78 SOME SOUTH INDIAN tNSEt rS, ETC. [("HAP. X. 



and plants arc often so complex and the balance ol life is so deli- 

 cately adjusted that the extinction of one tree or plant, for example, 



ad to the extinction of certain insects dependent on that 

 particular tree or plant, and the extinction of such insects may have 

 an important effe< t on other insects or plants which at first sight 

 would not seem to be affected; but the chain of interrelationships 

 long and complex so that the breakage of a single link 

 gives rise to quite unexpected results. ( >ne effect of disafforesting 

 an area which would seem obvious is that various insects, deprived 

 of their food in the forest, would invade adjacent cultivated areas ; 

 antl this may happen to some extent, hut probably far less often 

 than is supposed. The fauna ^nd flora of a truly forest area and 

 those of a disafforested area recentl} placed under cultivation are 

 usually very sharply differentiated and this difference m 



ii in the Mill Districts of Southern India and still more dis- 

 tinctly in other parts of the world, such as the larger islands of the 

 Seychelles where there is a very strongly demarcated line between 

 the insect-fauna of the primeval jungle and that of the cultivated 

 area immediately adjacent. The real influence of destruction of 

 forests on the incidence of insect pests in their vicinity is almost 



- indirect hut it is no less important for that, and the preserv- 

 ation of forests, certainly in all Mill Districts, should he looked on 

 as a national affair of the first importance. 



The introduction of non-indigenous pests from other countries is 

 i vi i <. fertile source "l trouble and especially so because such pests 

 are usually brought in by themselves without the enemies which 

 have normally kept them in check and thus they are abb- to 

 increase very rapidly, so that an insert, u huh in its native country 

 Iocs little or no harm, when introduced into a new country or 

 locality, may increase to such proportions as to become a pest. 

 This tendency is not confined to insects but is exemplified by 

 numerous animals and plants in all parts of the world and it is 

 bei muing almost an axiom that the worst pests of any country are 

 introduced ones. The rabbit and thistle in Australia, the mongoose 

 in the West Indies, Lantana and the green scale (Lecanium viride) 

 in Southern India, are all well-known instances of introduced 

 organisms which have become serious pests in the new countries to 

 whichi 1 taken. The green scale is believed to have been 



from Brazil by waj of Ceylon. It is interesting to note 

 th.it it was quite unknown in [86l to J. Xietner, an entomological 

 Coffee-planter in Ceylon, who wrote a comprehensive series of 

 " Observations on the Enemies of the Coffee Tree in Ceylon "; yet 



within twenty years it had gained such a footing as to lead to the 

 ruin of the coffee plantations which had already been weakened 



