DIPTERA. 



36; 



tlic pith, and thus causing the woody cells which surround it to 

 swell out, as in fig. 331. The galls are always found on the twigs 

 of the tree or bush, and between the 

 internodes. 



The perfect insects hatch out about 

 the middle of May (May 10, 1905, in 

 Northumberland), and deposit their eggs 

 in the twigs of last year's' shoots. The 

 larvae soon hatch out, and by their united 

 action, which creates a form of symbiosis, 

 stimulate excessive growth at the affected 

 part. The larvae feed right on through- 

 out the winter, and pupate within the 

 gall about April. The exit of the flies 

 may be recognised either by the flight- 

 holes or by the empty pupal-cases pro- 

 jecting from the gall. 



The fly is about 6 mm. in expanse of 

 wings. Eyes black, Antenme dark. 

 Wings hyaline, and at the base they are 

 of a light vermilion colour.' Halteres 

 white on the knob portion, and same 

 Thorax darkish, with two yellow -grey 

 variable in colour, sometimes dark 

 above and red below, but as a rule 

 darkish-grey above, and light with a 

 covering of silvery -grey hairs below. 

 Fig. 332 is a representation of the male. 



The larvae and pupae are of a light-yel- 

 low or orange colour, and, as a rule, from 

 1 2 to 30 are found in a sim>le chamber. 



Fig. 3&1.— Twig of Salix caprea 

 jurcd hy Cecidomyia salicis. 



colour as wings at base, 

 longish strips. Abdomen 



Cecidomyia (Dasyneuka) tiliam vol- 

 EKS, Eubs. ( = C. SALicis, Schrk.) 



This species forms galls on the ter- 

 minal shoots of lime-tree branches and 



the base of the leaf-stalk, about the size of a pea. The leaves are 

 deformed and disfigured, and growing with the point of the shoot 



Fig. 332.— Cecidomyia salicis ( 



