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



The camphor thrips can be readily killed with a solution consisting 

 of -J pound of 40 per cent nicotine sulphate, 2 quarts of potash- 

 fishoil soap, and 2 quarts of lime-sulphur solution to 50 gallons of 

 water. This spray will kill all thrips which are hit by it. If it is 

 applied when the insects are present on the foliage in the greatest 

 abundance, it will reduce their numbers to a large extent. The 

 addition of the lime-sulphur solution and soap gives the spray com- 

 bination a greater penetrating power than the tobacco extract alone 

 and this seems to be an essential quality. 



On August 15, 1921, a row of camphor trees was sprayed with 

 this spray combination. The spray was most thoroughly applied 

 at 200 pounds pressure and the trees were drenched both inside and 

 out. The sun was shining brightly at the time and the temperature 

 was about 90° F. A large number of thrips were in the buds and 

 on the foliage, but of course many of them were also in the bark 

 lesions. On the following day, August 16, an examination showed 

 only 1 dead larva and no living thrips, either adults or larvae, on the 

 buds or new growth. On August 19, four days after the spraying 

 had been done, a very careful examination was made. No live 

 thrips were found on the leaves or buds, but 1 living adult and 2 

 living larvae were cut out of the limbs. Several dead adults were 

 also seen, some in cracks and lesions and others on the limbs. There 

 is no doubt that the spray killed all the adults and larvae that it 

 hit, but of course some of the insects were so thoroughly protected 

 in the bark lesions that they could not be reached. On August 

 22 a further examination showed that practically all of the thrips 

 in the buds had been killed. The examination showed only 1 live 

 adult and 1 first-stage larva. It should be stated, however, that a 

 heavy rain took place on August 21 which may have washed some 

 of the insects away. On unsprayed trees in adjoining rows not 

 more than 10 feet away many times more living thrips were present 

 than on the sprayed row. Prof. J. R. Watson (3) also has had 

 satisfactory results in killing the insects with this spray. 



Although it is generally admitted that the nicotine in the fore- 

 going combination spray is the killing agent, it appears that the 

 addition of lime-sulphur solution produces a much higher mortality. 

 On June 17 a row of camphor trees abundantly infested with camphor 

 thrips was thoroughly wet, both inside and outside, with a spray 

 containing 2 pounds of potash-fishoil soap and 1 pound of 40 per 

 cent nicotine sulphate to 50 gallons of water. The morning was 

 bright and the temperature high, and many thrips were feeding on 

 the buds and crawling over the branches. On examination, within 

 10 minutes after the spray had been applied, several of the thrips 

 seemed to be paralyzed. They were on their backs and kicking but 

 were still alive. The limbs were still wet and the thrips were held 

 in the liquid. At the expiration of an hour, when the spray had 

 dried, 7 dead adults were found, besides 5 living adults, 5 dead 

 larvae, and 10 living larvae. Some of the live ones were kicking 

 and it was doubtful if they would recover. After three hours, 

 however, many living adults and larvae were present on the trees. 

 At 1.30 in the afternoon, or five hours after the spraying, many liv- 

 ing adults and larvae were also found. There were not so many 

 adults as in the morning, but some of them may have crawled back 

 into the lesions in the bark. On the following day there appeared 



