AGAMERMIS DECAUDATA COBB, STEINER, AND CHRIS¬ 
TIE; A NEMA PARASITE OF GRASSHOPPERS AND 
OTHER INSECTS . 1 
By N. A. Cobb, Agricultural Technologist in Charge; G. STEINER, Nematologist and 
Technologist , and J. R. Christie, Assistant Nematalogist, Office of Agricultural Tech - 
no logy, Bureau of Plant Industry , United States Department of Agriculture 
INTRODUCTION 
This is a preliminary account of a joint investigation carried on at 
Washington, D. C., and Falls Church, Va., and relates to a nema Agamer- 
mis decaudata, parasitic in insects, particularly in Orthoptera. The work at 
Falls Church is carried on with the cooperation of the Bureau of Ento¬ 
mology at its eastern field station, and all the insects examined have been 
determined by officers of that bureau. Other valuable assistance has 
been rendered by approximately 150 American zoologists and entomolo¬ 
gists, whose aid has made possible a first tentative map of distribution 
of the parasite in the United States. 
The general oversight of the work has been handled by the senior 
author, who has given special attention also to methods and apparatus, 
and to the structure and behavior of the free-living larva. Dr. Steiner 
gave special attention to the structure and taxonomy of the parasitic 
and post-parasitic stages. He has also handled nearly entirely the diffi¬ 
cult matter of the literature and nomenclature. Prof. Christie has given 
special attention to field and laboratory work connected with the hosts 
and their habits, the effect on the host, the habits and distribution of 
the post-parasitic forms in the soil under natural conditions, and to the 
rearing of both host and parasite. 
In the present account it is not proposed to do more than sketch some 
of the main features of the work, which has involved thousands of dissec¬ 
tions, hundreds of carefully executed laboratory and rearing experiments, 
and the invention and trial of dozens of different pieces of special appara¬ 
tus adapted to various features of the work. 
A broad numerical basis has been given the facts disclosed, since the 
work has for its definite object the economic application of the data 
secured. The summary presents two aspects, the latter of which is sub¬ 
divided : First, the results show positively that, in certain cases believed 
to be typical, the nema Agamermis decaudata , is an important factor in 
the birth rate of certain injurious insects; second, the application of this 
fact may be exploited in two ways, (a) by colonization—that is, moving 
the parasite from places where it exists to places where it does not exist, 
or is rare; the experiments show that this can be done, either by trans¬ 
ferring diseased insects, such as grasshoppers, or by transferring the para¬ 
site itself in one form or another; ( b ) by forecast—since methods of de¬ 
tecting the parasite have been developed to a point where it is believed 
possible to hazard some form of prediction. Just as, if we can not con¬ 
trol the weather, it is at least important to be able to predict it, so, if 
we can not prevent the ravages of an insect, it is at least important to 
be able to predict when the ravages are likely to occur. In this respect 
the results of the investigations are considered positive. 
1 Accepted for publication Mar. 7, 1923. 
Journal of Agricultural Research. 
Washington, D. C. 
adq 
27971 
(921) 
Vol. XXIII. No. 11 
Mar. 17,1923 
Key No. G-290 
