76 



eighth to one-half grown, or sometimes even much larger, so that a 

 correspondingly large or small portion of the kernels beneath is 

 consumed during later development. Experiments made in the labo- 

 ratory show that a boll worm ma}^ consume from 30 to 50 kernels of 

 corn during its entire life. Allowing 900 kernels to an average ear, 

 this would mean an injury of from 3 to 6 per cent. Often more than 

 one larva ma}^ mature in a single ear, and again the silk ma}^ suppl}^ 

 the greater part of the food. Taking into consideration, also, that the 

 apical portion of the ear, which is least valuable, is the first destroyed, 

 the injur}' to iield corn will probably not often exceed the estimate 

 given above, and will, of course, fall lower wheie the percentage of 

 infestation is less than 100. Although the eggs are laid in the fresh 

 silks, the larvee scarcely ever hatch in time to destroj^ the silks before 

 pollination has occurred, so that the fertilization of the infested ear is 

 not interfered with. 



DAMAGE TO COTTON. 



The extent of the injury caused b}^ a single larva to cotton bears 

 directly on many questions of bollworm control, and has been investi- 

 gated carefully b}^ a series of experiments and observations made upon 

 cotton growing in the laboratory garden at Paris. 



The first series relates to very young cotton, and was made during late 

 May and early «Tune. At this time the plants were from 7 inches to 1 foot 

 high. On Ma\^ 31 two quarter-grown larvae were placed on one of the 

 largest plants and covered b\^ a wire-screen cage. Both entered the 

 soil to pupate on the lOtli of June, leaving the plant almost completely 

 defoliated, after the fashion in which the cotton caterpillar injures the 

 plants later in the season. Although the plant was in bad condition 

 when the larvae left it, later in the summer it was practically as well 

 developed as its fellows in the immediate vicinity. This and other 

 plants similarl}^ treated had not yet formed an}^ squares. The other 

 plants treated gave, on the whole, about the same results as the one 

 described, though the average extent of injury was somewhat less. 



A second and more important series of observations was made during 

 the latter part of Jul}^ and the first half of August. The plants exper- 

 imented on were about two weeks earlier than the general planting, 

 and hence were at that time in the same stage as the field crop during 

 August, when the third generation of boll worms is most destructive: 

 that is, when full of squares, flowers, and bolls. Six of the more com- 

 plete records are given in the succeeding paragraphs: 



Experiment 1. — A newl}^ hatched larva placed on a plant 2^ feet high 

 July 13. By the 25th it had entered the soil, after destroying twelve 

 squares, one one-fourth grown boll, and one flower. 



Experiment '2. — Small larva placed on a plant 3 feet high on Julv 

 15. It entered the soil on the 27th, after destroying one square, one 

 small boll, and two large bolls. 



I 



