116 TRANSACTIONS OF THE ILLINOIS 



trees heavily laden with apples, to which we gave no attention, there 

 were necessarily bred in these trees an abundance of codling moths 

 of the first brood, which, spreading to our experimental trees, 

 must have greatly increased the ratio of injury by the later broods. 



We have next to determine the time of the year at which 

 poisoning is the most effective; whether, in fact, it takes principal 

 effect upon the first brood or the later ones. A moment's reflection 

 will show that if only the first brood of the larva? was directly dim- 

 inished in a certain ratio, the second brood should show a siirilarly 

 diminished ratio, since these descend from the first; whereas, if l)oth 

 first and second broods are directly poisoned, then the ratio of dam- 

 age to the second brood should be greater than that to the first; or, 

 in other words, the percentage of benefit to the picked apples should 

 be greater than that to the fallen. Our data for the present season 

 do not apply to this question, since all the sprayings were made in 

 May and early in June while the apples were still very small; and it 

 is incredible that the poison should have remained upon the fruit 

 through all the vicissitudes of weather and time for the two months 

 and more, that elapsed before the appearance of the second brood of 

 larv*. The results of last year, however, when the spraying was 

 continued until September 3, give us important information. Refer- 

 ring to Diagram I it will be seen that the benefit to the picked apples, 

 instead of being greater than that to the fallen fruit, was last year 

 about twenty-seven per cent, less, so that certainly no appreciable 

 effect was produced by spraying during the life of the second brood. 

 The greater injury to the picked fruit is readily accounted for by 

 a circumstance to which I have already alluded, viz., that our 

 experimental trees were surrounded by others upon which no experi- 

 ment was tried, and were consec[uently subject to invasion by codling 

 moths of the second brood reared upon these unpoisoned trees. 



Not only do these experimental facts point to the inefficienc}^ 

 of Paris Grreen as against the later broods of the codling moth, 

 but it is plain that the result was what we must have expected 

 a jjrm-i. As the codling moth of all broods deposits the egg habit- 

 ually on the blossom end of the apple, the poison taking effect only 

 in case it reaches the surface of the apple between the calyx lobes, 

 it is evident that there is little probability of effectively poison- 

 ing the fruit when the apple is full grown and pendent upon its 

 stem. 



Furthermore! wish to emphasize especially the point that spra fl- 

 ing after the apples hare begun to hang downuards is unquestionably 

 dangerous, and should not be permitted under any circumstances if 

 the fruit is afterwards to be used. The results of the chemical 

 analysis reported to you last year show that even heavy wind and 

 violent rain are not sufficient to remove the poison from the fruit at 

 this season, and remembering that the stem end of the apple pre- 

 sents a large conical pit by which the poison could be received and 



