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MASS. EXPERIMENT STATION BULLETIN 326 



Interval Between Fumigations 



Frequently, three or four successive fumigations within 10 to 15 days are 

 required to give satisfactory control. When successive fumigations are 

 necessary, the interval between treatments should not be longer than one 

 week during which time the majority of the spiders will have hatched from 

 eggs not killed by previous fumigations. In Table 5 the results of fumigations 

 at intervals of one, two, and three days show a slight advantage where the 

 fumigations were made on successive days. However, the mortality after 

 two- and three-day intervals is high and the differences are insignificant. It 

 is,therefore, apparent that within a reasonable period successive fumigations 

 should be made when the weather conditions are most suitable rather than 

 at any predetermined intervals. 



Table 5. — Mortality of Common Red Spider after Fumigations with 

 Naphthalene at Intervals of 1, 2, and 3 Days Between Fumigations. 



Dosage 2 ounces per 1,000 cubic feet. 



Temperature 75°F. Relative Humidity 80 percent. 



Waltham, Massachusetts. March 1931. 



Mortality of Red Spiders, Percent 



Operation and Number of Stoves 



The uniform vaporization of naphthalene throughout the total period of 

 exposure is necessary for successful operation, and this is governed by the 

 amount of heat generated by the stove. In coal-oil stoves this depends on 

 the height of the flame. In general, the flame should be about one-third 

 high but the proper adjustment of the stove wicks for each dosage can be 

 determined only by trial. Therefore, it is recommended that when making 

 a 6-hour fumigation the total amount of naphthalene crystals for each stove 

 be divided into six equal parts and that one part be added each hour. When 

 the calculated hourly dose is weighed, its volume can be marked in a small 

 pan or cup which can then be used as a measure for all subsequent doses. 

 By adjusting the stove wicks to vaporize the hourly dosage during the first 

 hour, the rate of vaporization should be uniform during the remainder of the 

 fumigation. After several fumigations many operators learn by observation 

 the correct rate of vaporization and can safely apply the total pan dosage at 

 the beginning, but even then it is strongly advised that frequent examinations 

 be made in order to readjust any wicks which may have varied from the 

 proper position. 



