162 MASS. EXPERIMENT STATION BULLETIN 179. 



Powdered suKur was burned at the rate of one-quarter of a pound per 

 1,000 cubic feet of space in a tight fumigating box containing a badly- 

 infested plant. After twelve hours' fumigation the plant was removed. 



Results. — The cucumber plant was severely injured and died. All 

 mites were killed, those quiescent failed to molt and the eggs did not 

 hatch. This experiment was repeated several times and the results 

 checked with those above. 



Fumigation with sulfur dioxide is an inexpensive and efficient method 

 of ridding an infested house of mites between crops. 



Painting Sulfur on Steam Pipes. — This is an old practice of florists in 

 combating the red spider, but has been proved beyond a doubt to be 

 absolutely worthless. 



(b) Hydrogen Sulfid (H.2S). 



Potassium sulfid (liver of sulfur) dissolved in water has been widely 

 recommended as an efficient spray for controlling red spiders, and it is 

 claimed that its efficiency depends upon the fact that it combines with 

 the carbon dioxide of the air, forming potassium carbonate and hydrogen 

 sul6d according to the following formula?: — 



Monosulfid: K2S + H2O + CO2 = K2CO3 + HzS. 

 Polysulfid: KjSs + H2O + CO2 = K2CO3 + H2S + 4S. 



As an insecticide it is claimed that this sulfid acts by virtue of its caustic 

 properties and the hydrogen sulfid given ofT by its decomposition, this 

 gas being for insects almost as poisonous as hydrocyanic acid gas. 



To determine whether hydrogen sulfid could be used with safety to 

 plants and still be effective in killing red spiders the following experiment 

 was performed: a plant infested with mites was placed for twelve hours 

 in a fumigating box containing a 1 per cent, atmosphere of hydrogen 

 sulfid. 



Results. ■ — The plant was severely injured and died, while the mites 

 and eggs were unaffected. 



(c) Carbon Bisulfid (CS2). 



Experiments using carbon bisulfid at the rate of 2 pounds per 1,000 

 cubic feet proved to be inefficient in controlling the mites even after a 

 twelve-hour fumigation. The plants in this case were not injured. Carbon 

 bisulfid at a higher rate would be too expensive to use in commercial 

 houses, and therefore further experiments were discontinued. 



(d) Benzene or Benzol (CgHg). 



Early in the experiments on the control of red spiders it was found 

 that benzene vapor had a very active effect upon the mites. However, 

 this proved to be only a temporary stupefication, and mites which had 



