THE CARROT RUST FLY 



25 



In these studies derris killed the flies with unusual speed and consistency, 

 especially as a dust. Corrosive sublimate, sodium fluosilicate, pyrethrum, sulfur, 

 and Bordeaux oil emulsion gave considerable protection to the carrot but did not 

 kill the flies quickly or consistently. Soot, naphthalene, and benzene compounds 

 were repellent but not particularly toxic to the flies. In these cages some of the 

 flies on the untreated carrots lived 8-13 days, and the average life of those on 

 plants with general insecticide treatments was about 7 days. However,~when the 

 plants were dusted with derris mixtures no flies lived longer than 2 days. 



Figure 3 



MORTALITY OF CARROT RUST FLIES IN 

 24 HOURS ON POTTED CARROTS DUSTED WITH 



DERRIS. VfALTHAM, MASS. 1926-1930. 



* \ 2 lb ^ 5 (> * 1 2 3 -* S (, 



NUMBER OF DAYS AFTER APPLICATION WHEN 

 FLIES WERE EXPOSED TO TREATMENT 

 it - I HOUR 



Another series of tests indicated that undiluted derris dust killed all the flies 

 in 24 hours when they were confined with the plants 4 days after the dust was 

 applied, but that it was only partially effective 5 and 6 days after application. 

 Derris-gypsum dusts containing 75 percent and 50 percent derris killed all the 

 flies 3 days after application, but a dust containing ii percent derris killed only 70 

 percent of the flies when they were exposed to it immediately, as is shown diagram- 

 matically in Figure 3. 



Seed Treatment with Calomel 



Coating the seed with mercury salts has given considerable control of root 

 maggots in onion, cabbage, and cauliflower, as reported by Glasgow (16). Field 

 experiments with carrot seed treated with calomel (mercurous chloride) were 

 made at Waltham from 1929 to 1937. The treatment was applied by placing 

 the seed with one-half its weight of calomel or calomel-clay mixture in a bottle 

 or can and thoroughly shaking until the seed was completely coated. On ordinary 



