69 



B nekton (British Aphides, vol. i, p. 70) has the following to say with 

 regard to the effect of weather on this and other species of Aphides : 



Violent changes of temperature seem much to check the multiplication of the 

 Aphides. A Gold rain, or the outburst of a thunder storm, will often cause the almost 

 entire extermination of swarms, and wash them, never to return, from their native 

 plants. Nevertheless, the close and hot atmosphere before a thunder storm seems to 

 to be peculiarly suited to their propagation. At such times the winged forms occur 

 in great numbers and take flight on the gentle winds, which transport them many 

 miles to other feeding grounds, to become the foundresses of other colonies. 



The effect of the parasites on the Grain Lonse was simply astonishing, 

 while their numbers were myriads. Going to the fields of recently har- 

 vested grain, if one stood in a position to bring the newly made shocks 

 between himself and the setting sun, he could clearly observe the 

 swarms of minute Hymenopters arising therefrom and flying away. Be- 

 sides, the stubble-fields were overrun with lady beetles and their 

 larvaB. 



Nevertheless, there are good grounds for the belief that the heavy 

 showers during the latter part of June and early July, in the central 

 and northern portions of Indiana, washed many young from the heads 

 of the grain and destroyed them. Besides, either the severe thunder 

 and lightning which accompanied these storms or the rapidly matur- 

 ing grain, or both, perhaps, caused the winged adults to betake them- 

 selves to the oat-fields, where they would probably have caused further 

 damage had not their relentless foes, the Hyrnenopters, pursued them 

 and continued their work of destruction. 



It was a common sight early in July, in northern Indiana, to see 

 adults of the grain-lice attached singly to heads of oats, sometimes with 

 a few young clustered about them, assuming the form and color so in- 

 dicative of parasitism. In southern Indiana, late in June, the same 

 thing was observed on oats, and parasitized adults were also abundant 

 on the heads of blue-grass, even long distances from grain fields. 



In summing up the matter, it may be safely said that wet weather 

 will not, of itself, prevent an outbreak of the grain Aphis, or dispel it 

 after under full headway. It must be borne in mind, however, that cool 

 wet weather, during May and June, will enable grain plants to sustain 

 greater drafts on their vitality than will very dry and hot weather. It 

 is also probably true that a cool temperature during spring and early 

 summer is either directly or indirectly favorable to the development of 

 the grain Aphis. 



Eegarding the life history of the species under consideration we have 

 never found them in the fields at an earlier date than April 27. From 

 this time we have an unbroken record of their occurrence up to July 9, 

 when there is a break in their continuity of appearance until Septem- 

 ber 1, when full grown apterous females were found on leaves of early 

 sown wheat. From this latter date we again have an unbroken record 

 up to December 30. We have also observed the sexes pairing on No- 

 vember 11 and December 3. 



