[ 168 ] 



The winter months are spent as larvae within their hosts, viz. Tipula 

 larvae. Pupation may start as early as the beginning of April if the season 

 is good but in a late season, pupation may not begin until nearly the end of 

 this month. After a pupal period of about three weeks the imagines emerge 

 during April and May. By the middle of June the adult Bucentes are dying 

 off. A second generation appears in June. After a larval period of about 

 three weeks and a pupal period of about seventeen days the adult flies emerge 

 towards the end of July. Since Tipula larvae are found in the winter months 

 parasitised with Bucentes, infection probably takes place in the autumn 

 whilst the Tipula larvae are comparatively young^. 



Structural relations of the Parasitic Larva to its Host. 



Dufour (1827) described the larva of the Tachinid Ocyptera bicolor, which 

 inhabits the body cavity of an Hemipteron, Pentatoma grisea Latr. He 

 observed a membranous funnel-like structure, equal to about one- third of 

 the length of the larva, extending from the last segment of the body and 

 adhering by means of a pair of horny teeth at the other end to a metathoracic 

 stigma of its host. He noted that this "siphon" could be detached from the 

 larva without injuring it and he also found in other cases, "siphons" adherent 

 to the metathoracic stigmata of the Pentatoma in the absence of the parasitic 

 larvae. 



Kunkel d'Herculais (1879) described a similar structure in the larva of 

 Gymnosoma rotundatum Linn., and regarded the siphon as a product of the 

 larva. In a Tachinid larva of Carabus, Cholodkowsky (1884) found a similar 

 structure fixed to a trachea and described it as a chitinous funnel. He inter- 

 preted this as a pathological chitinous product produced by the hypodermal 

 layer of the trachea at the point where the larva, having entered by a stigma, 

 perforated the tracheal system to reach the body cavity. 



Pantel (1898 and 1909), in Thrixion Halidayanum, clearly established the 

 true nature of this funnel as an inflammatory reaction on the part of the host, 

 and has more particularly shown how these anatomical relations are estab- 

 lished between the host and parasite by a development of the hypodermal 

 cells of the skin or of the trachea, whichever structure was utilised by the 

 larva as a means of bringing its stigmata into direct relation with the external 

 air. The perforation of the host's tissue at the point where attachment eventu- 

 ally takes place is effected primarily by means of the booklets or spines 

 which surround the stigmatic area of the parasite. 



Roubaud (1906) describes the relations between Siphona cristata and its 

 host, Tipula giganlea, in the following terms : 



"A ce stade relativement jeune, chaque parasite est encore completement 

 inclus dans un kyste ferme, membraneux, fixe au cordon tracheen par une 

 fiorte de calice chitineux dont le fond s'ouvre dans la trachee chez les larves 



' The summary of the life history as given by Nielsen, is quoted on p. 165 



