154 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 



SULPHUR. 



A machine for the application of the vapor of this mineral is described 

 in Chapter XIII ; but, so far as we can see, the machine has not been used 

 to any extent. Nor is it probable that sulphur vapor will destroy the 

 worms, when applied in the open air. 



RED LEAD. 



The following a€count of experiments with this substance is from Mr. 

 Schwarz's report : 



At the suggestion of Professor Barnard I made a few experiments witli red lead. 

 September 4 I dusted five worms slightly with the powder and placed them in a glass 

 jar together with a few fresh leaves. No effect visible after twenty-four or forty- 

 eight hours. Placed a few worms in a glass jar and fed them with leaves thickly 

 dusted with red lead. After eight hours no effect visible, but the worms did not seem 

 to have eaten of the leaves. After twenty-four hours three of the worms were dead, 

 two others showed the color peculiar to those poisoned by Paris green or Loudon 

 purple and died in the course of the day. 



September 19. — Red lead diluted with five parts of flour and the mixture thrown on 

 some plants which were fairly alive with young worms. Twenty-four hours after- 

 wards some poisoned worms were found ; thirty-six hours after application some more 

 dead worms, but in the mean time most of the mixture had been washed away by a 

 heavy rain, and the remaining worms were sufficient to defoliate the plants. I fully 

 believe, however, that this mixture would have been efficient to protect the plant if 

 the rain had not interfered. 



September 22. — Applied a mixture of one part red lead to ten of flour. Within 48 

 hours I noticed a few dead young worms, presumably killed by the poison, but most 

 of the worms were not affected, or, if so, not seriously affected. I had no further op- 

 portunity to experiment with this substance, but do not believe it can be advanta- 

 geously used as a substitute for Paris green or London purple, as it evidently does not act 

 so powerfully as either of the two. Further experiments are, however, necessary to 

 obtain a definite opinion regarding its value as an insecticide. Its price (so far as I un- 

 stood) is cheaper than Paris gi*feen, but more expensive than London purple. Its 

 value as an insecticide will, of course, depend also upon its influence on the plant, a cir- 

 cumstance to which I omitted to pay attention, though there was certainly no marked 

 injurious influence in my experiments. 



ROAD DUST AND ALLIED SUBSTANCES. 



The protection from the attacks of the worm and the prevention of 

 the ovipositing of the moth accomplished by thickly dusting the leaves 

 on both sides has already been mentioned on page 126. It still remains 

 here to speak of the property of road dust to drive off or kill the worms. 

 If a powerful jet of water is directed on the soil at the base of the plant 

 so as to splash the softened mud on the lower leaves, the worms on 

 them will be covered with the soil and many of the young ones are 

 unable to remove it. They fall to the ground and exhaust themselves 

 in frantic and fruitless efforts to clean themselves. The same result can 

 be accomplished by throwing dry dust on the plant during or shortly 

 after rainy weather, or after the plants have been thoroughly wetted 

 with a sprinkler. 



i^ot every kind of dust is suitable for this purpose, and for utilizing 



