298 



PLANT SANITATION. 



Entomological Notes. 



By E. Ernest Green. 



(Illustrated). 



The long continued drought is now making itself felt in the increase of 

 various insect pests, such as the Tea Tortrix and the "Case-worms" (Psychidce). 

 The recrudescence of the Locust pest in the Matale district is probably another sign 

 of the abnormal weather. 



Attempts to combat these pests have drawn attention to the serious evils of 

 the prevalent system of cultivating large unbroken areas of one product. With such 

 a system there is no check to the spread of a pest, nor any means of isolating a 

 particular field for purposes of remedial treatment. Under existing conditions, as 

 soon as a field has been cleared of disease, it is liable to be reinfected not only from 

 neighbouring fields but from adjoining estates which ai-e often quite undivided by 

 natural boundries. The remedy lies in the formation of belts and boundries of 

 either jungle or cultivated trees of other kinds. Such belts should be at least 20 

 feet in depth and composed of close growing trees with a good cover of foliage. An 

 undergrowth of more shrubby plants should be encouraged to complete the screen. 



In the R. B. G. Circular, Vol. II., No. 2, (Further Observations on Helopeltis), 

 published in 1902, 1 wrote: "In districts suitable for them, economic trees and plants 

 might be employed for the belts. For the larger trees, Para Rubber, Nutmeg or 

 Kola-nut suggest themselves. For the undergrowth, Croton-oil, Annatto, Castor oil, 

 or Tapioca might be used. Or the screens might consist of trees and plants, the 

 clippings of which would be suitable for green manure, such as Albizzia moluccana, 

 or " Dadap" (Erythrina lithosperma), with Crotalaria as an undergrowth." 



The above was written before the prsent boom in Rubber cultivation was 

 anticipated. Similar precautions in this new cultivation are quite as important, and 

 are in great danger of being neglected. Large areas are being planted up with Para 

 rubber, which in time will present an unbroken sheet of this one plant, offering an 

 ideal opportunity for the rapid spread of disease. Though no serious pest has yet 

 threatened Hevea, this immunity cannot be relied upon to continue. A serious 

 warning to rubber planters is urgently called for. The anticipated profits from a 

 single rubber tree are so great, that proprietors are tempted to plant up every avail- 

 able spot, and are unwilling to allow a single yard of suitable soil to be occupied by 

 what they would consider unprofitable growths. This is surely a very short-sighted 

 policy. But to meet this view I would suggest that screens composed of other 

 species of rubber (e.g., Rambong and Castilloa) might be interposed between adjacent 

 fields of Para rubber. Both the "Rambong" (Ficus elastica) and Castilloa are 

 members of the family Urticacece, while Hevea belongs to the distinct family 

 Euphorbiacece. They are consequently less likely to be subject to the same diseases. 

 An undergrowth of some kind would be required to complete the screen. The most 

 suitable plant for this must be a matter for experiment. Tea— if it would grow 

 under "Rambong" and Castilloa— would form an effective screen when allowed to 

 run up unpruned. 



Another difficulty that besets the economic entomologist in Ceylon is the 

 want of any establishment from which stocks of insecticides can be procured as 

 required. At present, if any special treatment is advised, serious delay is incurred 



