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 
exjpense of the operation. 
SPRAYING. 
The only method of control which has given good results is spray- 
ing at high pressure with 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 sprays 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 2J per cent nicotine; and commercial lime-sulphur (33° 
Baume) in combination with the tobacco extract. All sprays were 
applied with a hand pump, maintaining a pressure 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 : 
Table I. — Killing effect of various sprays on orange thrips. 
Number of fruits 
examined. 
Formula. 
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 spray. 
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 
