374 Journal of Agricultural Research voi.vi.no.io 



however, a female M. destructor oviposited in a stem containing nothing 

 but partially grown larvae. Upon dissection the egg was found sticking 

 to the stem underneath the leaf sheath, close to one of the larvae. It is 

 not yet known whether or not M. destructor can develop to maturity on 

 partially grown Hessian-fly lar^^ae. The egg stages of 96 specimens 

 placed on Hessian-fly lan-ae in glass slides varied from i }4 days in hot 

 July weather to 4 days in cool September weather. The larva emerges 

 from the egg by breaking through one end. After crawling around a 

 little the larvae reared in glass cells fastened themselves with their mandi- 

 bles to the outside of the host lar^'ae in order to feed. 



THE LARVA 



The full-grown larv^a of M. destructor (PI. LI I, fig. 4) is white with the 

 dingy brown contents of the alimentary tract visible through the integu- 

 ments. There are two pairs of slightly raised circular tubercles on the 

 front of the head near the top. The lower pair are slightly farther apart 

 than the upper pair and each bears a small conical projection, evidently 

 an antenna, varying from white to pale brown in color and about 0.02 

 mm. long. The median ventral surface of the head bears the round 

 suctorial mouth opening. The only mouth appendages distinguishable 

 are a pair of brown chitinous mandibles borne laterally and closing 

 together across the mouth with their tips overlapping (PI. LII, fig. 3). 

 The distal portion of the mandible is conical, tapering gradually to a 

 sharp point. The proximal end is suddenly enlarged, evidently to pro- 

 vide for muscle fastenings. One subdorsal and one sublateral row of 

 very short and inconspicuous setae on each side of the body are clearly 

 distinguishable in some specimens, extending the full length of the body, 

 one seta per segment in each row. On some specimens there appear to 

 be two ventral and two dorsal rows of scarcely discernible setae on the 

 first three body segments only. There are thirteen body segments be- 

 sides the head, the anal segment being divided into a dorsal and a ventral 

 lobe by a horizontal fold across the end. The dorsal lobe bears four 

 very short, fine setae in a row across the end, the setae composing the 

 row being usually in two lateial pairs. The ventral anal lobe bears only 

 two setae, one near each lateral end of the lobe. The length of the 

 full-grown larvae averages 2.5 mm., the largest diameter, 0.7 mm. 



Balsam mounts of all the material left behind in the little glass cells 

 by pupating lar\'se nearly always contained five pairs of mandibles. 

 Mounts of all the material left in the cell by full-grown larvae which had 

 ceased to feed, together with the mandibles dissected from such larvae, 

 also nearly always contained five pairs of mandibles. In every mount 

 the pairs varied uniformly in size from those resembling the ones borne 

 by. newly hatched larvae to those borne by full grown larvae. Mandi- 

 bles of newly hatched larv'ae were somewhat hooked. All the remain- 

 ing pairs were similar in shape, and corresponding pairs in all the mounts 



