I i ^,_,__. T __.„ 7 1 



48 THE SPBIXG GBAIX-APHIS OB GEEEX BUG. 



the temperature was above and precipitation below normal, during 

 this particular season, the effect was so evident that there is reason 

 to believe that under normal conditions these aphidids do not live in 

 fields directly exposed to the sun during the summer months. 



The table on pages 64-69 on daily reproduction, length of 

 reproductive period, and longevity show a decided decrease in all of 

 these for the summer months over those of spring and fall. The facts 

 upon which these figures were based could be secured only by pro- 

 tecting the aphidids from exposure to the hot summer sun. Aphidids 

 exposed without such protection were unable to live through the 

 season, though special care was taken to furnish them with a supply 

 of green food plants. 1 



Mr. Urbahns secured the following results by removing Toxoptera, 

 together with its green food plants, from a shaded position and sub- 

 jecting it to the temperature of loose, unshaded soil. 



August 18, with the soil temperature at 145° F. in the sun, 12 Toxoptera on a wheat 

 plant were exposed. 30 seconds; 5 fell to the ground dead, 7 remained on the plant 

 dead. 



Three adults and 4 young on a wheat plant were similarly exposed for 30 seconds, 

 after which time all were dead. 



One winged and 4 wingless adults on a wheat leaf were exposed for 30 seconds, 

 when they were found to be dead on the plant. 



Thirteen adult aphidids on wheat plants were exposed for 15 seconds, 5 fell to the 

 ground dead. After 30 seconds exposure the plant was removed to the shade; 6 more 

 were then dead on the plant and 2 were alive between the leaves. 



Soil temperature 118° F. (shaded by cloud). Nine aphidids on a wheat plant were 

 exposed for 30 seconds, 2 died, and 7 remained alive. 



A potted wheat plant bearing several hundred aphidids, the temperature being 114° 

 F. in the shade, was removed from the shade for 5 minutes. A large percentage of 

 the aphidids fell to the ground, gome survived, but many died. 



A potted wheat plant bearing several hundred aphidids was kept in the shade where 

 the maximum temperature was 114° F. Next morning many of the aphidids were 

 dead. 



When the soil temperature was 116° F. shaded by a thin cloud, 3 aphidids on a plant 

 were exposed for 60 seconds, 1 died, and 2 remained alive. 



August 19, the soil temperature being 128° F. in the sun, 12 aphidids on a young 

 plant were exposed for 30 seconds; 5 fell from the plant and died, while the other 7 

 were dead on the plant. 



When the soil temperature was 130° F. in the sun 12 aphidids on a young plant were 

 exposed for 20 seconds. All were then dead. 



When the soil temperature was 128° F. in the sun 11 aphidids on a plant were exposed 

 for 30 seconds; at the end of this time all were dead — 4 fell to the ground, and 7 

 remained on plant. 



At a soil temperature of 130° F. in the sun 8 aphidids on a plant were exposed for 15 

 seconds; all were then dead — 3 fell to the ground, and 5 remained on the plant. 



The results of these experiments prove that Toxoptera can not 

 survive the summer in the open fields in sections of the country 

 where the pest commits its most serious ravages with the greatest 



1 Mr. J. T. Monell suggests that this may be due as much or more to the hot, dry air as to the direct 

 rays of the sun. 



