THE CAMPHOR THRIPS. 27 



On October 20, 1921, four lots of 10 eggs each, deposited the same 

 day, were fumigated with hydrocyanic-acid gas, two other lots being 

 kept as checks. The four lots were placed in an airtight fumiga- 

 torium with a capacity of 25 cubic feet and subjected for two hours to a 

 charge of gas produced from materials used at the strength of 1 ounce 

 of sodium cyanid, 2 ounces of sulphuric acid, and 4 ounces of water to 

 100 cubic feet of space. After fumigation the limbs containing the 

 eggs were removed and placed with the checks in the laboratory. The 

 following day no effects could be noted on the eggs. On October 27, or 

 seven days after treatment, the eggs were still unchanged and the check 

 eggs were hatching. On October 28 all the checks had hatched. The 

 experiment was discontinued October 31, since none of the fumigated 

 eggs had hatched. No change in their appearance could be seen, but 

 when broken they were found to contain a watery fluid, with no evi- 

 dence of an embryo. 



A similar experiment was performed on October 21, using 1 ounce 

 of sodium cyanid and an exposure of one hour. The results were 

 similar, no eggs having hatched up to October 31. 



On November 1 another lot of eggs were fumigated, using one-half 

 ounce of sodium cyanid to 100 cubic feet of space and an exposure of 

 one hour. The checks all hatched on November 9 and 10. None of 

 the treated eggs hatched, a few appearing shrunken and dried out after 

 several days, but most of them remaining unchanged in appearance 

 and containing a watery fluid. A final experiment was made on 

 November 1, using two lots of eggs of about 40 each, which were 

 fumigated for one hour at the rate of 1 ounce of sodium cyanid to 

 100 cubic feet of space. On November 7 a few of the eggs were 

 shrunken and collapsed. By November 12 all the checks had hatched 

 but none of the treated eggs hatched, nor did they contain any live 

 embryos. 



In all these experiments there was 100 per cent mortality of the 

 eggs. Not a single egg remained alive after the fumigation. Results 

 from the various dosages and exposures used did not differ appre- 

 ciably. A strength of one-half ounce of sodium cyanid killed the eggs 

 as well as stronger dosages. For commercial practice, however, it is 

 recommended that the trees be exposed for one hour in an airtight 

 fumigatorium to gas produced at a strength of 1 ounce of sodium 

 cyanid to 100 cubic feet of space. The experiments prove that 

 nursery stock can be entirely freed from the camphor thrips in all 

 stages by this treatment. 



Further experiments with living nursery stock showed that the 

 trees will stand this treatment without any serious damage. On cut 

 limbs the bark turned black after a few days and dried out sooner 

 than it normally would, but on living camphor trees which were 

 defoliated and well pruned back there was no apparent deleterious 

 effect. In fact some of them withstood a dosage of 2 ounces of 

 cyanid and an exposure of two hours. 



Fumigation of course would not be practicable on commercial 

 camphor plantations, nor would it be possible to use it on large 

 ornamental trees and hedges. It is recommended only for nursery 

 stock or small trees when removed from the ground for transplanting. 



