164 Forty-ninth Keport on the State Museum 



European History of the Insect. 



Baron Osten Sacken, in response to an inquiry, has kindly given me 



the following account of its occurrence in Europe : 



The gall you send also occurs in Europe on Betula alba ; it was first 

 discovered by Kaltenbach, who communicated it to Winnertz. The latter 

 published a rather imperfect description, drawn from dry specimens 

 {Cecid. ^^/«Ag male and femaki in Linnsea Entom., viii, p. 234; 1853). 

 In 1878 Dr. Franz Low in Vienna published an article on the same fly 

 with figures of the gall ; he corrected some of VVinnertz's statements, show- 

 ing for instance that the male antennae count 14, the female antennae 15 

 joints (Verb. Zool. Bot. Ges. in Vienna 1878, pp. 15-17, Taf. IV, fig. 4). 

 In the same year, 1878, but independently from Low, Mr. Wachtl in 

 Vienna described and figured the same gall in his Entomol. Biolog. 

 Studien, Serie I, pp. 9-1 1. He found it not only on Betula alba, but also 

 on a Swedish variety of B. pendula, called B. valecardia Linn. He also 

 bred a parasite, Toiytnus pallidicornis Boh., and found the pupa of the 

 fly, Leucopis griseola among the galls. 



Description of the Insect. 



The following description of the larva has been prepared from specimens 

 taken from the galls September 11, 1896. 



Larva (full grown). — Length 0.06 in. ; width about 0.02 in.; form oval; 

 color a light orange; segments distinct — 14, as in other Cecidomyid larvae. 

 The skin is smooth and is sparsely invested with glandular, seta-hke pro- 

 cesses which are longer anteriorly — they appear more like direct con- 

 tinuations of the dermis than ordinary setae. The structure of the head 

 could not be determined satisfactorily from the material at hand. 



Later the larva becomes somewhat thicker and more rotund : color a 

 deep orange ; surface of the skin finely corrugated and without the seta- 

 hke processes described above. It was inclosed in a fine white cocoon 

 which is probably excreted as it appears to have no filamentous structure 

 even under a powerful microscope — possibly the cocoon is excreted by 

 the seta-like processes. 



'' The perfect insect is a dusky yellow, with the top of the thorax black ; 

 the abdomen also occasionally dark. Legs pale yellow. Antennae dark 

 brown, 12 to 13 jointed in male, apical joint with a very short petiole; 

 in the female 12 sessile joints. Wings limpid; transverse veinlet placed 

 a short distance before the middle of the first longitudinal vein [? sub- 

 costa] ; second longitudinal [radius] nearly straight, joining the costa near 

 the tip of the wing ; the second branch of the third longitudinal [cubitus] 

 bending round to the hind border. Halteres grayish-white. Third seg- 

 ment of oviduct white ; no valves." (Theobald.) 



