146 CHAPTER IX 



\n a consignment of cane from Ceylon. The infection of the canes was 

 observed, and orders were given for their destruction. It is believed that 

 $bme ill-advised planter surreptitiously obtained cuttings and planted them 

 in the Flacq district. 



5. In Porto Rico in 1876, consequent on the destruction of the avian 

 population by a hurricane, the mole cricket, Scapteriscus didactylus, caused 

 great damage not only to cane but to all crops. 36 



6. Early in the twentieth century the " leaf hopper," an asciracid, 

 iPerkinsiellia saccharicida, appeared in Hawaii, 29 and for three or four years 

 'aid great damage. Undoubtedly this pest arrived ^from Australasia. The 



story of this epidemic and its control forms a classic in economic entomology, 

 and is discussed at length elsewhere. 



7. About 1910 serious damage was observed in certain parts of Mauritius, 

 the cause being ascertained to be due to the larva of a root-eating lamellicorn 

 beetle, Phy talus smithi. 2Z This pest had been introduced with cane from 

 Barbados, and in the latter island its presence was barely known owing to 

 efficient parasitization. 



8. At the same time the observation recorded in (7) was paralleled in 

 Hawaii by the appearance of another lamellicorn root-eater, Anomala sp. 

 In this case the introduction was from Japan, and was not connected with 

 cane importations. Similarly also, the pest was barely recognised as present 

 in Japan. 21 



9. About 1901 a long-continued borer epidemic began in British Guiana. 44 

 This was caused by the " large " or " giant " moth borer, Castnia licus. 

 In distinction to some of the other epidemics recorded, this was caused by 

 an indigenous pest. The habitat of this insect is from Central America 

 to the Amazon, and previously it had only been recorded as feeding on the 

 roots of certain orchids near the upper Orinoco. For some obscure reason 

 it suddenly developed the habit of attacking cane. 



THE " NATURAL CAUSES " AND " NATURAL CONTROL " 

 OF INSECT EPIDEMICS. 



The rate at which insects multiply is very great, a single female producing 

 several hundred eggs. Unless there were some controlling factor limiting 

 the increase of insects agriculture would be impossible. The most important 

 one is to be found in parasitism, whereby one insect, a crop predator for 

 example, acts as the host for a parasite which lives on and destroys its host. 

 In this way a " natural balance " is maintained. 



This observation offers an explanation of the cause and course of insect 

 epidemics. In the first place an insect with predaceous habits is introduced 

 into a district and arrives there unaccompanied by the parasites which 

 restrain its developments in its original habitat. Its multiplication now be- 

 comes so rapid that in a short time an intense insect epidemic occurs. Gener- 

 ally when discussing introductions two distinct conditions may be recognised. 

 The locality of introduction may be continental, in which case there is likely 

 to be a very ample local fauna, which may contain insects parasitic on the 

 introduced species, or insects which in a short period of time may develop 

 .the faculty of parasitization. 



In this case a severe epidemic is unlikely, or the introduction may even 

 pass unnoticed. This statement is not, however, to be construed as implying 

 that insect damage may not be great in a continental area. In British 



