370 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
hoppers gradually increases during the summer months and reaches its height during 
August (35.1 per cent). The weak point in the parasitism of the leafhoppers occurs 
on the plains and foothills where 4.4 to 8.2 per cent were parasitized during the 
winter and 1 to 1.5 per cent during the spring. 
I. Introduction 
The importation of natural enemies to control introduced injurious 
insects in the United States and Insular possessions has been attempted 
with many pests. Although these imported parasites and predaceous 
insects assist in checking the multiplication and in certain years control 
the host, nevertheless, fluctuations in the abundance of the natural 
enemies and pest occur, so that parasitism can not be regarded as a de¬ 
pendable control year after year, except possibly in a few instances. 
II. Sugar Cane Leafhopper Controlled by Natural Enemies 
The best example generally known among sugar producers is the 
control of the cane leafhopper (.Perkinsiella saccharicida Kirk.) by natural 
enemies in the Hawaiian Islands. After the accidental introduction of 
the sugar cane leafhopper, many natural enemies already present in 
Hawaii transferred their attacks to this pest, but it was not until after 
special importations of parasitic and predaceous insects that the hopper 
was brought under complete subjection. In the cane fields today, a 
large number of different enemies prey upon the nymphs and adults, 
such as spiders, earwigs, long-horned grasshoppers, preying Mantids, 
kissing-bugs, ladybird beetles, Pipunculus flies, Dryinids, predatory 
wasps and others. According to Muir (8), natural enemies control 90 
per cent of the hoppers in the sugar cane fields. 
Egg Parasites. —Among the imported natural enemies, egg para¬ 
sites play an important role in the control of the cane leafhopper. 
It must not be assumed, however, that these egg parasites are the only 
factors in the control of the cane leafhopper. “When the hoppers in¬ 
crease to a serious extent through conditions unfavorable to the egg 
parasites, it is to the enemies of the nymphs and adults that we must 
look for a speedy reduction.” Muir (8). 
Local Outbreaks. —According to Muir (8), “every year there are a 
certain number of ‘outbreaks’ over limited areas. Most of these pass off 
without any appreciable damage to the cane, fully controlled by the 
parasites; a smaller number cause some damage before the parasites can 
control them, and a few do considerable damage.” 
