THE PESTS AND DISEASES OF THE CANE. 



8. Quarantine of imported Plant Material. It is certain that many of the 

 serious epidemics of insects are due to their accidental importation unaccom- 

 panied by the natural enemies that keep them in check in their original 

 habitat. Instances of these introductions are numerous. The 'Borer' was thus 

 introduced into Mauritius in 1848 15 in a consignment of cane received from 

 Ceylon. Orders were given to destroy the cargo, but it is supposed that 

 some ill-advised person secretly removed and planted a few tops. The intro- 

 duction of canes from abroad also accounts for the Weevil Borer and Leaf 

 Hopper in the Hawaiian Islands. It is of great interest to note that evidence 

 exists that the borer of these islands was introduced from Otaheite along with 

 the original Lahaina cane (cf. Chapter TV.)] it was on the "Pioneer" estate 

 at Lahaina that it was first noted a year or two after the introduction of the 

 cane there. Another boring pest of the cane, Sesamia nonagrioides, originally a 

 North African species, has now become widely distributed over the tropics. 



When the immense damage done by insects is recollected (in the Hawaiian 

 Islands alone the leaf hopper in one year destroyed cane equal to not less than 

 60,000 tons of sugar), any expenditure on a proper system of quarantine can 

 only be regarded as a rational policy of insurance. Such a system is now 

 established in the Hawaiian Islands. 



9. Infection with Disease. A number of years ago it was proposed to 

 destroy rats by means of bait infected with cultures of the organism Septicaemia 

 muris ; the first essays in this direction were not attended with success, but 

 more lately favourable reports have been received of the efficacy of ' Dansyz 

 virus ' as a muricide ; the use of this has, of course, been chiefly developed in 

 connection with the prophylaxis of plague. 



A number of micro-organisms are parasitic upon insects ; thus the death 

 of the weevil borer has been observed as due to the mould Penicillium glaucum ; 

 a fungus, Isaria barber i, is also known as parasitic upon the caterpillar of the 

 West Indian moth borer, and a species of Botrytis upon the caterpillars of the 

 moth Psalis securus in Java. The help afforded by these fungi does not appear 

 to be very great. The destruction, however, of the scale louse Aleyrodes 

 longicornis by a fungus Ascherontia aleyrodis in Florida has been noted by 

 Webber 16 apparently acting with good effect. 



10. Encouragement of natural Enemies. The increase of many pests is 

 often traceable to a decrease in the number of their enemies ; an example of 

 this is the great increase of the mole cricket in Porto Rico in 1876 9 after the 

 destruction of the avian population of that island in a hurricane. Amongst the 

 insectivorous animals which may be classed as friends of the cane are birds, 

 lizards, newts, toads, ladybirds and spiders. In this connection Dr. Perkins 

 informs the writer that the destruction of the ' grass army worm ' in the 

 Hawaiian Islands is due largely to the mynah bird, an introduced species. 



11. Parasitization. If the checks on insect multiplication were removed 

 agriculture would be impossible. To the great majority of insects are attached 



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