October, '16] maxson: notes on pemphigus bet^ 501 



end and about 8 feet apart. A board 1 x 12 inches formed the base of 

 the cages and this was sunk into the ground to a depth of 10 inches. 

 These cages were put in place May 8 at which time the young stem- 

 mothers on the cotton-woods were in the first and second instars. 

 Beet seed was planted in cage No. 1 and in the spaces between the 

 cages on this date. Seed was planted in cages Nos. 2 and 3, June 4 

 and 27, respectively. After the seed was planted in the cages they 

 were not opened until the migration of lice from the cottonwood trees 

 was practically over when the weeds were pulled and the beets irri- 

 gated. 



September 28 the beets in the cages and in the spaces between them 

 were dug and a careful examination made for root-lice. It was found 

 that the beets in cage No 1, the earliest planted one, were all infested. 

 Those in cage No. 2 were infested but to marked degree less than those 

 in cage No. 1. The beets in cage No. 3 were entirely free of lice. All 

 beets in the spaces between the cages were infested, also. 



Host Plants 



Our knowledge of the apterous forms of the various species of the 

 genus Pemphigus is so limited that it would hardly be safe to say that 

 all root forms of this genus represent any particular species. For this 

 reason in discussing the host plants it should be remembered that some 

 of them may not be hosts of P. hetcv since a determination of the ap- 

 terous lice is not possible. 



The perennial plants which have been found to be hosts of Pem- 

 phigus sp. are of especial interest because of the fact that they play a 

 double role in the life^cycle of these insects. The following perennials 

 were found to be. hosts of Pemyhigus sp.: Yarrow, Achillea sp.; wild 

 aster, .As^er muUiflora; Solidago sp. ; Rumex sp. ; Agropyron sp. ; and Poly- 

 gonum aviculare. 



Summer colonies were found on the roots of Chenopodium album, 

 garden beets, sugar beets, and Cydoloma atriplicijolium. Pemphigus 

 sp. have been reported on carrots and sweet clover as well as alfalfa; 

 however, the writer has never been able to verify these reports. A 

 very close examination of many alfalfa fields, while the alfalfa was 

 being plowed up, has never revealed a single Pemphigian on the roots. 

 Lice of this genus have been repeatedly taken on turnips in the south. 



Effects of Lice on Sugar Content and Yield of Sugar Beets 



From the standpoint of the sugar manufacturer this is a very vital 

 point. The reduction of the per cent of sugar in the beets not only 

 reduces the quantity of sugar which can be made from a given acreage 

 which means a smaller year's profit for the manufacturer but also 



4 



