10 



INSECTS INJURIOUS TO SUBTROPICAL, FRUITS. 



FUMIGATION. 



Some experiments have been conducted in the hope that fumiga- 

 tion with hydrocyanic-acid gas would prove effective in controlling 

 the orange thrips, but all results have been unsatisfactory, because 

 of the activity of the insects, the large number of generations, and the 

 expense of the operation. 



SPRAYING. 



The only method of control which has given good results is spray- 

 ing at high pressure Avith a contact insecticide. No sprays aside from 

 those which kill by contact have been tried because such sprays have 

 been unsuccessful in controlling other species of injurious thrips. 



Experiments to Determine Killing Effect of Different Sprays. 



The following spra^^s were tested in the field for killing effect on 

 the thrips: Homemade distillate-oil emulsion, in combination with 

 black-leaf tobacco extract, which is a dark, almost viscid liquid con- 

 taining 21 per cent nicotine; and commercial lime-sulphur (33° 

 Baume) in combination Avith the tobacco extract. All sprays were 

 applied with a hand pump, maintaining a j)ressure of 140 pounds. 

 A large number of young fruit was examined for live and dead 

 thrips. While this method did not give absolutely accurate results, 

 because of the number of thrips knocked off by the force of the 

 spray, it offered some means of comparison. Table I shows the 

 relative killing effect of the various washes: 



Taule I. — Killing effect of various .sprajjs on orange ihrips. 



Number of fruits 

 examined. 



Total 

 number 

 of thrips 

 counted. 



Number 



of thrips 



dead. 



Percent- 

 age of 

 thrips 

 dead. 



150 



200 



100 



Several hundred . 



Do 



Do 



Blackleaf 1-50 and distillate-oil emulsion 1 per cent. . 

 Blackleaf 1-60 and distillate-oil emulsion 1 per cent. . 

 Blackleaf 1-80 and distillate-oil emulsion 1 per cent. . 

 Blackleaf 1-85 and distillate-oil emulsion 1 per cent . 



Commercial lime sulphur 1-75 and blackleaf 1-50 



Commercial lime-sulphur 1-50 and blackleaf 1-100. . . 



129 



182 

 67 



126 

 170 

 64 



97.6 



93.4 



92.5 



75 



90 



95 



Experiments to Prevent Marking of the Fruit. 



Experiment No. I. — A block of 150 Washington Navel orange 

 trees was sprayed three times with distillate-oil emulsion and black- 

 leaf tobacco extract; the former at the strength of 2 per cent and 

 the latter in the proportions of 1 to 80 and 1 to 100 parts of spra3\ 

 The spraying was tried as a means of preventing the thrips from 

 curling the tender foliage and marking the young fruit. The first 

 application was made May 4, 1909, after most of the petals had fallen 



