June 5, 1916 Hessian-Fly Parasites 371 



The larvae reared in glass cells normally pass through five instars. 

 Nearly all mounts made of the material left behind by larvae which had 

 finished feeding showed a total of five pairs of larval mandibles, while in 

 the remaining mounts from two to four pairs were found which always 

 correspond in size and shape to some one pair in the complete series. 

 Five was the maximum number found in any one instance, and in cases 

 where less than five were present it appeared that some of the molts had 

 been lost in manipulation. Where five pairs of mandibles were found in a 

 single mount, the sizes increased fairly uniformly from the second molt 

 to the last. The mandibles and head shields of newly hatched larvae 

 appeared to be m.ore heavily chitinized than those of later instars, except 

 the last, and somewhat larger than those of the second instar. The man- 

 dibles of all instars are similar in shape. They articulate laterally with 

 the head and fold together across the mouth, the ends overlapping. They 

 are decidedly curved, taper to points, and are brown and chitinous. The 

 sharp distal portions of the mandibles enlarge suddenly into a compara- 

 tively broad base bearing a chitinous lobe on the ventral side. The fol- 

 lowing average measurements will show the relative sizes of molted man- 

 dibles. These measurements represent the distance in a straight line, 

 from the tip of the mandible to the shoulder, where the mandible suddenly 

 enlarges into the broad basal portion. 



Moit No. Length of mandible. 



I o. 016 mm. 



2 016 mm. 



3 024 mm. 



4. 032 mm. 



5 048 mm. 



The full-grown larva is grayish white, averaging about 3 mm. long and 

 0.9 mm. in diameter, with 13 body segments besides the head. There 

 are no tubercles on the head, but there is a row of four hairs evenly spaced 

 across the top. The front of the head bears a pair of hairs, one on each 

 side, just outside of each of which is a very short, white, conical projection, 

 apparently antennae. There is a short bristle near the base of each man- 

 dible. The mouth is chitinized along its upper edge, this brown, chiti- 

 nous rim extending around the bases of the mandibles and bearing six 

 toothlike lobes pointing downward along the portion of the edge betv/een 

 the mandibles (PI. LII, fig. i). A subdorsal and sublateral row of fine, 

 white hairs runs the full length of the body on each side, one hair per seg- 

 ment in each row. The first three body segments bear several additional 

 rows. What appears to be the anal segment is divided into a dorsal and 

 a ventral lobe by a transverse invagination across the end. The dorsal lobe 

 bears two pairs of short, fine hairs, one pair close together near each lateral 

 end of the lobe. The ventral lobe bears a short hair at each lateral end. 

 The body hairs are evidently tactile organs, since when any of them are 

 touched, the larva wriggles and bites viciously at the point of contact. 



