ORDER DIPTERA 247 



The larva. The larvae are soft, white, headless, legless, 

 maggots, as in other families of the higher Diptera, with two 

 pairs of spiracles one pair anterior and one posterior; and 

 with only a pair of cell-tearing mouth-hooks for feeding tools. 



The larvae of Agromyzidae have three types of anterior 

 spiracles — fan-shaped, semicircular, and forked. The first 

 two types are the commonest. In Phytomyza the anterior 

 spiracles tend to be approximated at the base, and project 

 rather prominently. Certain of the species have very 

 characteristic spiracles. In Phytomyza nigritella, for exam- 

 ple, the anterior spiracle is forked and has about twenty-six 

 stigmatal openings. 



The posterior spiracles in this family are even more varied 

 in form than the anterior spiracles. The number of stig- 

 matal openings resemble those of Pegomyia. The stigmatal 

 openings, where few in number, are arranged either subpar- 

 allel or radiating from a central point. The spiracles with a 

 larger number of stigmatal openings have various forms, 

 which are usually very characteristic of the species in which 

 they are found. 



It is not always easy to distinquish between the mouth 

 hooks of different species. The number of teeth varies 

 from two to four. In most species these sclerites are quad- 

 rangular in shape. Often they are unequal in size, the left 

 one being the smaller. In one species, Agromyza laterella, 

 they are triangular and have sharp teeth, somewhat resembl- 

 ing those in pegomyia. 



The ambulatory setulae are minute chitinized hooks which 

 encircle the edges of the segments in transverse bands. They 

 serve as a means of distinguishing Agromyza from Phy- 

 tomyza. In Agromyza they are almost always prominent, 

 while in Phytomyza they are either absent or exceedingly 

 minute. 



None of the Agromyzidae have prominent tubercles such 

 as are found in Authomyiidae. Some species of Agromyza 



