POTATO INSECTS 



159 



Fig. 91. 



The common stalk-boivr, 

 larva (X U). 



middle of the third thoracic segment to the middle of the 

 fourth abdominal segment, dirty greenish gray with the white 

 dorsal stripe only present, the lateral stripes being broadly 

 interrupted. This caterpillar is distinguished from its near 

 relatives by having but one tubercle behind the spiracle on 

 the eighth abdominal segment ; 

 by lacking the large plates on 

 the second and third thoracic 

 segments and by the presence 

 of a pair of small plates on 

 the next to the last abdominal 

 segment. The full-grown caterpillar is slightly less than 1^ 

 inches in length and similar to the preceding stages except 

 that the stripes on the body gradually fade out into a dirty 

 greenish gray and finally disappear shortly before pupation 

 occurs (Fig. 91). The caterpillars reach maturity in August 

 and transform, usually in the burrow, into a brownish pupa f 



inch in length. The moths 

 emerge in September and 

 October and deposit their 

 eggs on the stalks of their 

 food plants. The pupal 

 period lasts about three 

 weeks. 



There are two varieties 

 of the moth. In the 

 typical form (P. niteJa), 

 the front wings are grayish 

 brown with a slight olive 

 tinge, lightly dusted with white. The usual outer line is 

 pale and bent inward about one fourth of the distance from 

 the front margin of the wing and then runs nearly straight 

 across the inner margin. The hind wings are slightly paler 

 in color except towards the margin and on the veins. In the 



Fig. 92. — Moth of the common stalk- 

 borer, variety P. nebris (X li). 



