THE SUGAR-CANE LEAFHOPPER. il 
SUGAR-CANE INSECTS. 
The advent of a serious pest into the Hawaiian sugar-cane fields, 
the sugar-cane leafhopper (Perkinsiella saccharicida WKirk.), between 
1900 and 1902 and the widespread injury of this insect throughout 
the sugar-cane districts in 1903 led to the establishment of an ento- 
mological division in the Sugar Planters’ Experiment Station in 
September, 1904. In this division detailed studies have been made 
of the species of insects occurring in the Hawaiian cane fields, the 
investigations relating particularly to the leafhopper and its natural 
enemies. 
Koebele® has earlier discussed the sugar-cane insects. Up to the 
time of the leafhopper invasion the sugar-cane borer ([Sphenophorus] 
Rhabdoenemis obscurus Boisd.) was the most injurious species. The 
sugar-cane aphis (Aphis sacchari Zehntner), the sugar-cane mealy-bug 
(Pseudococcus calceolarix Maskell), the leaf-roller (Omiodes accepta 
Butler), cutworms, and certain other pests occurred locally, but up 
to this time no detailed study of their injury had been made. 
An insect enemy of sugar cane has exceptional advantages for 
development in the Hawaiian Islands. Approximately only one- 
half the total area is harvested at any one time. Thus the great 
extent of the plant gives an abundant supply of food, while the system 
of cropping provides a continuous supply. These conditions, 
together with the even climate, favor the uninterrupted breeding 
of any enemy of the plant. A further factor in the undue increase 
of the cane-feeding insects is the impetus to development arising 
from the absence of the special parasitic and predaceous enemies 
of the plant-feeding species. The absence of natural enemies is 
understood when it is known that the islands are isolated from all 
continental areas and that the economic plants are introduced forms 
for which the native flora has made way, carrying with it the endemic 
species of insects, while the insect enemies of a cultivated plant are 
of foreign origin, introduced into the islands with their host plant 
but without their natural enemies. These very facts, together with 
the almost total absence of secondary parasites as a grotip and the 
opportunity of eliminating them when introductions are made, 
furnish ideal conditions for the mtroduction and establishment of 
special parasitic imsects. The greatest factor in the successful 
establishment of a special parasite is the absence of the secondary 
parasites of which it is the host. One can understand why emphasis 
has been placed on the use of natural enemies in the control of 
injurious species in Hawaii and why also greater success has been 

@ Hawaiian Planters’ Monthly, vol. 15, no. 12, pp. 590-598, December, 1896; vol. 
17, nos. 5 and 6, pp. 208-219 and 258-269, May and June, 1898; vol. 18, no. 12, pp. 
576-578, December, 1899; vol. 19, no. 11, pp. 519-524, November, 1900. 
