ORDER DIPTERA 263 



Perhaps the best known species in this family is the chrys- 

 anthemum miner, P. chrysanthemi, which has been most care- 

 fully studied by Smulyan (1914). It is a serious greenhouse 

 pest. It damages chrysanthemums, marquerites, few ferns, 

 and related compositae, by puncturing and mining the leaves. 



The adult is a small grayish fly, hardly a sixth of an inch 

 (4 mm.) in expanse of wings, being a yellowish color along 

 each side of the abdomen. It may be found resting on the 

 leaves of its host plant, or "crawling lazily about or making 

 its way from plant to plant in a skipping or hopping flight. 

 The eggs are laid simply in horizontal incisions made by the 

 ovipositor between the parenchyma or flesh and epidermis 

 or skin of the leaf." 



The egg punctures are in the lower surface; but the larva 

 or hatching soon passes to the upper or palisade layer of the 

 mesophyl and mines just beneath the upper epidermis, ex- 

 cavating an irregularly linear, often zigzagged and inter- 

 crossing tract, that is whittish in color and stands out promi- 

 nently on the green leaf. 



The mine is gradually widened and at the last it is 

 deepened also to form a cavity in which pupation takes 

 place. The boat shaped puparium is visible through the 

 transparent epidermis. Ordinarily only the minute ante- 

 rior spiracles are protruded through the epidermis. 



Smulyan's (1914) seasonal notes on the mean life cycle are 

 as follows: 



dayt 



Time elapsing between emergence of adult and ovi position .... 1^ 



Length of egg stage 5 



Length of larval stages 13 



Length of papal stage 14 



Average length of one generation 33^ 



The wild lettuce leaf miner {Phytomyza lactuca Frost) 

 is common and has been found wherever the lettuce occurs 



