MAPLE LEAF-MINERS. 411 



52. The ocellate leaf gall of the red maple. 



Sciara ocellaris Osteu Sacken. 



Order Diptera ; family Mycetophilid^e. 



(Plate xxxviii.) 



On the leaves of the red maple {Acer rubrum) circular ocellate spots about three- 

 eighths inch in diameter, with disk yellow, and margin and central dot, during one 

 stage of their growth, cherry-red. 



The following account of this fly is taken entire from Professor Com- 

 stock's report as U. S. Entomologist for 1881 : 



The foliage of the red maple {Acer rubrum) is often seriously injured by certain very 

 small larvsB, which make large and conspicuous spots or galls upon it. This insect 

 is apparently widely distributed. I have observed it both at Washington and at 

 Ithaca, N. Y. In the last-named place it occurs so abundantly that I have repeatedly 

 seen trees every leaf of which was infested. 



This insect is so small that of itself it would not readily attract attention, but the 

 result of its work is so conspicuous that it may be seen from a long distance. This 

 appears in the form of a circular spot, three-tenths to three-eighths inch in diameter, 

 which at a certain period of its growth is light yellosv in color, with a cherry-red 

 margin and central dot. (See pi. xxxviii, fig. 1.) At other periods the spot is simply 

 light green or yellow. Frequently these spots occur so thickly as to intersect each 

 other and to completely cover the leaf, fifty or more being on a single leaf. At the 

 center of each spot may be seen, on the other side of the leaf, an elevated portion. 

 Corresponding to this, on the lower surface of the leaf, there is a pit, within which 

 the larva lives. Larvae that were partially grown were found to be held in place in 

 the pit in the leaf by what appeared to be a larval skin. This pellicle covers the 

 body entirely, and is with difficulty removed from it ; the edges of the pellicle adhere 

 quite tightly to the leaf. Where the larva is full grown it forces itself from under 

 this skin, which then falls back into the cavity, or is pushed to one side, where fre- 

 quently it may be seen adhering to the leaf. The larva at this time drops to the 

 ground, into which it enters to undergo its transformation. 



The larviB are translucent, viscid, nearly colorless. Those m the galls are broad 

 oval (see pi. xxxviii, fig. 3) ; but those which have left them are more elongated, taper- 

 ing almost equally towards each end. On the lateral margin of each abdominal seg- 

 ment there are one or more short spines, which are directed towards the caudal end 

 of the body ; and on the dorsal surface of each abdominal segment, near each lateral 

 margin, there is a small tubular spiracle. There is a distinct head (see pi. xxxviii, 

 fig. 3a), which bears short but conspicuous antenna?. The caudal end of the body 

 (see pi. xxxviii, fig. 36) bears a pair of fleshy appendages, each of which is furnished 

 with a pair of spines similar to those on the margin of the segment, and a large 

 number of triangular teeth. 



The larva spins something like a cocoon a short distance below the surface of the 

 ground. To this cocoon the particles of sand firmly adhere so that it can be distin- 

 guished from the soil only with difficulty. The pupa is yellowish white, with large 

 black eyes. When the pupa is about to transform to an adult it emerges for about 

 two-thirds of its length from the cocoon. The pupa skin remains firmly attached in 

 this position. (See pi. xxxviii, fig. 4.) 



From larviB collected at Washington May 15, the adult emerged from June 14 to 

 June 16. I have not yet sufficient data to determine the number of generations each 

 year; but I believe there are several. Larvae were observed at Ithaca during the 

 latter part of September; they went into the grouud September 26. 



