NAPHTHALENE AS A GREENHOUSE FUMIGANT 15 



Table 7. — Mortality of Red Spider at Different Humidity, Without 



Fumigant. 



Temperature 80° F. Exposures 6 hours each. 



Waltham, Massachusetts. April 1932. 



Relative Humidity 



Mortality op Red Spider, 

 Percent 



Percent 2 exposures 3 exposures 



90 54.28 59.13 



80 36.36 49.74 



70 29.36 44.44 



60 18.65 35.05 



In experimental fumigations of active red spiders in which the relative hu- 

 midity was controlled at 60, 70, 80, and 90 percent, the mortality of the spiders 

 again increased as the relative humidity was increased. As shown in Table 8, 

 this was especially significant when the dosage of naphthalene was 1 ounce or 

 \]/2 ounces per 1,000 cubic feet; but when the dosage was increased and the 

 mortality became correspondingly higher, the influence of the humidity de- 

 creased and was negligible. 



Table 8. — Relation of Relative Humidity to Effectiveness of 

 Naphthalene Fumigation Against Red Spiders. 



Dosage, 1 or \y 2 ounces per 1,000 cubic feet. 



Temperature 80° F. One exposure. 



Waltham, Massachusetts. April 1931. 



Mortality of Red Spider, 

 Relative Humidity, Percent Percent 



Dosage Dosage 



1 ounce l l /> ounce 



90 75.58 99.45 



80 70.17 99.20 



70 69.81 64.91 



60 56.37 42.85 



A similar effect on red spider eggs was noted in other experimental fumigations 

 with 13^ ounces of naphthalene per 1,000 cubic feet at 80° F. These fumiga- 

 tions, which killed all of the active red spiders, also killed the eggs at 90 per- 

 cent relative humidity but permitted 53 and 57 spiders (percentage not deter- 

 mined) to hatch from the eggs fumigated at 75 and 65 percent relative humidity. 

 Further evidence that red spider eggs are more resistant to naphthalene fu- 

 migation as the humidity is decreased is indicated by the general abun- 

 dance of red spider larvae after fumigation at the lower relative humidities, 

 summarized in Table 9. In these experiments the exact number of eggs and 

 larvae present before fumigation is not known, but the evident greater number 

 which survived the treatments at 60 and 70 percent relative humidity is 

 significant. 



