38 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



Spiracle oval, inconspicuous, brown ; that of segment XI larger, somewhat 

 obliqued, and farther dorsad. The crotchets of the legs are variable in number, 

 often unsymmetrical, and generally arranged as follows : 



For the first four prologs, the crotchets vary from 11 to 18 in number ; for the 

 anal proleg they vary from 8 to 0. There are generally more present than in 

 Sanninoidea exitiosa (see fig. 10, c). 



As compai-ed technically with the full-grown larva of the peach borer, the 

 latter is 34 mm. long, G mm. in greatest width, with the width of the head 

 at least 3 mm. The head of /S*. exitios^a is slightly darker in color, with a dis- 

 tinct, though variable, subtriangular ])ale area on each epicranial lobe, where 

 they join below the vertical triangle ; the mandible is relatively more robust, 

 darker at the teeth, four of the latter distinct, the second tooth longest and more 

 slender, the outer next in length, the third one-third shorter than the second, 

 and obtusely rounded, the fourth a distinct tooth, but abruptly shorter, approach- 

 ing the fifth, which is a mei'e serration ; the two mandibular setjie are larger. 

 The lateriil margins of the clypeus are straight, each one changing angle at its 

 basal third, making the clypeus shaped like A , instead of triangular ; the basal 

 corners of it are truncate. The parclypeal pieces are generally straight, but 

 curving basally to follow the margins of the clypeus ; they are uniform in width. 

 The first two ocelli and the sixth are practically pigmentless. The shields are 

 darker yellowish. The arrangement of the tubercles is the same, but they are 

 relatively larger, as are also the accessory warts and the seta?. There is a less 

 number of crotchets in the prolegs, ranging from 8 to IG, and in the anal proleg 

 from 5 to 8. 



Though these technical differences exist, they can not be recognized 

 in all points without considerable study, and an examination of a 

 series of larvae. The most conspicuous difference is the greater size 

 of the larva of Sanninoidea exitiosa and its different aspect. 



During the course of its groAvth the larva molts several times, each 

 casting of the skin marking the end of a separate period of larval 

 development called an instar. There is no direct evidence by rearing 

 to show how many of these instars there are. but it has been shown 

 that the heads of lepidopterous larva? are of certain limited sizes in 

 each instar, and therefore by measurements of a large series of the 

 heads of these larvas the conclusion is reached that there are six, as 

 shown in Table I. The larva molts five times. The length of the 

 separate instars has not been determined, but Mr. Quaintance records 

 a little over seven months as the length of the larval stage for an 

 individual reared on jjeach out of doors, from September to the fol- 

 lowing April, in the latitude of Washington, D. C. 



