72 



The genus Torymus contains a number of species, which may be bred from 

 different galls. The females have the abdomen flattened ovate, and sometimes 

 prolonged to an acute point ; the abdomen of the males is very small, and the 

 insects are black. A not uncommon species is T. gigantea, which is bred from 

 the large globular galls produced on stems of golden-rod by a fly (Trypeta solid- 

 aginis), about the size of a house fly, with mottled wrings. 



The closel}^ allied genus Isosoma contains species which depart from the para- 

 sitic habits of the majority of the family, and become themselves noxious insects. 



Isosoma hordei (Fig. 40) is the well-known 

 Joint-worm of wheat and barley straw, 

 making gall-like swellings at the joints, 

 in which several cells may be found, each, 

 containing a little grub. 



The sub-family Pteromalinse contains, 

 amid a great complex of tribes and genera, 

 a correspondingly great number of species. 

 The typical genus, Pteromalus, alone con- 

 tains more than 30 species, of which some 

 are well-known parasites of butterflies. 

 P. puparum is recorded as bred from 

 eleven species of butterfly, and is a com- 

 mon destroyer of the chrysalids of the 

 cabbage white butterfly {Pieris rapce) and 

 of Vanessa antiopa. I have counted 

 more than 450 flies from one pupa of the 

 latter, and sometimes scarcely an unin- 

 fested chrysalid can be found. The species of Tetrastichus are also frequently 

 parasites of butterflies, while T. esurus (Fig. 42) has been bred from the cotton moth^ 

 The genus Trichogramma (which constitutes a sub-family) also has similar habits, 

 and T. minutum (Fig. 41) is a parasite of our 

 large Milkweed Butterfly (Danais archippus). 



Froctotrupid^. — This family has been but 

 meagrely investigated in Canada, although the 

 species are numerous, and often of interesting 

 structure. They are not so varied in coloring as 

 the Chalcidid^, to which they are closely related, 

 but are usually brown or black. Many of them 

 are wingless, living among low herbage and moss, 

 and some of the genera consist of species so 

 minute that they live and mature in the eggs of 



other insects. I have found clusters of moths' eggs from each of which, instead of 



a young caterpillar, has issued a perfect winged 

 fly (Tdeas orgyioe) Those of Scelio infest, I 

 believe, the eggs of grasshoppers or crickets. 



Pelecinid^. — This family is a very easy one 

 to study, as it contains only one species, Pelecinus 

 polyturator, the shape of which is so different 

 from all other hymenoptera that it can be quickly 

 recognized. This fine insect is of a glossy black, 

 with short wings, containing few veins. The male 

 has a club-shaped abdomen, but the female has hers 

 greatly elongated — about five times the length of 

 her head and thorax — her total length is about two inches. The females are 



