PROCEEDINGS OF THE THIRD ENTOMOLOGICAL MEETING 69T 



the intensity of attack is constantly shifting its foci, with a general 

 trend from the highly attacked locahties to those in which the incidence 

 is lower. The effect of the attack of the insect on the forest approxi- 

 mates to a heavy thinning but never to a clear felling. 



One might be tempted to consider this instance as a case of serious 

 damage by an insect pest, but the forest has also received attention from 

 the sylvicultural aspect and has been diagnosed as much over-stocked 

 and in a generally unhealthy condition. Thinnings are being made in 

 accordance with modern sylvicultural principles and a far greater number 

 of trees is being removed by these operations than by the insect. 



2. A second instance may be taken from the Sunderbans. In 1909 

 a cyclone blew down several thousand simdri (Heritiera Fames) trees. 

 The normal consequence of such an occurrence in the forests of Central 

 Europe would be an epidemic outbreak of woodborers and bark-beetles. 

 No epidemic occurred in the Sunderbans and attack by shothole borers 

 and bark-beetles was confined entirely to trees with diseased roots along 

 the banks of water channels and islands. 



3. A third illustration is foimd in the sal forests of the Duars, where 

 an abnormal mortality of sal was reported five or six years ago. On 

 investigation the dead trees were found to contain a. mixed fauna of 

 heartwood and sapwood-beetles and shothole borers. Careful enu- 

 meration failed to show a preponderance of one species to which the 

 blame for primary attack could be assigned, while the presence of an 

 appreciable proportion of dead trees without insect attack led one to- 

 suspect other agents as the primary cause of death. This was even- 

 tually discovered in the form of a root fungus, which was itself conse- 

 quent on unfavourable conditions of soil-aeration. 



While emphasizing the immunity of Indian forests from epidemic 

 outbreaks of insects I do not wish to imply that injury from secondary 

 pests is equally neghgible. The existence of insects capable of causing 

 technical damage to timber or of producing loss of increment and delayed 

 growth is an indisputable fact. It is becoming annually more evident 

 that these insects will in the future be capable of causing serious loss, 

 and there are also indications that several species now of secondary 

 importance will modify their habits and take on the role of primary 

 pests. 



But at the present moment the need for the wholesale control of 

 insects injuring forest trees has not yet arrived. Injury due to insects 

 is only one factor causing loss of forest capital. The other factors are 

 more easily and more profitably controlled than the insect factor, and 

 require to be ehminated before the latter can be considered as a. 

 practical measure. 



