Plant Sanitation, 



rubber. The rubber trees are subject to 

 several serious fungal diseases, including 

 a canker very similar to that of the 

 cacao. Sections of trees, said to have 

 been killed or injured by boring beetles, 

 are repeatedly sent in to this Depart- 

 ment, but a careful examination of the 

 specimens has invariably revealed the 

 presence of one or other of the fungal 

 diseases. In no instance have borers 

 been found in sound healthy bark. A 

 healthy rubber tree is protected from 

 boring insects by the viscid latex which 

 exudes from any wound and overwhelms 

 any insect intruder. In the incipient 

 stages of canker only the superficial 

 layers of bark are involved. Borers will 

 attack these spote and will attempt to 

 gain an entrance : but, as soon as they 

 reach the deeper and as yet unaffected 

 layers of bark, they are repelled by the 

 flow of latex. In later stages of the 

 disease, when the whole thickness of the 

 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 perfor- 

 ations and flowing down the stem. This 

 is often taken, by the planter, 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, where 

 only the superficial layers of the 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 limit of 

 the diseased layer. 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 

 the bark is pierced by shot-hole borers, 

 the latex finds 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 exces- 

 sive drought or over-tapping. Should 

 this happen, a shower of rain might 

 result in renewed activity and bleeding 

 through the perforations would occur. 

 The exudation of latex and presence of 

 boring beetles may usually be looked 

 upon as a valuable indication of inci- 

 pient disease, thus allowing of early 

 treatment before the disease has become 

 deep seated. 



The original gallery constructed by 

 Shot-hole Borer beetles is not primarily 



38 [January, 1912. 



for feeding purposes. It is constructed 

 as a safe nidus for the eggs, which are 

 deposited at the ends of the galleries. 

 In the case of Bostrichids and the greater 

 number of Scolytids, the young larvse 

 extend the parent gallery while feeding 

 upon the woody tissue. But there is a 

 small section of Scolytidce which have 

 a different habit. These are the species 

 that attack living plants, and they have 

 been called 'Ambrosia Beetles,' by the 

 American Entomologists, from the fact 

 that they cultivate, in their galleries, a 

 particular fungus known as ' Ambrosia 

 fungus,' upon which the larvse are 

 nourished. These particular beetles, 

 therefore, do not feed upon the wood at 

 all. In such cases the injury to the 

 plant is the result, primarily, of a 

 partial interruption of sap due to the 

 position of the parent galleries, and 

 secondarily to an invasion of destructive 

 fungi through the perforations. 



The galleries of the 'Ambrosia Beetles,' 

 are purposely constructed in such a 

 manner that the normal flow of sap is 

 interrupted. The shot-hole borer of the 

 tea plant runs a circular gallery round 

 the branch, just beneath the cambium, 

 thus partially ringing the branch. An 

 exudation of sap occurs upon the walls 

 of the tunnel, forming a medium for the 

 development of the Ambrosia fungus. 



It has been suggested that the canker 

 of our Hevea trees may be originated 

 by spores carried into the bark by the 

 beetles themselves. This idea is a plau- 

 sible one, but is not supported by the 

 observed conditions. Canker often 

 occurs without the presence of the 

 beetles, but I have not yet seen perfor- 

 ations by the beetle unassociated with 

 fungal disease of some kind. The exud- 

 ation of rubber latex, in healthy bark, 

 not only repels any inexperienced in- 

 truder, but effectually seals up the 

 wound and prevents invasion of fungus. 



I append a list of the species of Scoly- 

 tidse that I have found associated with 

 various economic plants in Ceylon. I 

 am indebted to Col. Winn-Sampson for 

 the determination of the species. 

 Xyleborus fornicatus, Eichh. 



In living stems and branches of Tea, 



Psidium, Ricinus, and Albizzia mo- 



luccana. Also in diseased branches 



of Hevea. 

 Xyleborus brevis, Eichh. 

 In dead and diseased stems of Gre- 



villea and Albizzia. 

 Xyleborus asperatus, Bldf . 

 In dead branches and stems of 



Albizzia. 

 Xyleborus semiopacus, Eichh. 

 In dead stems of Tea, Eucalyptus, 



Hevea and Grevillea, Occasionally 



