THE PARASITES OF POPILLIA JAPONICA 
15 
and the sky somewhat overcast. Under these conditions the beetles 
remain upon the foliage throughout the day, in contrast with their 
disappearance about noon on days when the temperature is high and 
the sunlight intense. This gives the fly a greater opportunity to 
oviposit, and its own inclination to continue this throughout the day 
rather than to remain quiescent on the foliage results in a much 
increased deposition of eggs. 
The manner of oviposition is very unusual in that it leads to the 
placement of the egg on a restricted portion of the host body. In 
case the beetles attacked are feeding singly upon the foliage they 
take alarm immediately 
a fly alights in the vicin- 
ity, and a closer ap- 
proach leads them to 
drop to the ground. For 
this reason oviposition 
normally takes place 
upon mating pairs, since 
these do not take alarm 
so readily. The female 
fly may stand about on 
the leaf for some time, 
apparently watching the 
beetles, after which she 
makes a dash for the 
pair, running diagonally 
across the thorax of the 
female and pausing only 
for an instant to place 
an egg thereon. About 
98 per cent of all eggs 
laid are so placed and, 
under normal conditions 
such as prevail at Koiwai, 
about 85 to 96 per cent 
are upon female beetles. 
This has a very impor- 
tant bearing upon the 
effectiveness of the par- 
asite. 
Oviposition occurs at 
times on other parts of 
the beetle body. Occasionally a fly will approach the host from the rear, 
in which case the egg is placed upon the elytra, or from the side, when it 
may be laid on one of the legs. The greater proportion of misplaced 
eggs, however, are ventrally on the thorax, these having been so placed 
by oviposition through a hole in the leaf. Instances have been observed 
of female flies alighting directly upon the beetles from flight, and here 
there is no uniformity in the position of the egg. Occasionally a 
pronounced struggle may take place between the fly and the beetle, 
and both may drop) to the ground. In this event, however, the 
attempt to oviposit is seldom successful. 
The rate and duration of oviposition under laboratory conditions 
were observed in a series of 24 females collected in the field sufficiently 
Fig. 13. — Reproductive organs of female Centeter cinerea 
