9 



Experiment No. 8. — This experiment is introduced as a test of 

 No. 7. 



May 1 1.- -Two aphides are taken from a plant which has been 

 treated with yeast. One is dead when found, the other is killed ; 

 both are placed as in No. 7. No mycelium or fungoid growth of 

 any kind is developed in this experiment. 



Experiment No. 9. — This experiment was introduced for the 

 same purpose as No. 8. 



May II. — 5.30 P. M. Three living aphides are taken from a 

 plant not treated with yeast, and killed and placed as in No. 7. 



May 13. — The room has been quite cool and no mycelium has 

 appeared. 



May 15. — On one of the aphides a few fruits of a mold can be 

 discerned. None can be seen on the other two. 



This experiment seems to show that the mold developed in 

 experiment No. 7 on the body of the aphis which had died, has 

 no connection with the fact that the plant from which the dead 

 aphis was taken, had been treated with yeast. 



The result of these experiments, as a whole, as also many 

 others not here recorded which have a more or less direct bear- 

 ing upon the subject under .consideration, indicate plainly that 

 yeast cannot be regarded as a reliable remedy against such insects 

 as commonly affect plants cultivated in greenhouses, rooms and 

 parlors. Moreover, it is more than probable that the yeast would 

 injure many kinds of plants, especially those with delicate foliage 

 by spotting and soiling the leaves, and inducing fungoid growths 

 upon the jars or soil in which the plants are grown. Indeed, in 

 most greenhouses at the present time, it is not so much a ques- 

 tion of keeping down injurious insects, as it is the suppression of 

 molds and mildews of various kinds. The verbena rust only 

 need be named as an illustration of this point. 



Nearly all recorded experiments with the yeast fungus as an 

 insecticide, have been attended only by negative results. Among 

 these may be mentioned those of Prof. J, H. Comstock, of the 

 Department of Agriculture, who fed caterpillars in breeding 

 cages with leaves wet with dilute yeast. They seemed to thrive 

 as well as others not thus fed. 



Mr. Wm. Trelease tried last August a number of experiments 



with yeast upon the cotton-worm, in the vicinity of Selma, Ala.^ 



These experiments were varied and carefully conducted. In 



' " Report upon Cotton Insects." J. H. Comstock, Dept. of Agr. Washington, 

 1879- 



