ANTS, BEES, AND WASPS 153 



larval stages upon other insects. A very few, however, 

 develop at the expense of vegetable tissues. The Wheat 

 Jointworm, of the genus Isosoma, is the most notable ex- 

 ample of the latter. The adult of this is a small fly 

 which deposits its eggs in the wheat stem at or near a joint. 

 The egg hatches into a tiny footless larva, which absorbs 

 the sap of the plant, causing the tissue to harden and the 

 growth of the wheat to be injured. The larva finally ma- 

 tures into a pupa and again into an adult fly. When it is 

 present in large numbers, it may seriously injure the 

 wheat crop, but it is comparatively easily destroyed by any 

 procedure that causes the destruction of the stalks contain- 

 ing larvae or pupae. The burning of the wheat stubble is 

 one effective remedial measure. 



OBSERVATIONS FOR PUPILS 

 IMPORTED CURRANT WORM 



1 . In spring or summer examine the leaves of currant and gooseberry 

 bushes carefully for the eggs upon the under side of the midrib and 

 secondary veins. Do you suppose all the eggs on one leaf are deposited 

 by one sawfly? 



2. If you find any leaves with eggs upon them, place the leaf in a 

 vivarium with the stem inserted in a bottle of water. Watch for the 

 hatching of the larvae, and feed them fresh leaves from day to day. 



3. Look at the lower leaves on the currant bushes to find some with 

 round holes in them. Are there any currant worms at work on such 

 leaves ? 



4. Raise a few currant worms in a jelly glass or other vivarium. 

 Note the changes of color from time to time. Can you find the cast 

 skins after molting ? Do the caterpillars stop eating and rest before and 

 after molting ? Where does the skin split open before it is cast off ? 



5. Examine carefully the legs on a good-sized currant worm. Are 

 they all alike ? Which are more pointed ? How many legs in all ? 

 Watch the insect as it crawls, and notice how the legs are used. 



6. When the larvae spin their cocoons, notice the texture of these. 



