4 BULLETIN 186; U. S. DEPARTMENT OF AGKICULTUEE. 



here the seeds were examined carefully at several different times 

 to see whether all insects wore killed. The viability of the seeds 

 was then tested. 



Part of the germination tests recorded in tliis paper were made by 

 Mr. W. R. Lucas, of the Office of Foreign Seed and Plant Intro- 

 duction, but in most cases tests with treated and untreated seeds 

 were carried out by Mr. W. L. Goss, of the Seed Laboratory of the 

 Bureau of Plant Industry. 



In these experiments the duration of the exposure and the con- 

 centration of hydrocyanic acid were varied in order to determine 

 the minimum exposure and concentration of hydrocyanic acid which 

 would insure the death of all the infesting insects. It was also con- 

 sidered of interest to determine whether the seeds would be unin- 

 jured if exposed longer and with a higher concentration of the hydro- 

 cyanic acid than that necessary to kiU the insects. The duration of 

 the exposure and the amounts of sodium or potassium cyanid are 

 given in the description of the experiments. The 1-1-2 formula 

 was used for potassium cyanid and the 1-1^2 formula for sodiiun 

 cyanid. 



The iron fumigation chamber already described was used in most 

 of the experiments. In some of the preliminary work, however, 

 desiccators or bell jars were used instead. The essentials of the 

 method were the same in either case, and no description of these 

 pieces of apparatus seems necessary. 



EXPERIMENTS. 



The summarized results of these experiments are here given in 

 tabular form for comparison (Table I). 



Table I. — Summary of experiments in fumigating against insects. 



Material. 



Avocado: 

 26 seeds, 



Infested with — 



29 seeds. 



5 seeds. . 



20 seeds. 



Do... 



6 seeds.. 



10 seeds. 



One adult avocado 

 weevil {Hcilipus 

 lauri). 



Larvae of avocado wee- 

 vil (inclosed in a cot- 

 ton-plugged vial) 

 and broad - nosed 

 grain weevil {Caul- 

 optiilus latinasus). 



Larvie of Conotrache- 

 lus sp. and broad- 

 nosed grain weevil, 

 all stages. 



do 



Kind of cyanid 



and amount 



used. 



Sodium cyanid, 

 J gm., in des- 

 iccator. 



....do....,.,.. 



..do. 



Time 



of 

 expo- 

 sure. 



Result. 



.do. 



Hrs. 

 1 Insect dead. 



do I 6 



do 12 



Sodium cyanid, J 

 4 gms. 



All stages dead. 



.do. 

 .do. 

 .do. 



No insects alive 

 out of .50 exam- 

 ined of all stages, 



• iermiriationtest. 



22 out of 26 seeds germi- 

 nated. 



20 out of 29 seeds germi- 

 nated; 21 out of 25 

 germinated in con- 

 trol test. 



Seed cut up to deter- 

 mine mortality of in- 

 sects and not plant- 

 ed. 



No germination. 



Do. 

 All seeds germinated. 



Do. 



