“ 57 
It will be noticed that the length of the various stages of the host 
has a direct relation to the number of enemies in each stage. The egg 
and pupa each exist as such only about one month and, in addition, are 
well protected in their earthen cells, hence we find but few natural ene- 
mies affecting them. On the other hand, the larva, which exists for a 
much longer period, is beset with enemies, among the most important of 
which are digger-wasps belonging to the genera Tiphia and Elis, which 
are thoroughly adapted to burrowing through the soil in search of their 
host. These parasites have undoubtedly been responsible for the practi- 
cal eradication of grubs in ceratin areas—sometimes rather restricted, 
which can be accounted for by the fact that Tiphia at least, on account 
of its large body and comparatively small wings, is unable to fly any 
great distance. Likewise, Tiphia, as well as all other white-grub para- 
sites, is somewhat checked in its increase by the length of its life cycle 
as compared with that of Phyllophaga, the parasite having a one-year, 
and the host, as a general rule, a three-year, cycle, and although grubs of 
a particular size are present each year there is seldom more than one 
destructive brood; that is, an abundance of a grub of a particular size 
occurs only every three years, and although the digger-wasp parasites 
may become very abundant one year they are likely to decrease in num- 
bers the following year on account of lack of host material. Another 
important detrimental influence affecting these wasps is plowing, which 
exposes the cocoon to heat and drouth in summer, to the cold of w inter, 
and to the attacks of predaceous mammals and birds. 
The adult dipterous flies of the genera Microphthalma and Ptilo- 
dexia are not adapted to enter the soil in search of their prey as is Tiphia, 
and must therefore deposit their young in cracks and crevices of the 
earth, the larvae being obliged to search for the grubs of their host 
insect ; hence it appears that these species are more abundant in sandy 
and porous soils which offer the least resistance to a search for the grubs. 
Whether the flies are able to locate infested areas and thus deposit their 
progeny in favorable locations is not known, but it seems likely that 
this is the case. The hymenopterous enemies of the genera Pelecinus 
and Ophion, and the Diptera belonging to the bombyliid genus Sparno- 
polius are so rarely encountered that they are of no appreciable 
importance in their influence on the grub, population. The beetles of the 
family Carabidae and their larvae are naturally predaceous and live in or 
on the surface of the soil, being always alert in their search for soft- 
bodied prey. Soil-inhabiting asilid and tabanid larvae are likewise gen- 
erally predaceous, but the Asilidae are much the more important as 
white-grub enemies because they inhabit upland soils which are favor- 
able to the development of most Phyllophaga species, while the Taban- 
idae are typically low-ground and marsh-inhabiting insects. Likewise 
we have in the Asilidae a most interesting example of a life cycle con- 
forming to that of Phyllophaga; at least it appears that two species of 
Promachus have a three-year cycle as does the host, and, furthermore, 
they are able to live for long periods without food—an adaptation of 
