106 Larval and Papal Stages of Bibio Joliannis L. 



The prothoracic spiracles project slightly in a dorso-lateral position. 

 The boundary between the prothorax and the mesothorax is not marked 

 on the dorsal side, while ventrally the leg- and wing-cases cover almost 

 the whole of the thorax. The abdomen is long, straight and slightly 

 flattened dorso-ventrally and consists of nine segments, the first six of 

 which are about equal. After the sixth segment the abdomen tapers 

 slightly, the last segment having the form of a blunt cone. The last 

 segment bears a pair of stout processes slightly dorsally near its tip, 

 which are nearly as long as the segment. 



Apart from these processes and the spiracles, the cuticle of the pupa 

 is bare. 



The abdomen bears a pair of spiracles on each segment except the 

 eighth. These spiracles project from slightly before the middle of the 

 sides of the segments. 



7. NOTE ON THE IMAGO. 



The adults emerged from the pupa on April 9th and the following 

 days, but their emergence was probably hastened by the warmer con- 

 ditions under which they were kept. 



The number of individuals of the different sexes, including the pupae 

 which were preserved as well as the adults which emerged, were, males 

 20, females 7, showing a considerable preponderance of males. 



8. ECONOMIC SIGNIFICANCE OF THE BIBIONIDAE. 



There appears to have been a considerable amount of uncertainty as 

 to whether larvae of this family are destructive to the roots of cultivated 

 plants. A number of instances are recorded of such damage by certain 

 species of this family, although Scharov(22) considers them harmless. 



Various species are recorded by Theobald (26) as attacking the roots 

 of oats, grass, lettuces, seedling cabbages and young flower plants, while 

 hops appear to be particularly badly attacked, especially by Dilophus 

 febrilis and D. vulgaris (20, 27). 



Carpenter (4) reports finding larvae of Bibio Marci feeding on potatoes, 

 while Collinge(5) states that Bibio Marci damages tomatoes, young 

 conifers, seedling ash and young spruce. He further adds that Bibio 

 Johannis damages larch seedlings and hop roots, and he considers that 

 these larvae are introduced in manure or leaf-mould. The larvae of 

 Bibio Marci are also recorded by Gillanders(iO) as injuring ash seed- 

 lings. 



