OBSTRUCTIONS TO DEVELOPMENT 1 25 



retreated before its advance, and is now more common 

 in the South. In New Mexico' a parasite lives on the 

 eggs and larvae. The eggs are laid on the potato 

 leaves, on which the j'oung "bugs" live, chewing 

 holes in or eating the whole of the leaf. The insecfls 

 are most adlive about blossoming-time, and do con- 

 siderable damage if left alone. 



Modes of Combattijig. — The leaf should be thoroughl)- 

 coated with a poison, generally an arsenical compound 

 being used. The poison should be applied as soon as 

 the " bugs " hatch, because the younger the " bugs " 

 the more easily they are destroyed. Various arsenical 

 compounds are used — as, Paris green, arsenate of lead, 

 and others. "Bugs" obje(5l to Bordeaux mixture, 

 hence in applying the poison it is found to be good 

 practice to apply Bordeaux mixture at the same time. 

 The whole of the plant should be covered, because if 

 badly sprayed the bugs live on the unsprayed foliage. 

 The standard application is ]{ to ^ pound of Paris 

 green to 50 gallons of mixture. Generally i pound of 

 Paris green is suflEicient per acre, and if it is desired to 

 apply more than 100 gallons, the proportion of Paris 

 green .should be varied accordingly. If desired, Paris 

 green may be applied in the dry form by means of a 

 powder gun, the Paris green being mixed with flour, 

 land plaster, etc., as desired. About 50 cents per acre 

 should cover the cost of one application. 



The Potato Worm,^ also known in the South as 

 the tobacco-leaf miner {Gelec/iia opcrculella, Zell.), is 

 estimated to destroy 25 per cent, of the potato crop 



' American Naturalist, 1899, pp. 927-29. New Mexico Bui. 33, pp. 47-51. 

 2 Cal. Bui. 135, pp. 5-29. 



