59 
predaceous larvae likewise may attack one another, we begin to realize 
the immense complexity of the interrelations of these animals. 
These few remarks indicate the importance of studying more thor- 
oughly the interrelations of insect pests and their enemies, and especially 
the effects of varying conditions on each—problems which are practically 
untouched, and yet ofter possibilities of the greatest economic impor- 
tance. 
Parasites of the larva 
Tue Buack Diccer-wasps (‘rputa spp.*) 
The black digger-wasps are without doubt the most efficient and 
abundant of the many parasites known to attack Phyllophaga. One or 
another of the species of Tiphia parasitic on our common white-grubs 
(Phyllophaga spp.) is to be found in greater or less abundance in every 
section of the United State east of the Rocky Mountains. 
The adult wasps feed on the nectar of various roadside flowers, 
but much of their life is spent in the soil and therefore they are not 
frequently encountered. However, the rather common occurrence of 
their tan-colored, woolly, egg-shaped cocoons in the soil, to be seen in 
following the plow in almost any section of the country, is sufficient 
proof of the beneficial activity of these wasps. 
The black digger-wasps were first recognized as parasitic, or more 
strictly speaking ectoparasitic, on white-grubs of the genus Phyllophaga 
by Riley, who in 1874 published an account of the habits and life history 
of a species which he referred to Say’s Tiphia inornata (59).~ Few 
additional facts were learned until 1907, when Forbes published an 
account (26) materially increasing our knowledge. Up to the present 
time, however, several species attacking white-grubs have been confused 
and practically nothing has been known of the different kinds. From 
our breeding records four species are now known to attack Phyllophaga 
larvae in the United States, each depositing its eggs on a different part 
of the grub, and several other species are parasitic on related grubs, such 
as Anomala, Ligyrus, Cyclocephala, Dyscinetus, etc. A fifth species 
(T. parallela Smith) is a parasite of the grub Phytalis smithii—a grub 
very mttch like our Phyllophaga—in the British West Indies, and, ac- 
cording to Nowell (53), the egg of this wasp is laid in a position 
identical with that of the egg of T. punctata on the Phyllophaga grub. 
T. punctata Rob., our commonest species, lays its egg on the dorsum 
of the thorax of the grub—or on the first or second abdominal segment— 
usually on the second or third thoracic segment, just to one side of the 
median line, in a groove of the folds of the skin; T. inornata Say com- 
-monly lays its egg on the under side of the thorax, usually between the 
legs, but occasionally beneath the first abdominal segment; T. transversa 
Say lays its egg on the under side of the abdomen, usually on the fourth 
* Determined by Mr. A. B. Gahan, and afterward checked up by Gahan using 
a key prepared by Mr. J. R. Malloch 
yj Numbers In parentheses refer to literature citations. 
