ET-184 October 1941
United States Department of Agriculture
Bureau of Entomology and Plant Quarantine
METHOD FOR SECURING DIRECT FIELD INOCULATIONS IN STUDIES OF
By Howard E. Dorst,
Division of Truck Crop and Garden Insect Investigations
The technique !_/ here described makes possible a direct
transfer of insects from the host to the test plant in studies to
determine the percentage of viruliferous carriers. The method may
be used in other studies, but it is adapted particularly for the
use of small test plants where the source of insect population is
distant from the laboratory.
Wallace and Murphy,/ in their studies of curly-top disease,
made indirect transfers from wild host plants to beets because the
flowerpots in which the beets were grown could not be conveniently
transported to the field.
A direct transfer of insects from a wild host to beets or
to a test plant in virus-disease studies is advantageous because
it eliminates 'the possibility of modification or reduction of the
virus content of the insects by their feeding on susceptible hos.s
used in transporting the leafhoppers to the laboratory. A hibh
mortality often occurs when it is necessary to transfer the leaf-
hoppers from one food plant to another.
The method described involves the use of trays of convenient
size for transporting the test plants to the field so that the leaf-
hoppers may be transferred directly from the host plant. The trays
are about 5 inches deep and are divided into individual blocks
about 2 inches square by stretching strings across the tray to mark
off squares. The string conveniently separates the plants in an
orderly arrangement so that individual inoculation records may to
economically maintained. A single beet seed is planted in each
I/ This technique was developed in cooperation with the Utah
Agricultural Experiment Station.
2/ Wallace, J. M., and Murphy, A. M. Studies of the Epidem-
iology of Curly Top in Southern Idaho, with Special Reference to
Sugar Beets and Weed Hcsts of the Vector EvtettJx tenellus. U. S.
Dept. Agr. Tech, Bul. 624. 1938.
square. Occasionally it may be necessary to transplant a few plants
to the squares where germination was not secured. A single beet
leafhopper is placed in each clip cage, which is attached to the
leaf of an individual beet plant. The leafhoppers are usually col-
lected from the host plant by means of an insect net and transferred
to a celluloid cylinder, from which individual specimens may be
segregated, by the use of a small pipette, for placement in the
clip cages. The trays can be returned to the greenhouse or any other
optimum environment for the development of the disease. By simply
screening the openings of the greenhouse, the chance of infection
by extraneous virulifercus beet leafhoppers is minimized.
Figure l.-Clip cages used to isolate individual leafhoppers
on separate beet plants.
Figure 2.-Vertical view of a tray of small beets with the
clip cages attached. String separates the tray into
squares, and each square contains one beet plant.
UNIVERSITY OF FLORIDA
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