150 FROGHOPPER BIJGHT OF SUGAR-CANE. 



INTRODUCTION. 



The Sugar-cane cultivation of Trinidad covers an area of about 78 

 square miles, out of a total area of 1,750 for the island. The crop has 

 varied from 38,000 tons to 71,000 tons in the past tv^enty-one years. 

 The rainfall is about 64 inches, with a dry season from January to May 

 and a wet season from May to December (fig. 1). The crop is cut 

 during the dr3' season. Three or four crops are usually cut before 

 replanting, (p. 11.) 



The growing canes have been subject for many years to outbreaks 

 of a disease locally known as "Blight" or " Froghopper Blight," which 

 consists essentially of a browning and drying up of the leaves and a 

 check to the growth which may result in the total loss of the crop. 

 The loss during the past fifteen years has probably averaged £50,000 

 per annum and in 1917-1918 reached about ^£300,000. The insect 

 Tomasjns saccharina. the sugar-cane froghopper, is almost invariably 

 found in abundance in the blighted fields, as well as various species of 

 root fungi, and both have been held responsible in varjdng degrees for 

 the danaage. (p. 13). 



Conditions similar to the froghopper blight were reported in 1863, 

 but it was not until 1889 that the froghopper was discovered by 

 Hart and its connection with the damage suspected. In 1906 a 

 severe outbreak called attention to the subject once more and during 

 the next three years, all of which were characterised by severe blight, 

 various opinions were held as to the relative importance of the frog- 

 hopper and root disease In 1909 regular investigation was started by 

 the Board of Agriculture and Borer, Urich and Guppj- studied the varied 

 aspects of the problem. The life his.ory of the froghopper was worked 

 out, two egg-parasites were found, and the green muscardine fungus 

 which destroys the adult, was cultivated on a large scale. In 1910 and 

 1912 Gough and Kershaw continued the investigations. The former 

 discovered the Syrphid Fly, which deslroj's the nymphs, and the latter 

 recommended the search for a more efficient parasite outside Trinidad, 

 (p. U). 



During 1916 and 1917 I made a search for such parasites in British 

 Guiana, Panama and Costa Eica. New froghoppers were found in all 

 these countries, but the enemies were found to be the same as those 

 already known in Trinidad. The range of the parasites is evidently 

 much greater than that of their hosts. In Panama a few specimens of 

 a new egg-parasite were obtained but they died before any attempt could 

 be made to breed them. In .July 1917, owing to the great difficulty of 

 carrying on the work single-handed and with the prevailing conditions of 

 transport, I returned to Trinidad to study the pest in the island, (p. 16). 



In 1918 and 1919 Nowell. emphasized the relation between local 

 infestations and the condition of the soil, and advocated the application 

 of agricultural methods to the reduction of blight, (p. 18). 



THE NATURE OF THE BLIGHT. 



Damage usually first appears six weeks to two months after the 

 beginning of the wet season and the canes stop growing, and the leaves 

 wilt and are streaked with brown marks. After some weeks recovery 

 sets in, usually to be followed by a second and occasionally a third attack 

 at intervals of about two months, (p. 20). 



From each puncture of the adult froghopper on the leaf an elongated 

 area of injury spreads, at first pale and later brown. Increase in size 

 of this spot may continue for as long as four or five weeks and, from 



