THE PESTS AND DISEASES OF THE CANE 153 



Of a different nature are the conditions observed by Walcott 56 in Trinidad 

 in connection with the froghopper. He noted the ill-kept conditions 

 of the fields and the large areas of grass-grown land in close proximity to the 

 canefields. Regarding the froghopper as originally feeding on grass he 

 considers these areas as foci of infection. These observations recall the 

 comments made by Guilding 11 in 1834 in reference to the moth borer : 



" Those animals which the Creator has thought fit to form and preserve 

 for ages man will not be permitted to exterminate ; we may, however, with 

 propriety, strive, and by all means in our power, to lessen the number of those 

 creatures which injure or destroy our property. Those animals, when they assail 

 us in moderate numbers, act only as a stimulus, wisely sent to arouse the inattentive 

 planter to cleaner and more careful modes of husbandry. When they swarm 

 so as to deprive him of his crops, the loss must be in future attributed either to his 

 obstinacy or to his negligence." 



A number of years ago the advice was very frequently given that the 

 burning of trash would destroy the breeding places and at the same time 

 the pests themselves. It is now recognised that this advice is bad. Perkins 29 

 in particular has shown that the leaf hopper is able to escape by flight, but 

 that many of its parasites fail to do so. Similarly, and for the same reason, 

 Van Dine 57 attributes the comparative freedom of Cuba from insect damage 

 to the practice of cutting without burning, and of leaving the trash to rot 

 on the land, as compared with the opposite custom in Porto Rico, where the 

 damage is much greater. 



7. Cultivation. In the case of root eating grubs, ploughing at the appro- 

 priate season will result in bringing many to the surface, where they may be 

 eaten by birds, including domestic poultry. Such a scheme is followed in 

 the control of the cane grub in Australia, and in India in connection with 

 a grasshopper, Hieroglyphus frucifer. 



8. Quarantine of Imported Plant Material. The instances already 

 quoted show how great may be the danger of an unrestricted importation 

 of cane. The Territorial Government of Hawaii established a system of 

 inspection a number of years ago, and the Federal Government of the 

 United States has absolutely prohibited the importation of cane. To a 

 certain extent so stringent a ruling is to be deprecated since a district may 

 wish to obtain a new and valuable variety. While the uncontrolled im- 

 portation of cane is to be unreservedly condemned, the danger of importing, 

 under rigid inspection and isolated and protected propagation, the single 

 cutting necessary to establish a variety reaches the vanishing point. 



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

 destroy rats by means of cultures of organisms producing specific rat diseases. 

 One of the most widely used preparations was Dansyz virus, but the results 

 have been contradictory. 



10. Encouragement of Natural Enemies. This heading is really included 

 under the term " natural control," which is, however, restricted more or 

 less to specialized parasitization. The natural enemies of insect life include 

 birds, lizards, toads, newts, lady-birds and spiders. Amongst the natural 

 enemies of rats should be included snakes, and their beneficial action on a 

 sugar plantation was noted by Dutr6ne as early as 1790. 



