ORDER DIPTERA 



257 



length of it. When the larvae reach maturity in early or 

 mid-summer, the puparia were always formed at the base of 

 one of the larger outer leaves. A somewhat enlarged ex- 

 cavation is made, and here transformation occurs. The base 

 of the leaf around the puparium swells just a little, thus show- 

 ing a slight tendency towards gall formation. 



The larvae in the fall are always found mining on the 

 innermost leaves of the bundle. Just as the plant ceases 

 growth before winter sets in the larva enters and transforms 

 into a puparium. 



Fig. 81. Mine of Agromyza borealis on jewel-weed. 



In the spring when the plant resumes its growth, it is the 

 little leaf in the center which contains the puparium, that 

 causes the characteristic gall. Probably not over 20 to 25 

 per cent of the larvae enter the inner leaf and form galls. 



The jewelweed leaf -miner (Agromyza borealis Mall.) may 

 be found abundantly in moist or wet locations. These 

 flies have selected one of the thinnest of leaves to mine. 

 Although the leaves are thin and the plant very succulent, 

 wilting readily when plucked, the miners do not seem to 

 affect the leaves in any way except to make their characteris- 

 tic linear-blotch mines. 



The adults are marked with considerable yellow and when 

 resting in the sunshine glisten like gold. They have a 



