HYMENOPTERA 343 



plants, upon which they feed (Fig. 579). The larvae of some species are 

 leaf -miners ; some make galls on stems and leaves of plants. Among 

 the species that have attracted attention on account of their economic 

 importance are the following. 



The imported currant-worm, Pteromdea ribesi. — This is the com- 

 monest and best-known of the garden pests. The adult sawflies appear 

 early in the spring and the females lay their eggs in rows along the prin- 

 cipal veins on the underside of the leaves of currants and gooseberries. 

 They hatch in a week or ten days; and the larvae begin at once to feed 

 upon the leaves. The larvae are at first whitish, as they increase in size 

 the color changes to green; after the first molt the body becomes covered 

 with many black spots and the head is black; at the last molt they lose 

 their black spots and assume a uniform green color tinged with yellow 

 at the ends. When full-grown the larvae descend to the ground and spin 

 their cocoons, either just below the surface of the ground or beneath 

 rubbish; sometimes the cocoons are attached to the stems or leaves some 

 distance from the ground. A second generation of the sawflies appears 

 late in June or early in July; and sometimes a third generation is de- 

 veloped. 



The pear-slug, Caliroa cerasi. — This is a well-known pest of pear, 

 cherry, and plum. It causes the leaves of the infested tree to turn brown. 

 When such leaves are examined it is found that the injury is due to small, 

 slimy, slug-like larvae, which have eaten off the upper surface of the 

 leaves, leaving the skeleton of veins and the lower epidermis to turn 

 brown, wither and fall; sometimes trees are entirely defoliated in this 

 way by midsummer. When full-grown the larvae descend and burrow 

 into the ground a short distance, where each constructs an earthen cell 

 in which it transforms. A second generation of the sawflies appear and 

 lay their eggs about three weeks later. 



The rose-slug, Cladius isbmerus. — Often in the summer our rose- 

 gardens look as if fire had swept over them, so scorched and brown are 

 the leaves. The cause of this apparent conflagration is a transparent 

 jelly-like slug, greenish above and yellowish below, which eats the upper 

 surface of the leaves, leaving patches of the lower surface and the veins. 

 These slugs usually feed by night and remain hidden on the lower surface 

 of the leaves by day. When ready to pupate they crawl down or drop to 

 the ground and burrow beneath the surface; here each makes a little 

 cell and then transforms. The adult fly is shining black with smoky 

 wings and with the fore and middle legs grayish or dirty-white. The fe- 

 male is about \ of an inch in length. There are two broods a year, one 

 in June and one in August. The last brood passes the winter in the 

 ground. 



Suborder IDIOGASTRA * 



The Oryssids 



This suborder, includes a single small family of rare insects, the Orys- 

 sidae, which formerly was included in the suborder Chalastogastra. 



The suborder Idiogastra stands intermediate between the other two 



* Idiogastra: idio (idios), distinct; gastros (yoarTpos), the belly. 



