THE OUTBREAK OF 1907. 31 



following day large numbers of Toxoptera were on the wing, always 

 moving north. In a field of oats, sown in February, the plants had 

 hitherto been very thrifty, but at this time in a great many of the 

 drill rows the plants were about dead for a space of 8 or 10 feet, and 

 in case of later sown fields the plants were all fast dying under the 

 attack. There was becoming gradually apparent a fact of consider- 

 able importance regarding the relative number of winged forrns in 

 the fields. In oats fields where the food was succulent and good it 

 was difficult to find a single pupa, while in older and less succulent 

 wheat, perhaps within a yard of the oats, pupae would form 75 or 80 

 per cent of the population of the blades. This was afterwards verified 

 repeatedly by observation and by actual counting; indeed, through- 

 out the entire spring this fact seemed to be substantiated. 



From March 31 to April 3 Mr. Ainslie carefully examined fields of 

 wheat and oats in the vicinity of Wellington, Kans. He found wheat 

 fields invariably evenly infested with Toxoptera though nowhere in 

 any great numbers. Many of these were winged adults, indicating* 

 that they were migrants, and the young about them clearly evidenced 

 a recent invasion. No dead areas were observed in the fields north 

 of Pond Creek, Okla., but between Kingfisher and this point the 

 circular dead spots were plainly in evidence. These dead areas, 

 (PL I, fig. 2), from their regularity in the field, plainly indicated the 

 rows of oats shocks of the fall previous and were clearly to be seen 

 where the oats had been shocked and allowed to stand through a period 

 of wet weather. This generally produced a vigorous growth of 

 volunteer oats when the shocks were finally stacked or removed, 

 and in this young grain the Toxoptera seem to have had an early 

 start. In some cases it was easily possible to observe these spots 

 all over a field, although the volunteer oats were rarely entirely 

 killed — perhaps only changed to a reddish color. The infestation 

 seemed to be more marked in the wheat in the vicinity of these spots, 

 and later the Toxoptera swarmed about these places. 



It may be noted that these observations of Mr. Ainslie in north- 

 western Arkansas, southern Kansas, and northern Oklahoma were 

 made upon the same dates as those of the junior author about Fort 

 Worth, Tex., and at Hobart in southern Oklahoma, thus covering 

 a latitude of nearly 400 miles. 



Mr. Ainslie returned to Kingfisher, Okla., April 3, and was joined 

 there by the junior author on the 8th of the same month, where a 

 number of experiments were carried out in the field, the results of 

 which are given in the proper place. By the 8th of the month para- 

 sitized Toxoptera was found excessively abundant in the fields, in 

 evidence of which a case was noted where a section of a leaf of wheat 

 1J inches in length carried 43 brown, parasitized individuals. Mr. 

 Ainslie left Kingfisher, Okla., for Wellington, Kans., on the following 



