1910.] FBOGHOPPEE BLIGHT OF SUGAR CANE. 53 



found among canes that are attacked by Froghoppers, and ia usually 

 absent when the canes are not affected" and later " It is ro.v generally 

 accepted that insects .... attack canes infested with fungus disease 

 more rapidly than healthy plants, and that inclement seasons lead to 

 the spread of diseases and consequently to attacks of insects." 



Collens in the same year {Proc. Agr. Soc. Vill. £63) writes that the 

 cane " is first attacked by disease and efforts to .... throw off . . . . 

 are rendered ineffective by persistent attacks of froghoppers." 



Carmody {Proc. Agr. Soc. IX. 1909. 107) writes " whenever Frog- 

 hoppers are unusually abundant, the canes on closer examination have 

 been found to be diseased from other causes, and the juice is abnormally 

 acid." He suggests that the acid juice may make the canes more 

 attractive to the Froghoppers. 



On the other hand other authorities were convinced that the 

 Froghopper is the chief cause of the damage. J. Black {Proc. Agr. Soc. 

 YIII. 1918, 565) writes "I have seen no case of blight where the 

 froghoppers have not first been present in large numbers." J. B. Borer, 

 who had just started his work as Mycologist to the Board of Agriculture 

 writes (Report of the Mycologist August 13, 1909) " The disease called 

 blight here is quite distinct and different from the root fungus in many 

 ways .... In many worst blighted fields root fungus is present only 

 in very small quantities, or is altogether absent." F. W. Urich, 

 Entomologist to the Board of Agriculture writes {Bull. Dcpt. Agr., 

 Trinidad and Tobago. IX. 17) " canes attacked by root disease, as 

 well as those entirely free from it, were blighted .... In every case 

 Froghoppers were present." 



From this time onwards, until quite recently, during the investiga- 

 tions of Messrs. Rover (1909-18), Urich (1909-1919), Gough (1910-1911), 

 Kershaw (1912-13) and Guppy (1912-14), more and more attention has 

 been paid to the role played by the Froghopper and research was almost 

 entirely directed to its reduction or control. It is true that Gough 

 in his final report {De])t. Agr., Circular No. S. 1912. 11) says "there 

 is evidence to show that fungoid diseases of the cane predispose it tO' 

 an attack of Froghoppers," but apart from this there is scarcely any 

 further reference to the possible association of the two diseases. 



During the first eighteen months of my own work on the Froghopper 

 (1916-1917) I was working, by instructions, on the introduction into 

 Trinidad of new enemies to reduce its numbers, and during that time 

 I had a few opportunities of studying the blight in the cane fields. 



In August 1917 it was decided to abandon, at least temporarily, this 

 branch of the work and I was instructed to study the Froghopper in 

 Trinidad " from a wide biological standpoint." 



The year 1917 was unfortunately marked by a very severe outbreak 

 of bhght, and I soon found that, although Froghoppers were invariably 

 present in blighted fields, yet there was not a strict correlation between 

 the numbers of insects present and the extent of the damage. Certain 

 fields appeared to survive a severe infestation of froghoppers, while 

 others with much fewer were severely damaged. This disparity became 

 very obvious when an attempt was made to find how many Froghopperi 

 were required to cause damage. 



