630 RUBBER 



bark is involved, latex is absent from the diseased tissues, 

 and there is no hindrance to the progress of the insect, 

 which can then perforate the bark with impunity, and even 

 extend its galleries into the wood itself. 



It sometimes happens that latex is found to be exuding 

 from the perforations and flowing down the stem. This 

 is accepted, by some planters, as proof positive that the 

 beetle has attacked healthy laticiferous bark. But the 

 phenomenon is explicable in other ways. In the early 

 stage of the disease, when only the superficial layers of 

 bark are affected, latex may exude from the deeper tissues 

 through the abandoned galleries of insects that had 

 attempted to push their work beyond the danger zone. 

 Another cause of " bleeding " may result from the 

 separation of dead bark from the wood, leaving a cavity 

 which often becomes filled with latex from surrounding 

 healthy tissues. If the dead bark is imperforate, the 

 latex coagulates and forms a pad; but if it has been 

 pierced by borers the latex will find its way to the 

 surface. It is possible even that borers might attack 

 otherwise healthy bark during a temporary cessation of 

 activity in the laticiferous vessels resulting from excessive 

 drought or over-tapping. Should this happen a shower 

 of rain might induce renewed activity, and bleeding 

 through the perforations would then occur. The 

 exudation of latex and the presence of boring beetles 

 may be regarded as a valuable indication of incipient 

 disease, thus allowing of early treatment before the 

 disease has become deep-seated. Similar conditions have 

 been observed in other countries. Dr. Aulmann, in 

 " Die Fauna der Deutschen Kolonien," speaking of 

 Xyleborus affinis in the Cameroons, remarks that only 

 trees depleted of sap by tapping are attacked, as the 

 beetles are killed by the flow issuing through the bore- 

 holes made on full-sapped trees; and adds that careless 

 tapping exposes the wood and favours attack. 



Lepidoptera. 



No very serious caterpillar pests of Hevea have been 

 recorded, though several species are known to feed 

 occasionally on the foliage of the plant. Amongst these 



