CHAP. X.] INSECT PESTS. 79 



1)> the attack of a fungoid leaf-disease. From Ceylon the s< 

 was brought to India where it lias acquired the name oi the " Palni 

 bug " 'in account of the damage it has done in the Palnis, but it 

 lias occurred for many years on the Shevaroys and Nilgiris and was 

 introduced more recently in the Anamalais and was first noticed 

 in Coorg and Mysore in 1913 ; in the Xilgiris it lias proved a 

 highly destructive pi and it seems likely to do consider- 



able damage to the coffee industry in Mysore and Coorg. The 

 potato moth (Phthorimcea operculella) is another insect-pest which 

 has been introduced into India during recent years ; it was originally 

 brought into Bombay with seed potatoes imported from Italy and 

 has rapidly spread to practically every potato-growing district in 

 India, doing little damage to the plants growing in the field but 

 destroying the stored tubers unless special precautions are taken, 

 so that in some districts it has proved difficult or even impossible 

 to keep seed-potatoes from one season to another and very heavy 

 losses have resulted. The above are only two cases of imported 

 insects which have become serious pests when introduced into a 

 new country, but these examples are typical of many both in India 

 and abroad, and it is therefore not surprising to find that almost 

 everj civilized countrj in the world has now found it necessary to 

 impose restrictions on the importation of plants and fruits which 

 are liable to bring in such serious pests. It is sincerely to be hoped 

 that India also will very shortly be in a position to debar the entry 

 of such undesirable aliens. 



introduction of new crops and of more paying drains of 

 crops already grown has not been without .1 very pronounced effeel 

 on the incidence of insect-pests and of the damage dune by them. 

 quite apart from the introduction of new pests from abroad. It is a 

 matter of common observation that newly-introduced crops are 

 more subject than indigenous ones to the attack ol indigenous 

 insects and suffer as a rule considerably more damage. An area 

 under the Cambodia cotton plant, for instance, which is attacked 

 b\ Stem-weevil (Pempheres affinis), is usually much more badly 

 attacked than an adjacent field of desi (native) cotton and a much 

 larger percentage <>i the Cambodia plants are snapped off by a 

 strong wind. Speaking generally, on the evidence available at 

 present, then' seems to be a certain amounl of acquired immunity, 

 or at least toleration, between plants and their pest> after both 

 have inhabited the same area for a considerable period of time. 

 Tin- process may perhaps be compared to the acquired tolerance of 

 mosquito-bites exhibited by an old resident in the tn 

 againsl that shown by a new-comer and in this case also there is 

 an undoubted preference shown by the mosquitos for the blood of 



