COMMON WHITE GRUBS. 15 
beneficial. The Tiphia larva, after devouring the grub, forms a 
characteristic cylindrical-ovate, ight brown, woolly cocoon about 
three-fourths inch in length (fig. 11, J), and from this the jet black 
digger wasp emerges the following spring. It in turn mates, and 
the female reenters the soil and there deposits its eggs on the grub, 
usually fastening them on the back of the latter just behind the head. 
The Elis cocoon (fig. 11, @) differs from the Tiphia cocoon (fig. 11, >) 
in that it is elliptical, slightly longer, and comparatively smooth. 
The adult emerging 
therefrom is about the 
same size as the Tiphia 
wasp, or slightly larger, 
and the black abdomen 
is transversely striped 
with yellow. The co- 
coons of both of these 
parasites are frequently 
turned out by the plow, 
especially in fields badly 
infested with white 
erubs. The parasitic fly 
Pyrgota undata Wied.’ 
(fig. 10) attacks only 
the beetle, usually de- 
positing its egg with- 
in the body of the beetle 
us the latter flies from 
leaf to leaf or to the 
ground at night. The 
Jarve hatching from 
these eges gradually 
kill the beetle, although Fic. 11.—Cocoons of wasps that prey on white grubs: 
as a rule the latter. if Peis ll : b, Tiphia inornata, Natural size. 
a female, is capable of | 
copulating and of depositing eggs for some days after being para- 
sitized; consequently this parasite may not be so valuable as might 
at first be anticipated. 
Several fungous and bacterial diseases have been reported attacking 
the grubs and beetles, but the knowledge of these is as yet superficial. 
Occasional outbreaks of these diseases have been reported, and it is 
highly probable that they serve as valuable natural checks. In 
Europe certain of these diseases have been artificially grown and used 
to destroy the grub, but there seems to be a divergence of opinion 
1JIt has been found that another species of Pyrgota (P. valida Warr.) is parasitic on 
the beetles, and this species may prove to be equally as important as P. undata, 
543 
