JOURNAL OF ECONOMIC ENTOMOLOGY 
376 
[Vol. 17 
there are but few native species of the United States which extend through 
the tropics into the south temperate zone. 
If it is demonstrated that the leafhopper through migratory flights, 
has established itself in localities outside the range of its efficient para¬ 
sites, then every effort should be made to introduce parasites into such 
natural breeding areas. Before any attempt is made to introduce 
natural enemies, a careful study should be undertaken of the habits of 
the parasites in their natural environment. If imported natural enemies 
were liberated on the plains and foothills of a natural breeding ground in 
California, and a spring dispersal of the parasites did not occur, they 
certainly would not survive after the pasture vegetation becomes dry. 
The habits of the parasites would require careful study in their native 
habitat to determine whether they would winter over in the cultivated 
regions or whether autumn dispersal and hibernation occur on the plains 
and foothills. Parasites should not be introduced into the migratory 
breeding districts of the leafhopper for it is a well known fact that when 
insects migrate from their natural breeding areas, they fail to establish 
themselves in their new environment unless they meet conditions identical 
with their original habitat. Preliminary experiments should be con¬ 
ducted with the egg parasites already attacking the eggs of the beet 
leafhopper in California to determine the proper methods of breeding 
them. There are many other factors to be taken into consideration in 
the importation of natural enemies, such as the question of general or 
specific primary parasites, secondary parasites, and environmental 
factors, which need no further discussion. 
V. Acknowledgments 
I am deeply indebted to Mr. A. H. Gahan, Bureau of Entomology, 
Washington, D. C., for the determination of the egg parasites bred in the 
San Joaquin Valley. Credit is due to Mr. W. J. Hartung for the de¬ 
termination of the percentage of parasitism of the spring and summer 
brood adults of 1919. 
VI. Bibliography 
1. Ball, E. D., 1917. The Beet Leafhopper and Curly Leaf Disease that it 
Transmits. Utah Agr. Exp. Sta., Bui. 155, pp. 1-56. 
2. Boncquet, P. A., 1923. Discovery of Curly Leaf of Sugar Beets in the Argentine 
Republic. Phytopath., XIII, No. 10, pp. 458-460. 
3. Brewer, W. H., and Watson, S., 1880. Geological Survey of California. 
Botany, I, pp. 94-95. 
4. Hall, H. M., and Clements, F. E., 1923. The Phylogenetic Method in Tax- 
