POLYSCELIS MODESTUS GAHAN, A MINOR PARASITE OF 
THE HESSIAN FLY 1 
By P. R. Myers 2 
Assistant Entomologist, Cereal and Forage Insect Investigations, Bureau of Ento¬ 
mology, United States Department of Agriculture 
INTRODUCTION AND HISTORY 
The hymenopterous parasite which 
is the subject of this paper w'as first 
reared from the Hessian fly ( Phytoph- 
aga destructor Say) in the summer of 
1915 by the late W. R. McConnell and 
the author at the Hagerstown, Md., 
Laboratory of the Cereal and Forage 
Insect Investigations of the Bureau of 
Entomology, United States Department 
of Agriculture, when a heavy infesta¬ 
tion of that insect pest of wheat occurred 
generally throughout the wheat-growing 
region of the Eastern States. 
At that time specimens of this species 
were submitted for determination to 
A. B. Gahan, of the Bureau of Ento¬ 
mology, who tentatively determined 
them as Polyscelis sp. A subsequent 
examination of the material and litera¬ 
ture, however, revealed it to be a new 
species and accordingly it was de¬ 
scribed by Mr. Gahan 3 in 1922 under 
the name Poly seeks modestus . 4 
Although knowledge of this species 
is rather meager, it seems advisable to 
record the data which have accumu¬ 
lated concerning its life history, espec¬ 
ially in view of the fact that the species 
is uncommon and no recoveries of it 
have been made since 1918. 
DISTRIBUTION 
The first specimens of this species 
were reared from Hessian fly puparia 
collected by the author in 1915 near 
Hanover, Pa. Later on, however, 
specimens were reared from material 
collected in the following five additional 
localities in the States of Maryland 
and Pennsylvania: Hagerstown, Md. 
(W. R. McConnell, E. M. Craighead); 
Andersonburg, Carlisle, Gettysburg, 
and Perkasie, Pa. (P. R. Myers). 
HOSTS 
Normally Poly seeks modestus is a 
primary, solitary parasite of the Hes¬ 
sian fly. The primary nature of its 
attack on this host has been demon¬ 
strated on several occasions by breed¬ 
ing it experimentally in the labora¬ 
tory upon nonparasitized Hessian fly 
puparia. It attacks the host usually 
in the larval stage but cases have been 
found where it has developed also upon 
Hessian fly pupae. It feeds externally 
on its host within the puparium. Com¬ 
pleting its development within the 
puparium, it emerges therefrom as an 
adult. 
This species has also been shown to 
be a secondary parasite by the rearing 
of a single minute male from a pupa¬ 
rium which, wdien opened, was found 
to contain the cocoons of a platy- 
gasterid parasite, probably Platygaster 
vernalis (Myers). 
In another instance two eggs of P. 
modestus were deposited within the 
same puparium. Shortly after the 
hatching of these eggs one of the result¬ 
ing larvae attacked the other and by 
the following day had consumed its 
contents. Evidence was also found 
indicating that young larvae probably 
attack and destroy the eggs of their 
own species. 
These cases of hyperparasitism and 
hyperpredacity plainly indicate that 
upon occasion this species can develop 
upon parasitic larvae, and probably 
pupae, of its own or some other species 
as well as on the larvae and pupae of 
the Hessian fly. 
ECONOMIC IMPORTANCE 
Although this species was easily 
reared upon nonparasitized Hessian 
1 Received for publication July 26, 1924. Issued January, 1925. 
2 The biological data contained in this article were obtained principally from experiments con¬ 
ducted by the late W. R. McConnell in the laboratory of Cereal and Forage Insect Investigations, 
Bureau of Entomology, United States Department of Agriculture, at Carlisle, Pa., during the summer 
of 1917. The writer gladly expresses his indebtedness to Miss Esther H. Hart for the drawings of the 
adult and the leg, wings, and antennae of adults; and to C. C. Hill for the drawings of the egg, larva, 
pupa, and parts of larva, and for kindly criticisms. 
3 Gahan, A. B., descriptions of miscellaneous new reared parasitic hymenoptera. Proc. 
U. S. Nat. Mus., 61: 11-12. 1922. 
4 Order Hymenoptera, superfamily Chalcidoidea, family Pteromalidae. 
Journal of Agricultural Research, 
Washington, D. C. 
( 289 ) 
Vol. XXIX, No.6 
Sept. 15, 1924 
Key No. K—146 
