206 
Bucentes (Siphona) geniculata 
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 dving 
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 1 . 
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 Cardbus, 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 Tkrixion Holidayanum, 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 bv 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 hooklets or spines 
which surround the stigmatic area of the parasite. 
Roubaud (1906) describes the relations between Siphona cristdta and its 
host, Tipula. gigantea, in the following terms: 
“A ce stade relativement jeune, chaque parasite est encore completement 
inclus dans un kyste ferine, membraneux, fixe au cordon tracheen par une 
sorte de calice chitineux dont le fond s ouvre dans la trachee chez les larves 
- . ■ 
1 The summary of the life history as given by Nielsen, is quoted on p. 203 
