26 BULLETIN 1225, U. S. DEPARTMENT OF AGRICULTURE. 
was also considerable injury on the rows pruned in November and 
December. The least damage was noted on those trees pruned dur- 
ing the hot summer months. The thrips have a habit of congregat- 
ing in large numbers along the sides of the stubs near the cut ends. 
They also lay large numbers of eggs on the cut surfaces. Hence 
these cut limbs are soon killed and are unable to put out new growth. 
This experiment, like those previously recorded, showed that prun- 
ing the trees to the level of the ground results in much less injury 
from thrips and also produces a more vigorous growth then when the 
trees were pruned by the branch method. 
TREATMENT OF ORNAMENTAL HEDGES. 
When grown for ornamental hedges, it is often desirable to prune 
camphor trees frequently and thus keep the hedge in regular forma- 
tion. Since tins will result in injury from the pruning and also in 
subsequent injury by the thrips, some experiments were conducted 
on camphor hedges to determine whether they could be treated to 
prevent dying back and also to prevent much of the large infestation 
of thrips winch usually follows pruning. A row of trees averaging 
about 4 feet in height were cut 1 foot from the ground on December 
29. The cut ends of one-third of the row were treated with commer- 
cial or painter's shellac and one-third with concentrated lime-sulphur 
solution and nicotine sulphate containing 40 per cent nicotine, diluted 
1 to 200. The remaining one-third of the row was left without any 
treatment whatever, as a check. As was to be expected, the thrips 
soon deposited enormous numbers of eggs on the cut ends of the 
untreated trees, but no eggs were deposited on the treated trees. The 
trees treated with shellac did not die back at all and after a few 
months put forth new growth near the cut ends. The shellac pre- 
vented the cut ends from drying out and consequently there were no 
unsightly dead branches. The lime-sulphur solution and nicotine 
sulphate treatment also prevented the trees from dying back to a 
large extent, but the growth started a little nearer the ground. The 
untreated trees also put forth vigorous growth, but the shoots were 
very close to the ground and unsightly dead branches were present in 
great abundance. 
Therefore, if it is desirable to prune an ornamental hedge of camphor 
trees so that they will retain their beauty, it is advisable to treat all of 
the cut ends possible with some material that will seal them up and 
prevent their dying back and also prevent the thrips from ovipositing 
there. Shellac has proved to be the best material for this purpose. 
FUMIGATION. 
With the end in view of preventing the spread of camphor thrips on 
nursery stock and small camphor trees, some fumigation experiments 
were carried on to find a safe and effective method of treating the 
trees. Previous work along this line reported by Berger (10) and 
Newell (7) (9) showed that scrubbing and dipping the trees with 
soap, oils, and other insecticides is not entirely satisfactory. Many of 
the adults, larvae, and pupae can be destroyed in that way, but some 
of the eggs are so protected in the bark as to escape injury. The 
fumigation experiments were intended, therefore, to destroy the eggs 
in the bark lesions. 
