696 rEOCEEDINGS OF THE THi:.!) ENTOMOLOGICAL MEETING 



35.— SOME PROBLEMS IN FOREST INSECT CONTROL. 



By C. F. C. Beeson, M.A., I.F.S., Forest Zoologist, Forest Research 

 Institute, Deha Dun. 



In order to appreciate the position of forest insect control in relation 

 to the study of forest entomology generally, it is necessary to recognize- 

 certain fundamental characteristics in the constitution of the forests of 

 British India, and in the methods hy which they are managed. 



The first striking character is the absence of epidemics of primary 

 pests, that are capable of killing ofi healthy, hving, trees over large areas. 

 The forests of Central Europe have for the last century suffered consider- 

 ably from fatal outbreaks of lepidopterous defoliators and boring beetles. 

 The forests of the United States and of Canada have to contend against 

 serious epidemics of caterpillar and saw-fly pests and the depredations 

 of bark-beetles, which accompany fires and lumbering operations.* 



In British India, on the contrary, no primary pests are known that 

 are capable of killing healthy trees in natural forest and no secondary 

 pests have increased to epidemic incidence and completely destroyed 

 appreciable areas of pxire forest, or even all the inchviduals of one tree- 

 species in a mixed forest. The factors contributing to the absence of 

 epidemics are complex, but they arise from the existing ecological condi- 

 tions of the forests, and from the methods by which they have been 

 worked since the time of their reservation. 



It is not possible to define the peculiar conditions more precisely 

 in this paper, but, in illustration of the absence of any tendency to 

 epidemic development of pests in natural forests, the following cases 

 may be cited. 



1. The sal, Shorea robusta, is the foodplant of a heartwood borer, 

 Hoflocerambyx spinicornis, which normally breeds in dead or diseased 

 trees. Recently a locahzed endemic outbreak of this borer has occurred 

 in a sal forest in the United Provinces, and a large number of trees has 

 been killed annually by direct preliminary attack. The area of the 

 infestation is small, some 7 square miles ; the annual death-rate varies 

 from 8,000 to 12,000 trees, but the total mortality represents only a small 

 percentage of the growing stock. The forest has been under close 

 observation for three years and it has been found that the progress of 

 the attack is extremely variable throughout the area. In a given unit 

 area, say 100 acres, the rate of increase of the pest, expressed in the 

 number of trees killed, may rise from three to ten times, and then 

 decrease to a half or a tenth in a period of four years ; in other words, 



* Tide Beeson, C. F. C, " Forest Insect conditions in India." Agric. Jourl. India, 

 Special Indian Science Congress Number, 1918, pp. 114-124. 



