INSECTS INJURIOUS TO POTATO, ETC. 223 



A single larva in a potato stalk is not sufficient to injure 

 it to any extent, although it must have a weakening effect, but 

 when many larvae occur destruction is complete. As many as 

 5 or 6 individuals may sometimes be found in a potato stalk. 



The beetles appear, in the vicinity of the District of Colum- 

 bia, in the latter portion of May, and the female deposits her 

 eggs singly in small slits about one-twelfth of an inch in length 

 made in the stalks of the insect's food plants, and occasionally 

 in the branches. In a week or ten days the larva hatches, 

 and feeds by making small channels which increase in size with 



Fig. \4-3.—Si§alphus curculionis- Parasite of potato stalk weevil. (After Riley) 



the growth of the insect downward toward the bases of the 

 stalks. The undermining of a stalk by the tunneling of several 

 larvae has the effect of impairing the vitality of the plant and 

 causing the leaves to wilt and die. Upon attaining full growth 

 the larva makes a cell of castings and woody fibers in which to 

 transform. The beetles of the new generation appear as early 

 as July 24. In northern localities development is slower, the 

 beetles seldom appearing before August and maturing as late 

 as September, and hibernation is always as a beetle. The 

 knowledge of this fact is of value in the control of the species, 

 as will be explained. 



