10 MASS. EXPERIMENT STATION BULLETIN 326 



Table 4. — Progressive Mortality of Common Red Spider on Potted 

 Carnation Plants Fumigated with Naphthalene 



Naphthalene vaporized at rate of \i ounce per 1,000 cubic feet each hour. 



Temperature 75° F. Relatively Humidity 85 percent . 



Waltham, Massachusetts. October 1935. 



Length of Time Total 



Fumigation Had Naphthalene 



Been in Progress Vaporized when- 



when Plants were Plants Were 



First Exposed Removed 



Percentage Mortality of Red 

 Spider After Exposures of — 



12 3 4 5 6 



Hour Hours Hours Hours Hours Hours 



At the beginning 



2 Hours 



3 Hours 



4 Hours 



Ounces 



1 

 1 

 1 



m 



i 

 i 

 m 



2 



14.19 



20.32 



32.78 



52.00 



83.89 



94.36 



16.38 



33.94 



55.20 



85.83 



19.39 



24.35 



84.68 



92.79 



16.66 



68.75 



85.08 



97.58 



Note: Percentage mortality of red spiders on plants not fumigated, 7.54. 



From this experiment it is apparent that normal fumigations under favorable 

 conditions do not give a reasonable control (85 percent dead) until the red 

 spiders have been exposed for 3 hours or longer to an atmosphere in which 

 at least % ounce of naphthalene per 1,000 cubic feet has been vaporized and 

 retained. 



Similar results are indicated in Figure 1 where the time required to build 

 up a calculated saturated atmosphere was decreased by increasing the rapidity 

 with which a normal effective dosage for a 6-hour exposure was vaporized. 

 In this experiment the vaporization of 3 ounces of naphthalene in 3 hours at 

 the rate of 1 ounce each hour killed 85 percent of the red spiders in 3 hours; 

 but at the rate of % ounce each hour for 3 hours followed by J4 ounce each 

 hour for 3 hours, an exposure of 4 hours was required to kill 85 percent of the 

 red spiders; and at the rate of 14 ounce each hour for 6 hours, a 5-hour ex- 

 posure was necessary to effect an equal mortality. 



Manipulation of the fumigant in this way is practical only in extremely 

 tight greenhouses under favorable conditions and with careful attention to 

 detail by experienced operators. 



