ANNUAL REPORT, 1936 59 



A summary of these records follows: 



Average Number of Mealybug Eggs Eaten per Day 



Temperature Number Average ■ 



(Fahr.) of Larvae Length of Life Total 1st to 21st to 41st Day to 



Days Life 20th Day 40th Day to Pupation 



60° 6 28.83 2.36 1.90 3.39 — * 



70° 5 59.40 23.55 9.08 30.39 31.41 



80° 6 53.50 24.92 11.55 35.50 27.84 



♦None lived over 40 days. 



Naphthalene and Similar Compounds as Greenhouse Fumigants. 



(W. D. Whitcomb, Waltham.) The greater part of the experimental work in 

 1936 was done with some of the commercial fumigants now available which 

 have a naphthalene or benzene base. 



These fumigants do not recrystallize at the lower greenhouse temperatures 

 as does naphthalene and consequently can be used at any temperature suitable 

 for growing plants. It was found, however, that it was necessary to maintain 

 temperatures above 70° F. in order to obtain a satisfactory kill of the red spider 

 mite, and that a greater mortality resulted when the relative humidity was 

 75 percent or higher. These facts were brought out by fumigations with one 

 of the commercial materials at a dosage of y 2 ounce per 1,000 cubic feet for 6 

 hours. 



Mortality of Red Spiders, 

 Percent 



Temperature Relative Humidity 



Percent 1st 2nd 



Fumigation Fumigation 



85° F. (high) 75 (high normal) 98.10 100.00 



75° F. (high normal) 75 (high normal) 78.99 100.00 



75° F. (high normal) 55 (low) 59.68 94.72 



60° F. (low) 75 (high normal) 22.11 66.38 



Some of these commercial materials have undergone considerable experi- 

 menting in the past year, generally to correct a tendency toward bleaching of 

 pink flowers, especially carnations. The changes have generally been made by 

 sacrificing some of the effectiveness against red spider. Comparative fumiga- 

 tions at a dosage of y 2 ounce per 1000 cubic feet for 6 hours under approximately 

 uniform temperature and relative humidity resulted as follows: 



Material Sample - 



Mortality of Red Spider, 

 Percent 



One Two 



fumigation fumigations 



1 81.95 100.00 



2 78.99 100.00 



3 14.1 89.65 



4 56.41 98.02 



Commercial B. 



Commercial C. 



Experimental fumigations with these materials indicate that under reason- 

 ably normal conditions they should give very satisfactory control of the red 

 spider mite, especially on carnations. 



