44 THE SPBIXG GRAIN-APHIS OB ' * GBEEN BUG. ' ' 



CHARACTER OF ATTACK. 



The actual effect upon the plant, whether chemical or physiological, 

 is not clearly understood. If a few Toxoptera be placed upon a per- 

 fectly healthy plant, in a few days the tissue in the immediate 

 vicinity of the aphidids will take on a yellowish tinge; if the aphidids 

 remain in one place for a considerable time and increase in numbers, 

 the whole plant gradually turns yellow and dies, the leaves changing 

 to reddish brown. 



When the original source of infestation arises from some one or 

 more points within a field, as described elsewhere in this paper, the 

 plants take on a yellowish color in small, almost circular areas, (PL 

 I, fig. 2) and as the Toxoptera increase in numbers the plants in the 

 center die, becoming reddish brown, and the aphidids work outward 

 in every direction from the center, gradually enlarging the spot until 

 it mav cover manv acres. When a field is infested from without by 

 migrating forms, the aphidids appear to spread evenly over the entire 

 field and the whole gradually turns yellow, and in cases of severe 

 outbreaks a whole field may die simultaneously. (See PI. I, fig. 1.) 

 These aphidids are essentially leaf-feeders, rarely if ever being found 

 injuring the heads or fruiting parts of the plant. 



Toxoptera appears to have a more strikingly disastrous effect upon 

 wheat or oats plants than any of the other common grain aphidids. 

 Seemingly when in no greater numbers than other species the plants 

 will succumb more quickly to the attack of Toxoptera. 



VIVIPAROUS DEVELOPMENT. 



Toxoptera gra rnin urn, as already shown, has been found to breed 

 over a wide range of country, and its behavior, under the varying 

 temperatures and climatic conditions prevailing over this vast terri- 

 tory, presents and opens up a broad field for investigation. 



IN THE SOUTH. 



In northern latitudes the normal manner of reproduction among 

 the Aphidids is both sexually and asexually. In southern latitudes 

 hese conditions, apparently, do not obtain, as here the normal means 

 of reproduction seems to be asexually, each generation being com- 

 posed entirely of viviparous females. 



South of about the thirty-fifth parallel, except in high altitudes, it 

 appears that Toxoptera breeds continuously throughout the year 

 without the appearance of the true sexes. April 6, 1906, Mr. George I. 

 Reeves, of this bureau, found the eggs of a plant-louse on wheat at 

 Xashville. Tenn., and Mr. Kelly found males (fig. 6), females, and 

 eggs of Toxoptera at Knoxville, Tenn.. in December, 1908. The 

 eggs found by Mr. Reeves may have been those of Toxoptera, but we 



