SYRPHIDAE OF MAINE. 173 



Mr. R. C. Shannon 1 has recognized and recently described 

 this species as distinct from xanthostomus, under the name of 

 S \rphus knabi. The Ohio specimens from Pemphigus galls agree 

 quite closely with Shannon's description. The "Pemphigus-Gall 

 Syrphus-Fly" therefore should be called Syrphns knabi and not 

 Syrphiis xanthostomus. Syrphus knabi has also been reared in 

 Maine from the pseudo-galls formed of ash leaves by Prociphi- 

 lus fraxinifolii Fitch. The galls of Pemphigus oestlundi Cocker- 

 ell (P. vagabundus of authors) have never been recorded from 

 Maine. 



The metamorphoses of Syrphus xanthostomus Williston are 

 also under observation at the present time ; and, if there were any 

 possible room for doubt as to the specific separation of these two 

 species from examination of the adult alone, the immature stages 

 and biology show them to be abundantly distinct. 



These larvae were first taken in Maine on July 7, 1915, exact- 

 ly the date on which, four years previously, they were found in 

 the Pemphigus galls in Ohio. Additional specimens were collect- 

 ed July 16 and 21 and again on July 18, 1917. The larvae, at least 

 when nearly full grown, are found in the rather tightly-curled 

 parts of the leaves surrounded by numbers of empty skins of the 

 aphids, an eloquent witness to their ravages during growth. In 

 such situations they are only slightly less protected than in the 

 Pemphigus galls. 



The Pemphigus-gall larvae were described as follows : 



"Larva. Length about 10 mm. (8 to 11.5), width 3.75 to 4 mm., height 

 2.5 to 3 mm. Fat, thick, grub-like, sluggish larvae, elongate oviform in 

 outline, strongly arched dorsally (Fig. 12, B). Wrinkles prominent, pro- 

 duced laterally into an irregular, dorso-lateral carina; the ventral folds of 

 the body in the principal segments serve as very imperfect prolegs. Gen- 

 eral color very pale, pinkish-yellow. Heart line not conspicuous. Skin 

 bare, the segmental bristles short and light in color, very inconspicuous." 

 About 0.07 mm. long, of the usual two segments, the basal one about 0.23 

 mm. in diameter by a little longer, the distal one less than half as broad 

 at the base and accuminate. 



"The jaws of the mouth-parts are unusually short, their width at base 

 equal to their length, the lower jaw the heavier. Mouth-hooklets apparent- 

 ly three pairs : two near the jaws of which the ventral pair is the heavier, 

 the third pair lateral in position, heaviest of all. There are a number of 

 sensory papillae around the mouth-parts and antennae. The antennae are 



Proceedings of the Biological Society of Washington Vol. XXIX, p. 

 200, Sept. 22, 1916. 



