THE CANADIAN ENTOMOLOGIST 373 



under such conditions and dependent upon weakly organized 

 adults for their establishment in favourable conditions. These 

 midges produce only a few eggs and evidently possess \'ery limited 

 powers of flight. The larva? are capable of penetrating only the 

 weaker, semi-rotten tissues of bark and sapwood and are preyed 

 upon by voracious maggots belonging to the genera Medeterus, 

 Lonchea and Lestodiplosis. All too frequently the only evidence 

 of Miastor infestation is the abundance of predaceous maggots 

 which have devoured practically every inhabitant of a once populous 

 colony. The ability to produce young in an indefinite series of 

 generations by maggots advancing in unoccupied tissue is a great 

 advantage in avoiding such enemies as those mentioned above. 

 We also have in this series of paedogenetic generations an example 

 of multiplication by geometrical progression such as obtains among 

 our plant-lice. 



Certain species like the Hessian-fly, sorghum midge, violet 

 midge and rose midge depend for existence to a considerable extent 

 upon the production of several generations annually ; in other words, 

 increase is by geometrical progression. The extraordinary efficiency 

 of this form of adaptation is strikingly illustrated in plant lice as 

 mentioned above. Such species, if able to subsist upon farm crops 

 or other products valuable to man, are potentially serious pests. 

 One generation annually appears to be the normal for many midges, 

 and consequently the ability to produce more in a season must be 

 considered a favourable adaptation to existing conditions. 



Midge galls. Recalling the fact that the more ancient type 

 of gall midges appears to be related to the fungus gnats or Myceto- 

 philidae and that they furthermore exhibit similar preferences in 

 that the larvae occur in organic matter in various stages of decay, 

 one would expect to find a series of galls showing gradual modifica- 

 t^'ons from this comparatively simple habitus to the more complex 

 type of shelter so frequently observed in this group. 



Bud galls. Possibly the simplest type of midge gall is to be 

 seen in the irregular, loosely and various developed bud galls pro- 

 duced by some species of Dasyneura and its allies. The eggs ap- 

 pear to be simply dropped among the developing floral organs or 

 leaves and the larvae obtain their sustenance by absorbing nutri- 

 ment from adjacent tissues. The weakening of the latter prevents 



