202 
Bucentes (Siphona) geniculata 
Larvae collected in Lower Deeside and Lower Donside ( continued). 
Data for 1919. 
Lot 
Date 
Infected 
larvae 
Healthy 
larvae 
Total 
Percentage 
infected 
Craibstone. 
6. 
June 21 
13 
66 
79 
16-45 
7. 
„ 25 
23 
30 
60 
38-6 
8. 
„ 30 
(+ 7 otherwise 
infected) 
22 
49 
77 
28-5 
9. 
July 7 
( + 6 otherwise 
infected) 
6 
9 
15 
40-0 
Augustan, Cutter. 
10. 
April 26 
1158 
3467 
4625 
25-0 
11. 
May 2 
107 
456 
563 
19-0 
12. 
„ 9 
50 
903 
953 
5-2 
13. 
„ 16 
3 
807 
810 
0-37 
» 
1562 
7245 
8807 
17-6 
As is indicated in the foregoing table 
no infected 
larvae 
were obtained 
between May 16th and June 21st. This was the case in other areas in the 
north of Scotland of which several were examined. 
The fall to 0-6 per cent, at the beginning of May, and the complete absence 
of infected larvae in the soil for nearly five weeks, we attribute to the fact 
that the Bucentes maggots had pupated, and thus the Tipula larvae then 
found were such as had escaped infection by the parasite. 
Larvae obtained at Craibstone on June 21st showed an appreciable per¬ 
centage infected by Bucentes larvae, and from that date until July 7th, when 
the oats had grown too high to allow of further search for grubs, infected 
larvae continued to be obtained in high percentages, as is shown in the table. 
Number op Parasitic Larvae per Host. 
Observations made in 1918 show that one, two, three, and even four 
parasitic maggots may occur in one host. This was also the case in specimens 
found in the early months of 1919. A noticeable feature among the larvae 
found in the later part of 1919, viz. from June 21st onwards, was that there 
were seldom fewer than two Bucentes maggots in each host larva, 5—6 being 
common, and in one case as many as nine Bucentes maggots were found in a 
single host. 
Size of Parasitic Larvae pound. 
• . 
Larvae frQin 1-5 mm. up to 8-5 mm., which represents the maximum size, 
have been found. 
Even within the same host, the larvae may differ in size. For example, 
two maggots, 5 mm. in length, were found in the same host along wfith two 
others of 3 mm. In one case, where nine parasites occurred together, these 
were all 3 mm. in length. It seems more probable to us that these differences 
