188 INJURIOUS INSECTS OF 1904. 



Both of these flies belong to the family of gall-making- gnats 

 known as Cecidomyiidce. In it are found some of the most destruc- 

 tive insects, the Hessian fly, for example, the Wheat Midge, Willow 

 Gall Flies, etc. 



It is doubtful if any remedy is practical for the injury caused by 

 these insects, beyond the picking ofl: and destruction of affected 

 leaves containing the larvae, if the trees are small and few in num- 

 ber. Some repellant solution might possibly be sprayed on leaves 

 frequently during the season of the insect's attacks, and be more 

 or less eflfective. The gall-like growths caused by many flies in 

 this and other gall-making families — said growths being: seen in 



Fig. 173. — Four-winged Parasite, reared from maggots of Fly shown in Fig. 172. Original. 



willow, oak, golden rod, sumac, maple and countless other trees 

 and plants — are caused by the tissue of the plant in the immediate 

 vicinity of the tgg or larva making an abnormal growth, due evi- 

 dently either to the presence of an irritating agent placed there by 

 the parent insect, or by a secretion from the newly hatched larva, 

 or in some other way not at this time thoroughly understood. Two 

 hundred years and more ago it was believed that these growths on 

 plant, bush or tree were vegetable productions, and that the 

 "worms" found therein had arisen spontaneously. 



We have also reared this year Cccidomyia robiiiicr, Hald., from 

 galls on leaves of Locust, Rohinia. From this latter gall fly we 

 raised a four-winged parasite belonging to the group Peromalincr. 

 A Washington expert in this sub-family informs us that it repre- 

 sents apparently an undescribed genus. 



