distance from the 

 point of attack, but Pratt has shown that it may be dis- 

 covered by following up the galleries of the insect, which 

 almost invariably lead to a nest in some decayed log or 

 buried stump. Should the gallery become obliterated in 

 the course -of excavation, its direction may be picked up 

 by cutting a trench at right angles to the line. The 

 termites will then construct covered ways connecting the 

 severed ends of the passages. When the headquarters 

 are discovered the nest should be destroyed by fire. The 

 employment of a fumigator is strongly recommended. 



