104 MANUAL OF VEGETABLE-GARDEN INSECTS 



upper side of an openin<i: leaf, where it establishes itself and 

 begins feeding. A depression soon appears on the leaf at this 

 point which gradually develops into a pocket-like outgrowth 

 on the underside opening by a narrow slit in the upper side. 

 Within this pocket-like gall, the plant-louse becomes mature 

 and gives birth to seventy-five to one hundred and seventy- 

 five young, all of which acquire wings and on escaping fly to 

 beets or other food plants, where they produce young which 

 descend to the roots. This migration from the Cottonwood 

 takes i)lace mostly in July. Beets become infested both from 

 lice living over in the ground on last year's crop or on weeds, 

 and by the migrants from the cottonwood. 



The only practicable measure so far suggested for the con- 

 trol of the sugar-beet root-louse can be employed only where 

 irrigation is practiced. It consists in giving the plants the 

 maximum quantity of water that they can stand, thus forcing 

 the growth and at the same time producing conditions unfavor- 

 able to the multiplication of the insects. 



Beets are also sometimes infested by another species of root- 

 louse, Tychea hrevicornis Hart. This peculiar plant-louse is 

 wingless, with the abdomen very large and without cornicles. 

 Corn, sorghum, salt-grass, pigweed, purslane, mustard, lettuce 

 and dock have been recorded as hosts of T. hrevicornis. 



A closely related species, determined as the European T. 

 phascoli Passerini, has been reported as feeding on the roots of 

 bean and clover. There is some doubt as to the determina- 

 tion of the species of plant-lice found on the roots of many of 

 our common weeds and vegetables. They are in great need of 

 further study. 



References 



Wash. Agr. Exp. Sta. Bull. 42. 1900. 

 Parker, Jour. Ecou. Ent., 7, pp. 136-141. 1914. 

 Parker, Jour. Agr. Research, 4, pp. 241-250. 1915. 

 Maxson, Jour. Econ. Ent., 9, pp. 500-505. 1916. 



