PREVENTING OVIPOSITION OF THE MOTH. 125 



corded here to show that this suggestion, which, theoretically, looks 

 l)hiusil)le enough, is practically beset with great difficulties. We quote 

 the following x)aragraph from Mr. Schwarz's report on experiments 

 made at Selma, Ala. : 



AVliilo experimenting witli decoctions and extracts of various plants, and knowing 

 that tlie matlis were ovipositing at tlie time, I tried the following three substances, 

 ■with a view to ascertain whether they rendered the plant sufficiently distasteful to 

 the moth to prevent her from ovipositing : 1. Infusion of Ailanthus leaves ; 2. in- 

 fusion of Walnut leaves ; 3 decoction of Hoarhound. The first I selected without any 

 special reason, being influenced only by the universal belief in its efficacy ; the second 

 because I knew by experience that it rendered the leaves distasteful to the worms; 

 the third, on account of its most powerful and unpleasant smell. 



The application of the three substances was made very easily, as the moths ovipos- 

 ited at this time (September 5) with preference on the leaves of the young shoots 

 arising from near the roots of the plants. Three small shoots, each on a different plant, 

 were then examined for eggs, and, after removing these with a knife, the infusions 

 were plentifully api^lied so that each leaf was fairly drenched from both sides. 

 (Selma, Ala., Sept. 5.) 



Examination on the 7th of September shows that none of my decoctions had the 

 slightest effect, the number of eggs laid on the three shoots being quite considerable, 

 and apparently not less than on other shoots not treated with any substance. There 

 Avas a heavy shower yesterday, but the leaves being sprinkled on both sides, the rain 

 could not have washed away every trace of the decoctions. 



Observations in the field seem to show that common road dust could 

 possibly be utilized to prevent oviposition of the moth. Mr. Stelle says, 

 in one of his letters from Calvert, Tex. : 



A much traveled road runs east and west through the field ; on the south side of it 

 the cotton is badly eaten by worms, while for 40 feet along the north side it does not 

 seem to have been much disturbed. I investigated for the cause of this exemption, 

 and found it to be the result of a south wind blowing the dust stirred up in the road 

 over the plants. It seemed to have at least retarded the work of both Boll and Cot- 

 ton Worms. 



Mr. Schwarz, while speaking of those spots in cotton fields which had . 

 escaped the general destruction by the worm in August, 1880, says : 



The outside row or rows of a field are very often exempt, sometimes even to a re- 

 markable degree, but by no means always. In some instances this immunity maybe 

 due to the direct influence of the road dust that thickly covers the leaves, but it oc- 

 curs also w^here there is no road, and consequently no road dust, and where, therefore, 

 another explanation is necessary. I fail to find any satisfactory explanation, unless, 

 perhaps, in such- cases the outside rows grow under conditions less favorable to the 

 plants, which thus have less attraction to the moth. 



Mr. Stelle himself noticed later the exemi)tion of the outside rows of 

 cotton fields. He writes in his diary, September 3, 1880: 



I have noticed in fields that the plants growing adjacent to open spaces, as along 

 roads, even though but little traveled, are more or less exempt from the working of the 

 worms. In the midst is about one-fourth of an acre in sweet potatoes, rank-growing 

 and clear of weeds. For about the width of two rows around the patch the cotton is 

 scarcely touched, while everywhere else it is completely trimmed. 



I have seen a similar case along the side of a patch of peas (Dolichos) where the 

 exempt rows were several hundred yards in length. 



Similar facts have often come under our notice and are quite com- 

 monly observed. 



