Apr. 17. J9i6 Insect Injury to Cotton Seedlings 131 



determined. This was done in both the hotbed and the garden, and 

 the results were the same in both cases. I^eaves which were entire and 

 uninjured at nightfall would show large holes often occupying one-half 

 of their area on the following morning. Later observations have shown 

 practically entire leaves disappearing in the same manner during the 

 night. 



During the first few days when the injury was appearing in the hotbed 

 a number of examinations were made during the daytime in the attempt 

 to find some insect producing the injury, but not a single individual 

 which could be suspected of being the cause was noted. However, 

 on April 6, 50 square inches of the hotbed soil were examined to a depth 

 of 3 inches, and 12 cutwonns were found. If this was a fair sample 

 of the hotbed, the soil there certainly contained hundreds of the worms. 

 Eleven of these larvae were very small, while one was about an inch in 

 length. 



The presence of these larvae in the hotbed and the fact that they 

 were known to feed upon plant leaves made it seem quite possible that 

 they were responsible for more or less of the injury. Consequently 

 several examinations were made at night, and a number of cutworms 

 were found feeding on the leaves of the plants. At this time the same 

 injury was noted on clover and weed leaves in the hotbed. 



Several half-grown cutworm larvae collected on cotton in the garden 

 and hotbed were placed on the surface of the soil in a pot containing 

 a number of seedlings. This pot was placed in a screen cage and the 

 larvas attacked the seedlings at once. Plate XII, and Plate XIII, 

 figure I, show several seedlings injured by these larv^. 



STUDIES OF CLIMATIC FACTORS 



A number of tests were conducted to determine whether any of the 

 injury could be due to the exposure to low temperatures during the 

 night or to the hot sunlight in the morning before the plants had time 

 to become warm. In the first test a wooden frame was erected over a 

 cotton planting in the laboratory garden just prior to the sprouting of 

 the plants. This frame was 2}4 feet in height and was covered with 

 8-ounce duck. This cloth was placed over the frame at sundown each 

 day and allowed to remain until about 10 o'clock the following morning. 

 In this manner the radiation was reduced under this cover during the 

 night and the plants were protected from sudden exposure to the sun- 

 light in the early morning. A minimum thermometer was suspended 

 under the cover in the center of the bed about 1 5 inches from the ground 

 and another was suspended at the same height in the open garden a few 

 feet away. Records continued for a few nights showed only a slightly 

 higher temperature under the shelter, so the frame was lowered to within 

 i^ feet of the ground and the thermometers were lowered to 6 inches. 

 Following this the minimum temperatures under the cover usually ranged 

 a few degrees higher than in the open. 



