December, ’24] 
severin: beet leafhopper fluctuations 
639 
out of sight under the orange peel. As a further test I placed some 
larvae in small individual cages on oranges hanging on the trees and 
found that most of the larvae fed on the fruits. 
These moths occur in Orange and Los Angeles Counties together 
with Tortrix citrana Fer. There are some Holcocera present in prac¬ 
tically all orange groves but the trees that are dirty because of scale in¬ 
sects are apparently more heavily infested. In Orange County, at 
present, there are more Holcocera than Tortrix. 
This is not a new insect as we learn by its history but it seems to have 
digressed from its original habits of scavenger and predator on scale in¬ 
sects to a secondary feeder on oranges where it occurs in the citrus dis¬ 
tricts. Tortrix citrana and Platynota tinctana Walker have received the 
blame for the wormy oranges in Southern California but I am sure that 
Holcocera iceryaeella has been responsible for some of the damaged fruits, 
perhaps for most of the wormy oranges that formerly were supposed to 
have been caused by Platynota tinctana Walker, which I have found too 
sparingly in the citrus areas of Los Angeles and Orange Counties during 
the past year to even cause a noticeable amount of wormy fruit. 
References 
1. Riley, C. V. Report Comm. Agri. 1886, 485, 1887. 
2. Essig, E. O. Jour. Ec. Ent., 9, 369, 1916. 
3 Horton, J. R. U. S. D. A. Bui. 647, 30, 1918. 
CAUSES OF FLUCTUATION IN NUMBERS OF BEET LEAF- 
HOPPERS (.EUTETTIX TENELLA BAKER) IN A NATURAL 
BREEDING AREA OF THE SAN JOAQUIN 
VALLEY IN CALIFORNIA 
By Henry H. P. Severin, Ph.D., California Agricultural Experiment Station 
Abstract 
The primary cause for the enormous increase of the beet leafhoppers during 1919, 
hinges on two factors: (1) there were no summer migrations of the pest during 1918, 
so that a large number of eggs were deposited during the autumn; (2) the nymphs 
which hatched from these eggs found an abundance of green food not only in the 
cultivated areas but also on the plains and foothills after the heavy September rains 
germinated the seeds of the vegetation. 
The factors associated with the reduction in numbers of the beet leafhoppers vary 
in different years. The primary cause for the enormous reduction in numbers of the 
spring brood hoppers on the plains and foothills during 1923, was due to the early 
drying of the pasture vegetation during March instead of April and May as in previous 
years from 1919 to 1922. Secondary factors which reduce the number of leafhoppers 
in a natural breeding ground are natural enemies, spring and summer migrations, 
fungus diseases and rainfall. 
