28 BULLETIN 1225, U. S. DEPARTMENT OF AGRICULTURE. 



SUMMARY. 



The camphor thrips first appeared in 1912 as an enemy to the newly 

 developing camphor industry in Florida. At that time large acreages 

 of camphor trees were being planted to produce a commercial supply 

 of camphor gum. The tree was also being widely grown for its orna- 

 mental value, both individually and in hedges. The thrips appeared 

 in enormous numbers when the trees were cut back to obtain wood 

 for distillation, and also when ornamental hedges were pruned back 

 in conventional shapes. The injury is not confined to pruned trees, 

 but much more aggravated cases follow such treatment. 



The thrips collect in large numbers on the stubs of the cut limbs 

 and then attack the new shoots as soon as they appear. The buds 

 are also attacked in the spring and at other times when new growth 

 appears. By feeding on the buds and tender tips the insects cause 

 them to become blackened and die back. Feeding also takes place 

 along the limbs, with the result that the bark becomes blackened 

 and cracks. Later these injured areas become enlarged by the thrips 

 working down into the wood, even causing deformed limbs at times. 



The camphor thrips probably is of Oriental origin, and not native 

 to Florida/ as was originally supposed. The bay trees of the genus 

 Persea were believed for a time to be the native host of the pestj 

 but the thrips which lives on the bay trees has been definitely shown 

 to be a distinct species. Repeated efforts to rear and establish the 

 camphor thrips on bay, avocado, and other closely related trees were 

 unsuccessful. Its activities are confined entirely to camphor 

 trees. The insect now occurs in practically all parts of Florida as well 

 as in adjoining States where camphor trees grow. It reproduces 

 rapidly, the generations requiring about 20 days in summer and 40 

 days in winter. The adults lay an average of 463 eggs and often live 

 for several months. 



The most practical method of control is a changed system of 

 pruning the trees. Cutting the trees off at the surface of the ground 

 rather than dehorning or cutting away part of the limbs eliminates 

 most of the damage. This system removes all hibernating places 

 of the thrips as well as their source of food. The trees later sprout out 

 from the crown and the new growth resulting remains free from 

 infestation for several months. 



If done at the proper time, good control can be obtained by spraying 

 with the following solution: % pound of 40 per cent nicotine sulphate, 

 2 quarts of potash fish-oil soap, and 2 quarts of lime-sulphur solution 

 in 50 gallons of water. Since the thrips have the habit of hiding in the 

 cracks and lesions of the bark during cool or cloudy weather it is 

 recommended that spraying be done on a bright, sunshiny day. 

 The maximum number of thrips will then be found feeding on the 

 leaves and buds and other exposed places. This method of control 

 will be found practicable only where a few trees are being grown for 

 ornamental uses, since the cost would be prohibitive on a commercial 

 camphor farm. 



When it is desirable to cut back camphor hedges, a material such 

 as shellac applied to the cut ends will prevent their dying back and 

 will also prevent the thrips from ovipositing there. 



Infested nursery stock can be fumigated with sodium cyanid at 



