THE PARASITES OF POPILLIA JAPONIC A / 
per cent during the t ; me immediately following emergence, resulting 
in an abrupt reduction in numbers and the complete disappearance 
of the beetles by about the end of July, much earlier than would 
normally hare been the case. 
In 1921 this state of affairs was somewhat reversed, the beetles 
being approximately three times as abundant as in the previous 
year, whereas at no" time did more than 31 per cent of the females 
bear eggs. The 1922 season practically duplicated that of 1920 in 
beetle scarcity and parasite abundance, whereas in 1923 the condi- 
tions of 1921 were repeated. The numerical abundance of Centeter 
cinerea is therefore in an inverse ratio to that of the host, the parasite 
being abundant when the host is at its lowest point, and vice versa. 
In the years of beetle scarcity there is a great duplication of oviposi- 
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Fig. 6. — Curves showing the biennial broods of Popillia japonica at Sapporo. Japan, for 1920 to 
1923, inclusive, and the relative parasitism of the female beetles by Centeter cinerea: A, per- 
centage of beetles parasitized by C. cinerea; B, seasonal curve for abundance of adults 
of P. japonica, that for 1921 and 1923 being considered as approximately 100 per cent 
tion by the parasite, female beetles having been found bearing as 
many as 14 eggs upon the body, whereas the average for 1,135 para- 
sitized females was 4 eggs. Inasmuch as only one individual nor- 
mally develops in a single host, it is evident that at this point a con- 
siderable proportion of the potential rate of increase is lost. The 
final result is that the following year sees a reduction in the actual 
number of flies available to parasitize the much greater number of 
beetles. In consequence, very little oviposition duplication occurs, 
as is shown by the fact that cTf 401 beetles bearing eggs, the average 
number of eggs borne was 1.1 per parasitized female. As a direct 
result of this a much greater proportion attain maturity than in the 
preceding generation, and thus the biennial cycle once more begins. 
It may be well to consider the data obtained bv counts made in the 
field during the years 1921 to 1923, inclusive, at Sapporo and Koiwai. 
