1905.] Gall-Gnats on Osiers and Willows. 499 



The Gall-Gnat family, or Cecidomyilce, is a family of two- 

 winged or dipterous insects. These flies are tiny, delicate 

 in structure, and with few nervures to the 



Gall-Gnats wings ; their somewhat long antennae have, 

 Injurious to Osiers ^ . ' ' . • r ^ u . . , 

 and Willows. typically, whorls of fine hairs at the joints ; 



the legs are long and slender ; the hairs 



on wings and body are easily rubbed off. The larvae are small 



maggots, and some have at the front end, on the lower surface of 



the body, a so-called anchor-plate or "breast bone," which 



may be used for leaping or for changing position, or, perhaps, 



in feeding. 



The food habits of the larvae vary considerably, but all the 

 willow-infesting species are found in characteristic galls or 

 malformations, the galls being on young or older twigs, at the 

 apices of twigs, on flower buds, and on leaves. 



The pupal stage is generally in the gall, but in some cases in 

 the soil. 



Cecidomyia (Rhabdopkaga) saliciperda. 



This species infests Salix alba, S. fragilis, S. caprea, S. pur- 

 purea, S. viminalis, and exceptionally White Poplar. Young 

 twigs are attacked, and parts up to 3 or 4 in. in diameter. 



Symptoms of infestation are poor leafage, swellings, and later 

 the rupture of the bark, which hangs down in shreds. 



Description of Insects. — The fly measures only 2 to 3 mm. 

 in length ; its head and thorax are black or black-brown, with 

 black hairing ; the wings are milky white, with whitish hairs. 

 The extremely minute eggs, rounded at the ends, are orange 

 yellow in colour. The larvae are rounded at both ends or 

 somewhat spindle-shaped, and have a well-marked anchor- 

 process. The pupa is yellow, and has at the base of the 

 antennae two small brown projections. 



Life History. — The female lays her eggs in chains or rows 

 on the bark. The larvae on hatching bore into the bark, and 

 owing to their irritating presence the cambium gives rise to 

 irregular streak-like growths, through which the larvae make 

 excavations or irregular galleries. Between the larval galleries 

 the wood is normal in condition. Perhaps the activity of the 

 cambium may serve to enclose the larvae without marked boring 

 on their part. 



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