232 EEPORT UPON COTTON INSECTS. 



structions of this kind could only be made to produce the maximum 

 results by offering a reward for every specimen captured before a certain 

 date, say Jane 1 ; a smaller reward might then be offered for each spec- 

 imen between that time and some subsequent date. We have no doubt 

 that were each planter to expend a small sum in this way greater returns 

 would be realized than could be obtained by the expenditure upon the 

 crop of a like sum any other way. And we are inclined to believe that 

 even in case where concerted action cannot be obtained good results 

 will follow individual efforts. For, although the summer and autumn 

 broods of moths migrate to great distances, there is reason to believe 

 that the hibernating individuals and those of the early broods do not do 

 so to any great extent. As evidence of this we cite the fact that con- 

 siderable time elapses between the appearance of the worms in those 

 localities which we have designated as centers of hibernation and in the 

 more northern parts of the cotton belt. 



DESTRUCTION OP LARVAE BY POISONS. 



Arsenic and its compounds. The only remedies which are now used to 

 any great extent are poisons applied to the plant 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 Cotton- Worm 

 Destroyer, 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 plants. With a 

 view to settling these points, I planned the experiments conducted by 

 Mr. Trelease, 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, which are given in 

 Appendix II (answers to question 7 ), I find tiiat 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 mineral with which we experimented, it is difficult to 

 apply a sufficient quantity to effectually destroy the worms without in- 

 juring the plants. We feel sure that the unfavorable results which have 

 followed in some instances from the use of Paris green have arisen from 

 one of the following causes, either an excessive use of the substance or 

 the use of an adulterated article, chiefly the latter. From the trials 

 which we have made, we are inclined to doubt that there is any danger 

 of scorching the cotton if pure Paris green be used in the usual way, 



