1913 ENTOMOLOGICAL SOCIETY. 95 



been well described by David Sharp in the Transactions of the Royal Dublin 

 Society for 1882. (2) Diminished resistance by, — 



(a) Eounding of the contours giving a boat-shaped form. 



(b) Depression of the eyes. 



(c) Loss of hair and sculpture. 



(d) Flattening of hind. legs in horizontal plane. 



(3) Increased efficiency of swimming of the hind legs. (4) Lowering the 

 centre of specific gravity by the formation of an air cavity under the Elytra. 



I cannot leave this discussion, however short, of the adaptation of aquatic 

 insects without again calling attention to this inviting field of research. Very 

 little has as yet been done, none of the groups have been monographed and but 

 few life-histories have been studied in detail. 



Turning our attention now to the economic significance of this insect life of 

 the water. These aquatic forms may be grouped into two general classes, herb- 

 ivors and carnivors. Now the primary crop of our waters, ponds, lakes, streams, 

 is fish. In order to utilise our ponds, streams, and lakes to their fullest extent* it 

 is necessary that they produce a crop which will be of value to man. How is this 

 to be bought about? Can we not utilise this insect fauna to our own advantage? 

 In other words why should we not have a system of water culture. Before we 

 can have any such system it is first necessary to know our water fauna and flora. I 

 mean know in the sense of life-histories, habits, food, times and rate of repro- 

 duction, means of propagating, isolating, etc., all those things that a progressive 

 farmer must kaow before he can successfully raise crops. It is becoming more 

 and more essential with our increasing cost of production and consequent high cost 

 of living that we utilise our open lakes, ponds and streams so that they may 

 produce a valuable crop as fishes. As Professor Needham has so often pointed 

 out, water is one of man'e primary pleasure grounds and sources of food supply. 

 At present it provides but a poor and uncertain crop which certainly could be 

 doubled and trebled if we only could develop as successful a water culture as we 

 have a land. culture. 



In order to have a successful water culture we must kave *(1) Isolation and 

 growth in pure culture, in other words we must eliminate or lighten the struggle 

 for existence. 



(2) Provide suitable environment. 



(3) Control the food supply and enemies. 



(4) Provide suitable varieties. 



So far as insects are concerned in a successful water culture they are im- 

 portant as a food supply, and in many cases dangerous as predaceous on small 

 fry as well as on insect herbivors. Prof. S.- iA. Forbes has shown in his studies 

 on fish food that insects constitute an important supply. He found Mayflies, 

 Midges, (adults and larvae), Caddis-worms, Water-boatmen, etc., in their 

 st«maohs. When we consider the enormous egg prodiiction of such mayflies as 

 Gallibaetis we see at onee an important source of food supply particularly when we 

 are able to control the rearing of these forms. Then there are periodic forms as 

 Blasturus, Siphlurus, Ephemera, Choroterpes, giving us an enormous food supply. 

 So also amongst Dragonflies. Then what an enormous food supply when we are 

 able to control the rearing of the many forms of aquatic Diptera, Trichoptera, etc. 

 Though many of the more general features of the life-histories have been worked 

 out, very little has bee» done in the way of successful rearing of these forms as the 



