[ 1«5 ] 



in size in parasites occurring together are due to variations in the rate of 

 growth than that the same host should have been parasitised on two or more 

 separate occasions. 



DuBATiON OF Larval Period. 



First Generation. In the season 1918, Bucentes larvae were obtained as 

 early as February 20th. These larvae were on an average about 4 or 5 mm. in 

 length at this date. In 1919, these larvae were first obtained on February 

 28th; they were from 3 to 5 mm. in length. This suggests that the parasitic 

 larvae found in February are the product of eggs laid the previous autumn, 

 the larvae having hibernated in the host. 



Second Generation. From June 21st onwards, large percentages of the 

 collected host larvae were found to be infected with Bucentes, whose maggots 

 were of such a size, viz. 1-3 mm., as to lead to the suspicion that the Tijmla 

 larvae had been recently infected. From these Bucentes maggots a second 

 generation of flies was bred which began to emerge .on July 25th. An earlier 

 generation of flies was bred out in May and the early part of June and by 

 June 13th all these flies had died. Moreover, from May 16th to June 16th 

 Tipula larvae were collected on four different occasions, to the number of 

 355, and of these none were found to be infected by Bucentes. This evidently 

 indicates that all the parasites had pupated, involving the death of the 

 host larvae, so that the Tipula larvae collected between these dates were those 

 which had escaped infection by Bucentes during the previous autumn. In 

 view of the foregoing, viz. that there is a period of over four weeks during 

 which no infected Tipula larvae can be found in the field, that within this 

 period adult flies appear to die off and that subsequently infected larvae 

 again appear, the conclusion seems obvious that a second generation of 

 B. geniculata commences about this time. 



Bucentes maggots of the second generation were observed on June 16th, 

 when they measured about 3 mm. The earliest date on which mating was 

 observed was June 2nd, and no imagines survived in the observation cage 

 after June 13th. Oviposition, and the infection of Tipula larvae in the field, 

 may therefore be assumed to take place approximately within a corresponding 

 number of days. Pupation of the second generation of larvae was observed 

 to begin in the experimental cage about July 8th. That is to say, the maximum 

 extent of the larval period possible was in this case from June 3rd to July 

 8th, viz. five weeks. This estimate is only an approximate one, as oviposition 

 has not been observed and the period which elapses between oviposition and 

 the hatching of the larva is unknown. 



We have been able to find in the literature dealing with this subject only 

 the scantiest references to this species. Nielsen (1918), in a table showing the 

 life cycle of a number of Tachinidae, includes Bucentes geniculata in the form 

 reproduced below, wherein P. signifies Pupa, L. = Larva, I. = Imago. 



April — May June July Aug. Sept. Oct. Nov. — April 

 Bucentes geniculata P.I L.P.I. I. I.L. I.L. P. P. 



