22 BULLETIN" 256, U. S. DEPARTMENT OF AGRICULTURE. 



Plats 1, 2, 4, and 5 received two applications containing lime-sulphur 

 and arsenicals and one application of lime-sulphur alone ; plats 3 and 6 

 received one application containing both lime-sulphur and arsenicals 

 and two applications of lime-sulphur alone; plats 7, 8, and 9 received 

 only two applications of arsenicals alone. The chief purpose of adding 

 lime-sulphur to the sprays was to make them effective against the 

 citrus thrips. The third application was directed solely against this 

 insect, only two applications of arsenicals being made in any case. 

 The applications were timed, also, partly with a view to controlling 

 thrips as well as katydids, and the dates of beginning were May 22, 

 June 3, and June 24, respectively. 



Results. 



The efficiency of the sprays in killing katydids was determined by 

 a comparison of the number of living insects occurring in the sprayed 

 and unsprayed blocks some days after spraying was completed. 

 Arsenite of zinc at the rate of 2 pounds per 100 gallons killed 93.1 

 per cent of the fork-tailed katydids and 100 per cent of the angular- 

 winged katydids. Arsenate of lead at the rate of 4 pounds per 100 

 gallons killed 100 per cent of the insects in each case. 



The results of the season's spraying work were principally mani- 

 fested in three ways: (1) By preventing a complete loss of a certain 

 amount of fruit by dropping; (2) by almost complete prevention of 

 katydid injury to the mature fruit and the leaves and reduction in 

 the amount and severity of thrips injury; and (3) by improvement 

 in the amount and vigor of growth of the sprayed over the unsprayed 

 trees. 



PREVENTION OF DROPPING. 



During July, fruits injured by both katydids and thrips were very 

 conspicuous on the unsprayed trees, at once attracting the attention 

 when one entered the orchard. While in the orchard on August 9 

 the senior writer noted that badly injured outside fruit was decid- 

 edly less in evidence on unsprayed trees than had been previously 

 the case. The cause of this disappearance of fruit was soon found; 

 it had fallen to the ground. By counting all the fruit on and under 

 10 unsprayed trees it was found that 18.7 per cent of the crop had 

 fallen from these trees. Examination of the fruit which had fallen, for 

 the location of the insect injury, disclosed 62.8 per cent of it full of 

 holes, while 83.3 per cent were severely marked by thrips. Many of 

 these fruits had been eaten into near the point of attachment to the 

 stems. However, much of the dropped fruit during this period was 

 caused by thrips injury, the most severe dropping due to katydids 

 coming earlier in the season when very small fruits were chewed to 

 pieces by these insects. At all events, the 18.7 per cent of dropped 



