93 
[| l! 
[) ■ 
ft 
ngle season during which this work has been under my charge, 
it the conclusions already reached have a definite and appreciable 
due, which will probably make them welcome as a contribution to 
le subject. 
[ t HOT WATER. 
One of the applications most frequently advised is that of hot 
ater at a temperature sufficient to destroy the worms, but too low 
»injure seriously the plants infested. A series of experiments upon 
le subject, made by Mr. Coquillett, of McHenry county, are de- 
i ;nbed in the last report of my predecessor, I)r. Thomas, but as 
ley were made at a time and place when the cabbage worm itself 
as not to be had, the conclusions arrived at are still open to ques- 
on. As far as the species of caterpillars and plants experimented 
jDon are concerned, Mr. Coquillett’s experiments seem quite conclu- 
ve, but as various species differ greatly in their power to resist 
jurious conditions, the inference from the species used by him to 
te cabbage worm itself is not strictly warranted. For the purpose 
testing the exact effect of water of different degrees of temper- 
/mre upon the worms in the open air, and the cabbage plants 
dacked by them, I sent an assistant, early in September, into 
le field with an oil stove and a sprinkler, with instructions to 
st the matter thoroughly. The water was heated to a given tem- 
hrature, as indicated by a good thermometer, and applied imrne- 
ately to the infested plants. At 180° F., no effect whatever was 
roduced upon either plants or insects. At 140° the worms were 
ot injured, although they were apparently a little stupefied at first, 
id no perceptible effect was produced upon the plants.* At 158° 
[>e worms were nearly all killed, but the cabbage plants themselves 
pre also badly injured, the leaves, wherever the water struck, being 
trboiled, and subsequently withering. At 160° the same effect was, 
course, produced, but was still more marked. The cabbages at 
pis time were well headed out, many of the worms were full-grown, 
lid the others of various sizes from a half inch upwards. These 
1 :periments go to show that the worms are fully as hardy as the 
ibbages. 
j POWDERED PYRETHRUM. 
r The general efficiency of pyrethrum as an insecticide has been so 
illy attested, and its use for the protection of cabbages recom- 
ended upon so high authority, that the experiments were under- 
ken only for the purpose of exactly defining the conditions under 
nich it could be most successly applied. The powder was obtained 
pecially for this, experiment from Messrs. Lehn & Fink, of New 
irk, by whom it was said to have been recently imported from 
□rope. The powder was mixed for the first experiment with ten 
ri,rts of flour, and left to stand one night before being used. Four 
;arly full-grown worms were selected and brought to the labora¬ 
ry, where they could be carefully observed. The diluted pyrethrum 
,is applied thoroughly with a powder-gun, and in ten minutes the 
irms all exhibited their uneasiness by quick, jerking motions. In 
teen minutes, they were crawling slowly about and writhing as if 
| * An experiment, made later, with water at 145°, was equally unsatisfactory. The 
ibages were considerably wilted, and only about one-third of the worms were hurt. 
