PYRETHRUM AS USED AGAINST THE COTTON WORM. 1^)9 



owe the first accurate determinatioii of the destroying principle in Py- 

 rethrum. He wrote us as follows on this subject: 



I have had Milco's product in hand for some time, and have tried it on various bugs 

 both in pojvder and infusion. To understand the best manner of using it in each 

 case, it must be kept in mind: 



1. That the active substance is a volatile oil. 



2. That said oil, under the influence of air, not onjy volatilizes, but is also oxidized, 

 and thereby converted into an inert resin. 



It follows from 1 that the pyrethrum is at a disadvantage when used in the shape 

 of powder in the open air, especially when the wind blows; from 2 that it is of the 

 greatest importance that the substance should be fresh, or should have been kept 

 tightly packed, for the same reason that hops must be similarly treated. 



Hence I find that Milco's fresh powder is of greater efficacy than the best imported, 

 although some of the latter contains twice as much matter soluble in ether ; but the 

 extract from the **buhach" is a clear greenish oil, while that from imported powder, 

 and especially that from " Lyon's magnetic" — ground-up refuse, stems, &c., as I take 

 it — is dark and thickish, or almost dry and crumbly. 



The real nature of the effect of this volatile oil on insect life has not 

 yet been studied, and still remains obscure. Different species of 

 insects are differently affected by the powder, but since no other 

 animals are affected so far as we yet know in anything like the same 

 xiegree, it may be inferred that with insects those organs are affected 

 which are essentially characteristic of them, viz., those connected with 

 respiration. Some insects resist the action of the powder to quite a 

 marked degree, e. g.^ very hairy cateri^illars, and especially spiders of 

 all kinds; while others, especially all Hymenoptera, succumb most 

 readily. In no case are the insects killed instantaneously by Pyrethrum. 

 They are rendered perfectly helpless a few minutes after the applica- 

 tion, but do not die till some time afterward, the period varying from 

 several hours to two or even three days, according to the species. 

 Many insects that have been treated with Pyrethrum show signs of 

 intense pain, while in others the outward symptoms are much less 

 marked. 



The eff'ect of Pyrethrum on the Cotton Worm may be described as 

 folloT^s : The worm becomes uneasy in from 5 to 20 seconds after the 

 application, according to the amount of Pyrethrum applied, and, again, 

 according to the size of the worm. Yery shortly afterward it attempts 

 to bite off or to remove the particle or particles of the powder adhering 

 to its body, during which operation a greenish juice emanates from its 

 mouth. Its motions become more and more violent, until at last, within 

 from 4 to 10 minutes, the whole body is thrown into convulsions, the 

 worm having lost all control over itself. These convulsions continue 

 for manyjiours, the worm getting weaker and weaker until death ensues. 

 Small worms die in about 3 or 4 hours ) half-grown ones often not before 

 24 hours have elapsed. Full-grown worms are not easily affected, and 

 generally recover from the effects of even a pretty strong dose of Pyre- 

 thrum, while very young worms are mos'f readily affected even by a very 



