366 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 • 
SELECTIVE PARASITISM BY TIPHIA SP. 1 
By H. A. Jaynes, Assistant Entomologist , and T. R. Gardner, Junior Entomol¬ 
ogist, United States Department of Agriculture 
Abstract 
It has been observed during the past several years that the larvae of Ochrosidia 
immaculata became very numerous on a golf course in the vicinity of Moorestown, 
N. J. Within the past two years, the abundance of the larvae has been reduced 
approximately 95 per cent, by a native species of fossorial wasp belonging to the 
genus Tiphia. In the same manner the parasite increased in numbers and as the 
abundance of the host was reduced the numbers of the parasite decreased nearly 95 
per cent. At the same time a related Scarabaeid, Popillia japonica, became very 
numerous in the same locality. Under conditions in the field only two Popillia 
larvae were found to be successfully parasitized by the native Tiphias. Experiments 
which were conducted indicated that the female Tiphia deposited her eggs, by pre¬ 
ference, on the Ochrosidia rather than on Popillia larvae. The life histories of 
Ochrosidia immaculata and Popillia japonica are similar in this region, but the former 
larvae are larger than the latter, when both are full grown. Nevertheless during 
the latter part of August, when the Tiphias are present, many Popillia larvae have 
reached the third instar in their development; while many Ochrosidia larvae are in 
the second instar and are smaller than the Popillia larvae which have reached the 
third stage. 
It is evident that, at present, this species of Tiphia is selective in its preference 
for its native host, but since it is possible for some individuals to develop successfully 
on the Popillia grubs, it is possible the Tiphias may develop a strain which will 
become parasitic on this introduced species. 
For the past three seasons while studying native species of insects 
likely to become parasitic upon the larvae of Popillia japonica , several 
interesting points were observed relative to the parasitism of native 
Scarabaeid larvae. Most of our field observations were confined to an 
area of three or four square miles in the vicinity of Moorestown, N. J. 
During the summer of 1921, there was an infestation of Ochrosidia 
(Cyclocephla) immaculata on the Moorestown Golf Course. There were 
not enough larvae present to cause noticeable injury to the sod. The 
number of Japanese beetle larvae present was small since this territory 
had been infested for less than two years. Although search was made for 
native parasites, particularly species of Tiphia , none was found at this 
time. 
Abundance of Tiphias at Moorestown, N. J., in 1922 
In the summer of 1922, on the same course, it was noticed that areas 
of sod were loose and could be easily pulled up. Later in the season the 
grass died and turned brown. This condition of the sod was caused by 
Contribution from the Japanese Beetle Laboratory, Riverton, N. J. 
