124 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 



Where baud -picking is followed, the pupse should Dot be crushed at 

 once, but placed in a barrel covered with a wire screen to admit of the 

 escape of the parasites, and at the same time to retain the moths and 

 cause them to perish. 



Immunity of Cotton under Trees. — The immunity of cotton 

 growing under single trees that are left standing in the field has long 

 been noticed and attributed to the protection and attraction afforded 

 to birds by such trees. We had adopted this view in the first edition 

 of this work, but the great regularity with which this phenomenon 

 occurs throughout the cotton belt, and several other circumstances 

 connected with it and presently to be mentioned, induced us to have the 

 subject re-examined. There is no doubt in our mind that this exemp- 

 tion of cotton is due to the direct influence of the tree on the plants 

 growing under it, and not to the birds and other enemies of the worm. 



Mr. J. P. Stelle, during his stay in Texas, conducted an experiment 

 which throws some light on the subject, and which he records in his 

 diary as follows : 



August 30, 188L It is tliou^rlit by all jDlanters that sliade protects cotton from the 

 work of the Cotton Worm, and it grows out of the fact that plants growing under trees 

 are more or less exempt. I have attributed the exemption to the work of birds ; but 

 the planters declare it to be shade. To settle the question I have to-day erected a 

 temporary shed over a number of plants by stretching an old tarpaulin above them, 

 on stakes in the center of a field. 



September 3. My temporary shade has proven a protection to the x^lants ; the worms 

 are not working under it to amount to much, though all around they have completely 

 stripped the cotton. 



Other observations show that cotton growing under a dense tree is 

 not only exempt from injury, but even not touched by the starving and 

 migrating worms. This fact alone indicates that the presence of 

 birds cannot be the true explanation. It has been further observed 

 that a small tree, or a dead one, even if it has many branches, has but 

 little protective influence, or none at all, on the plants growing under 

 it. That this influence cannot be entirely due to the shade alone ap- 

 pears more than probable, since it is -exerted on all sides of the tree. 

 Whatever the real cause may be that prevents the work of the worm 

 under such circumstances, it likewise affects the cotton injuriously, for 

 on poor soil such cotton remains very poor send small, while on rich soil 

 it grows rank, and consequently bears very few bolls or none at all. 

 There is no way of making any practical use of this influence of trees 

 on the work of the worm. 



PREVENTiNa OviPOSiTiON OP THE MoTH. — As a possible means of 

 prevention, the idea suggested itself to apply some substance to the 

 plants which, by its odor or otherwise, would drive off the moths, and 

 thus prevent oviposition. This idea opens, of course, a large field for 

 experimentation 5 but we confess that, for several reasons, we xlo not 

 hope for important results in this direction. The few experiments that 

 have been made are far from being encouraging, and are simply re- 



