INSECTS INFESTING THE SWEET POTATO 



i239 



quently branching as in some other species. Before changing to 

 pupa it removes the faeces from its fork. The pupa (b) is also 

 green, with a black ring around the base of the first abdominal 

 pair of spiracles. 



The Two-striped Sweet-potato Beetle (Cassida bivittata Say.). 

 — In 1869 this was stated to be the most common of the tortoise 

 beetles occurring on sweet potato seeming to be confined to that 



Fig. 154.— Two-striped sweet-potato beetle. 1, Larvas at work on leaves; 2, larva; 

 3 pupa; 4. beetle. J. Natural size; 2, J, 4, enlarged. (From Riley) 



plant. From the District of Columbia northward, where the 

 writer has observed it, it is much less abundant than the two 

 preceding, hence it is of less importance economically. The 

 beetle (fig. 154, 4) is yellow and has two black stripes on the 

 elytra, whence the common name. The larva (2) is dirty 

 whitish or yellowish, showing a rather indistinct line along the 

 back. From similar larvse on sweet potato it can be known from 

 the fact that it does not use its fork for 

 carrying excrement, but only as a repository 

 for cast skins. This fork is usually elevated at 

 an angle of about 45°, which suggests the idea of 

 a handle. 



The Black-legged Tortoise Beetle (Cassida 

 ni gripes 01.). — From other sweet-potato tortoise 

 beetles this species (figs. 155, 156) may be dis- 

 tinguished by its larger size. It measures nearly 

 one-third of an inch. Like the golden tortoise 

 beetle, it is reddish except when in bright sunshine, and has the 

 same power of assuming a golden hue, apparently at will. Its 



Fig. 15 5. -Black- 

 legged tortoise 

 beetle. (After 

 Riley.) 



