PTRETHRUM : INSECTS DESTROYABLE BY IT. 39 



could be made by the hogshead at a triflinij expense, and distributed from a cart 

 by means of a syring^e. The tea should be made with briskly boiling water, 

 covered over closely, to prevent evaporation, but not boiled, as that would, seri- 

 ously impair its strength. 



AVhile the simple mixture of the powder with water gives such Stafis- 

 fiictory results, it hardly seems worth while to look for any other 

 method of using the Pyrethrum, for nothing can surpass this in sim- 

 plicity. It is only necessary, if the fresh and unadulterated powder 

 can be obtained, to mix a half pound of it in a pail of water and apply 

 It in a fine spray over the young caterpillars, slags, etc., feeding upon 

 the leaves. The eflfects upon them are wonderful : they quickly show 

 its operation in writhing and falling to the ground, from which, if the 

 solution is of sufficient strength, they cannot regain the plants, al- 

 though in some cases, death may not ensue until the following day. If 

 any are found eventually to recover, the solution should be made of 

 greater strength. It must be applied directly upon the infesting in- 

 sects, as it only acts by contact, and does not have the permanent ef- 

 fect of the poisonous insecticides which are eaten with the leaves.* 



The Insects that may be destroyed by it. — Pyrethrum appears 

 to be a very valuable agent for the destruction of the troublesome cater- 

 pillars of the cabbage butterfly — Pieris rapce Linn. Its efficacy for this 

 purpose has been recently shown in some experiments by Prof. Cook 

 at the Michigan State Agricultural College. One part of the dry 

 powder mixed with forty parts of flour and dusted over the cabbages, 

 in the latter part of September, killed two-thirds of the caterpillars 

 and stupefied some others. A tablespoonful of the powder mixed with 

 a gallon of water and applied with a common sprinkling-pot to nine 

 cabbages, killed of the larvae present 17, stupefied 39, and left but 3 

 alive — the examination being made the following day. From the ex- 

 periments which were carefully conducted (see Americayi NaUiralist 

 for February, 1881, pp. 145-147) Prof. Cook draws these conclusions : 

 *• they show conclusively that this powder is fatal to the caterpillars, 

 and that, too, in very dilute liquid mixture — 1-200 of a pound to a 

 gallon of water. We have only to sprinkle it on the plants, though it 

 may be necessary to make more than one application to insure com- 

 plete success. The success was better with the liquid than with the 

 flour mixture and can be applied with greater speed and economy." 



Some squash-bugs — Anasa tristis De Geer, which had been kept in 

 a close tin box, in the clear powder for three days, were not killed by 

 it. The Colorado potato-beetle can be killed by dusting with the 

 powder, and the larvas are quite susceptible to it. 



I have found the powder ineffectual for killing the harlequin cab- 

 bage-bug — Murgantia histrionica (Hahn.): it only paralyzed them 



*For the peculiar effect of Pyrethrum upon the heart-beat of a caterpillar, see Americav, 

 JUaturalist, 1882, p. 1015. 



