CHAPTER XVIII 

 HYMENOPTERA 



The Barberry Sawfly {Hylotoma herberidis) 



The brief account of this sawfly given by Graber (1890) indicates that 

 it differs in several particulars from the aculeate Hymenoptera as 

 described by various authors. The eggs, which are laid in small clumps 

 on the leaves of the barberry, are much elongated and distinctly convex 

 on the ventral side. The germ band is elongated, occupying nearly the 

 full length of the egg after two days' incubation. It lies on the ventral 

 side of the egg, its caudal end slightly curved into the yolk. At this time 

 the amnion and serosa are fully formed; the head lobes are conspicuous 

 and distinctly wider than the body, which as yet shows no segmentation. 

 A little later the caudal end of the germ band grows around the posterior 

 end of the egg for a short distance. In the three-day-old embryo, rudi- 

 ments of head and thoracic appendages appear, the stomodaeum is evi- 

 dent, and the antennae arise postorally in position. About a half day 

 later the antennae migrate forward, the body segmentation becomes 

 distinct, and the nerve cord is formed. 



At this time also the stomodaeum and proctodaeum are well devel- 

 oped, each with mid-gut epithelial rudiments at the blind end, these 

 rudiments each developing into two parallel ribbons. Meanwhile, the 

 embryo has shortened so that the anal opening is at the posterior pole of 

 the egg. Four days after egg deposition the two thoracic and the eight 

 abdominal spiracles are clearly in evidence as well as the abdominal 

 appendages, the homologues of the thoracic legs. Soon after this the 

 abdomen again begins to lengthen, this time curving ventrad, so that 

 shortly before hatching the posterior end of the abdomen reaches the 

 thorax. After four days the dorsal wall closes, without the rupture of 

 either amnion or serosa and wdth only a portion of the amnion taking part 

 in a provisional dorsal closure as in Diacrisia and some Coleoptera. Both 

 embryonic membranes persist until the time of hatching. 



A Hessian-fly Parasite (Platyg aster hiemalis) 



This proctotrupoid parasite of the Hessian fly deposits its eggs in the 

 eggs of the host. The early development of the parasite takes place in 

 the host egg and in the young host larva during the fall, the parasite 

 passing the winter within a well-developed host larva, which remains 

 on the wheat plant. 



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