October, '16] MAXSON: NOTES ON PEMPHIGUS BETjE , 503 



louse are leaving the galls on the leaves of the narrow-leaved cotton- 

 wood trees has a very marked effect on the number of lice on the beets 

 at harvest time. The writer has observed this fact in connection with 

 plots used in determining the relative effects of early and late irrigation 

 of beets. In all cases the plots irrigated during late June have been 

 much freer of root-lice at harvest than those irrigated the fore part of 

 July. 



Rotation of crops appear to have no effect upon the degree of in- 

 fection. In fact many times the first beet crop on alfalfa or grain 

 land is more seriously damaged by root-lice than any other. 



Natural Checks 



While in the galls the lice are preyed upon by a capsid and the 

 larvae of a syrphus fly. In the soil many lice are destroyed by the 

 fungous disease, Emptisa aphidis. The larva of the syrphus fly S. 

 pauxillus was taken feeding in a colony on a beet root. The flocculent 

 larvae of the little lady-beetle, Scymnus collaris, has been noted in 

 numbers among the root-lice in the field. The larvae of Hippodamia 

 convergens has been taken feeding upon the root-lice where the soil 

 was cracked about the beet. In California the larvae of Scymnus 

 appacuhis is known to feed upon the beet root-louse. 



Life-Cycle 



The writer has succeeded in following the life-cycle from the gall to 

 the gall in the insectary. Spring migrants of Pemphigus halsamiferce 

 Williams have been taken from the galls and colonized on sugar beets 

 which were grown from seed in sterilized soil and in muslin-covered 

 cages. The sexual forms have been secured on twigs of the narrow- 

 leafed Cottonwood tree, Popidus angustifolicc on the leaves of which 

 tree the galls appear. These twigs were placed in the cages. This 

 work was done in 1914. The sexuals mated normally and the females 

 produced eggs on the twigs mentioned. In the spring of 1915 the 

 eggs produced larvae which were placed on a seedling narrow-leaf Cot- 

 tonwood. These larvae located on the upper side of the leaves just 

 as the buds began to open and there formed the typical P. halsamiferce 

 galls. The migrants from these galls proved to be without doubt P. 

 halsamiferce. 



Synonomy 



In 1900 Professoi' Doane described the beet root-louse from the root 

 form in bulletin No. 42, of the Washington State Agricultural College, 

 giving it the name. Pemphigus hetce. In the late Thomas Albert Wil- 

 liams' "Aphididae of Nebraska" which was published in 1910 we have 

 the description of the spring forms and the galls. This form Mr. Wil- 



