REPOET OF THE ENTOMOLOGIST. 



315 



worms wore killed on it. The poison was as thickly applied on 9 as on 10, yet, despite 

 the double quantity of poison used, it was injured very little. The caterpillars were 

 killed. Vei-y little poison remained on sections 1, 2, and 3, of August 22, yet in a very 

 few places there was enough to kill the worms that wero then appearing in large mam- 

 hers on it. None remained on section 4, the foliage of which was, for the most part, 

 eaten up. 



September 7, the poison was found adhering finely to sections 5 and 6, and the 

 cotton was not at all badly scorched. There were very few worms on it. No trace 

 of the poison on section 7 could be found, but there were no atohus on it, and it was 

 not materially injiu'ed by scorching. Not very much remained on section 8, but there 

 were few caterpillars to "be found. The eottoii was uninjnred. The poison adhered in 

 quantity to 9 and 10, where the worms were all dead. Section 9 was slightly scorched, 

 section 'lO badly. The unpoisoned section before mentioned was covered with cater- 

 pillars, its foliage being entirely gone. 



September 9, about midday, when the sun was shining brightly, I applied poisons 

 to three sections to test the resistance of different substances to the action of the 

 weather. The quantitj- and quality of the poison being unimportant, I shall give 

 only the jiroportions of the substances used to dilute it. 



September 14, 1 noted that my sections up to No. 11 were about as before the rain. 

 Of 11, 12, and 13, all were more or less removed, and strangely enough the last, con- 

 taining the, smallest quantity of flour, had resisted the rain better than either of the 

 others. None of these stood it as well as most of the earlier sections which had already 

 been exposed to numerous rains. Owing to my departure from the field at this time 

 these latter experiments are exceedingly unsatisfactory, and I hesitate to base a very 

 pronounced opinion on them, but think that they go to demonstrate that plaster, unless 

 accompanied by a large quantity of flour, will not do to apply poisons with unless it is 

 absolutely certain that no rain will fall till they shall have time to kill the caterpil- 

 lars they are intended to destroy. 



Arsenic and Us compounds. — The only remedies ^vhic]l are now used to 

 any gieat extent are poisons applied to the x)lant for the destruction of 

 the larvae, and, almost "without exception, these poisons are either 

 arsenic or some compound of that mineral. The compounds of arsenic 

 used to the greatest extent are Paris green, Texas Cottou-Worm De- 

 stroyer, and, during the present season, London purple. 



Very great difference of opinion exists among planters with regard to 

 the relative value of these substances. This difference of opinion is not 

 only as to their relative efficacy as insecticides, but also as to their effect 

 upon the plants. Thus, although Paris green costs from six to ten times 

 as much as white arsenic, many planters prefer to use the former simply 

 because there is less danger of injuring the cotton i)lants. With a view 

 to settling these points I planned the experiments conducted by Mr. Tre- 

 lease, a report of which has just been given, and on going over carefully 

 the testimony of planters which I collected while in the field last year, 

 and the answers of our correspondents, I find that the experience of the 

 majority confirms the results of these experiments in indicating that 

 Paris green is the most desirable insecticide. It seems to act more 

 speedily than the other poisons, and, if used carefully, no appreciable 

 injury will result to the plants ; whereas, with arsenic and the other 

 compounds of this miaeral with which we experimented, it is difficult to 



