112 TB IN ID AD AND TOBAGO BULLETIN. [XIX. 3. 



Development of Injury. 

 A number of observations were made this year to determine more 

 accurately the development of the injury to the leaves, both by watching 

 carefully the development of individual punctures on the leaves and by 

 observing the difference in time between the greatest abundance of 

 froghoppers of one brood and the greatest visible blight. Some of 

 the results were obtained early enough to be incorporated in my 

 full report. 



A known number of froghoppers were sleeved on four cane stalks 

 on October 15-18, 1920 for one or two nights and then removed. On 

 these plants one hundred and twenty-two streaks developed and the 

 course of most of them was noted every three to six days. 



During the first week most of the streaks remained pale and 

 discoloured (Stage I see Report p. 21), but by the end of the week 

 had begun to show the red discoloration at the point of injury (Stage II). 

 This red discoloration continued to spread during the next ten days and 

 by the end of the third week, most had the dead centre typical of 

 Stage III. After this the injury continued to spread slowly till the 

 death of the leaf. 



Stage I. From 2nd to Ttli day (some lasted as late as 15th — some 



ended as early as 4th). 

 Stage II. From 7th day (varying as above) to 18th day (some as 



early as 13th, others as late as 26tb). 

 Stage III. From 18th day (varying as above) to death of leaf. 

 The 122 streaks which developed were produced by the equivalent 

 of 50 adults sucking for one night, so that it will be seen that each 

 adult is responsible for an average of 2^ punctures per night. 



The froghopper appears to prefer the leaves which have just unrolled 

 as the follo\\ing figures show : 



Total 2'i'uictures 



on centi-e rolled leaf ... ... ... 13 



on first (youngest) open leaf ... ... ... 41 



on second leaf ... ... ... ... 22 



on third leaf ... ... ... ... 13 



on foiu'th leaf ... ... ... ... 11 



on fifth leaf ... ... ... ... 12 



on sixth leaf ... ... ... ... 1 



Observations in the field indicate that the greatest damage is about 

 three weeks after the height of the brood, provided that severe dry 

 weather and consequent root disease development does not intorvene. In 

 normal cases the plant is able after this time to replace by new 

 undamaged growth the loss due to the s]:)i-ead of injury, and recovery 

 sets in. 



liAINFALL AND P>U00DS. 



The dates of the brood correspond exactly to what would have 

 been expected from the data given on p. 62 of my rejDort. 

 The first continued rains of the wet season started about June 

 15-] 8; the first brood was at its height about August 11; 

 the second brood about October 8, and the third about 



